Contributions to economic geology, 1908. Part II, Mineral fuels

Marius Robinson Campbell, Geological Survey (U.S.) · 1910 · Historical

Contributions to economic geology, 1908. Part II, Mineral fuels by Marius Robinson Campbell, Geological Survey (U.S.) (1910). Full text and reference in the…

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The Branner Geological Library

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Dei'Artmrkt (If Thk Interior United States Okoixwical Survey

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Economic Geology

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Contents.

rage.

Introduction, by M. R. Campbell 5

Coal and lignite:

Stratigraphy and coal beds of the Indiana coal field, by G. H. Ashley. ... 9

The Washburn lignite field, North Dakota, by ( D. Smith 19

The Fort Berthold Indian Reservation lignite field, North Dakota, by ( D.

Smith 30

The Fort Peck Indian Reservation lignite field, Montana, by C. D. Smith. 40 The central part of the Bull Mountain coal field, Montana, by R. W. Richards 60

The Milk River coal field, Montana, by L. J. Pepperberg 82

Notes on the coals of the Custer National Forest, Montana, by ('. II. Wege-

mann 108

The Powder River coal field, Wyoming, adjacent to the Burlington Railroad, by R. W. Stone and C.T. Lupton 115

The Buffalo coal field, Wyoming, by H. S. Gale and II. Wegemann. . . 137 The coal field in the southeastern part of the Bighorn Bain, Wyoming, by

E. G. Woodruff 1 70

The eastern part of the Little Snake River coal field, Wyoming, by M. W.

Ball and Eugene Stebinger 186

The southern part of the Rock Springs coal field, Sweetwater County, Wyo.,

by A. R.schultz '. 214

Weathering of coal in the arid region of the Green River Basin, Sweetwater

County, Wyo., by A. R. Schultz 282

Coal of the Denver Basin, Colorado, by G. C. Martin 297

The South Park coal field, Colorado, by C. W. Waahbume 307

The Colorado Springs coal field, Colorado, by M. I. Goldman 317

The Canon City coal field, Colorado, by C. W. Waahbume 341

The Trinidad coal field, Colorado, by G. B. Richardson 379

Isolated coal fields in Santa Fe and San Miguel counties, New Mexico, by

J. H. Gardner 447

The C*carthage coal field, New Mexico, by J. II. Gardner 452

The coal field between San Mateo and Cuba, New Mexico, by J. H. Gardner. 461 Petroleum and natural gas:

Geology and oil prospects of the Reno region, Nevada, by Robert Anderson. 475 Two areas of oil prospecting in Lyon County, western Nevada, by Robert

Anderson 490

Analysis of crude petroleum from Oklahoma and Kansas, by T). T. Day... 494

The Madill oil pool, Oklahoma, by J. A. Taff and W. J. Reed 504

Development in the Boulder oil field, Colorado, by C. W. Washbume 514/

The Florence oil field, Colorado, by C. W. Waahbume 517

Survey publications on petroleum and natural gas 545

Index 5-19

Illustrations.

Page.

Plate I. Map of Washburn lignite field, North Dakota 22

II. Map of Fort Berthold Indian Reservation lignite field, North

Dakota Zi

III. Map of Fort Peck Indian Reservation lignite field, Montana 54

IV. Map of southeastern part of Bull Mountain coal field, Montana 72

V. Map of northwestern part of Bull Mountain coal field, Montana 72

VI. Map of Milk River coal field, Montana 98

VII. Map of northern part of Custer National Forest, Montana, with stratigraphic sections 110

VIII. Map of the Powder River coal field, Wyoming, adjacent to the Burlington Railroad 130

IX. Columnar sections, Buffalo coal field, Wyoming 154

X. Map of Buffalo coal field, Wyoming, showing sections of coal beds.. 168

XI. Map of T. 43 N., R. 79 W., Wyoming 168

XII. Map of coal field in the southeastern part of the Bighorn Basin,

Wyoming 180

XIII. Map of eastern part of the Little Snake River coal field, Wyoming.. 210

XIV. Map of the southern part of the Rock Springs coal field, Wyoming.. 240 XV. Map of the Rock Springs coal zone in the southern part of the Rock

Sprinji:8 coal field, Wyoming 280

XVI. Map of South Park coal field, Colorado 314

XVII. Map of Colorado Springs coal field, Colorado 334

XVIII. Map of Canon City coal field, Colorado 370

XIX. Diamond-drill records, Trinidad coal field, Colorado 394

XX. Map of Trinidad coal field, Colorado 426

XXI . Map of Carthage coal field, New Mexico 456

XX 11. Map of coal field between San Mateo and Cuba, New Mexico 472

XXIII. Geologic map of vicinity of the Madill oil pool, Oklahoma 504

XX IV . Well map of the Florence oil field, Colorado 534

FiouKE 1. Index map showing location of Washburn, Fort Berthold Indian

Reservation, and Fort Peck Indian Reservation lignite fields,

North Dakota and Montana 19

2. Sketch map of Big Sandy district, Milk River coal field, Montana. 102

3. Sections showing similarity in the arrangement of the coal-bearing

part of the Laramie in the Colorado Springs field and in the Denver Baiin, (\)lorado 333

4. Swtion of cliffs 4 miles north of Trinidad, Colo 388

5. Sills of igneous nx-k in Laramie" formaticm and ])ed of natural

coke 391

6. Secticm of coal near Di'lagua and Hastings, Colorado 410

7. Faulted coal bods, Midway mine 413

8. Fault in Berwind mine 413

9. Solution in Pictou mine 415

10. Section between Occidental and Oakdale mines 418

11. Section at Occidental mine 419

12. Section between Cuatro and Tercio, Colorado 422

13. Map of T. 5 S., R. 5 E., showing location of wells drilled in vicinity

of Madill, Okla 512

14. Geologic sketch map of the Canon ( 'ity embay men t 518

15. Diagram showing drilling success of United Oil Company in

oil field, Colorado, 1887-1908 534

Contributions To Economiqseology,

1908, Part Ii. ,,.

Mineral Fuels.

Marius R. Campbell, Geologist in Charge.

Introduction.

By Marius R. Campbell.

During the year 1908 considerable progress was made by the United States Geological Survey in the study of the mineral fuels of the country. This included the examination of a number of coal and oil fields and also some work on the quality of the fuel and the best method of its utilization. Complete and detailed reports covering this work will be published as soon as the investigations of a particular field have been completed, or as soon as the problems of correlation, development, and utilization have been solved. In the meantime brief, preliminary statements have been prepared by the men engaged in the work, embracing most of the points of economic importance, and these have been assembled into the present volume, which is conformable with Bulletins 316 and 341. It is hoped that by this method of publication the public may receive at an early date the results of work done by this Survey, in order that the mineral resources of the country may be developed to the fullest extent compatible with legitimate demand and supply and a due regard to the conservation of these resources for future generations.

In the conduct of the field work on which these reports are based, two objects have been particularly prominent and have governed the character of the investigations: These are (1) the examination of the land for the purpose of classifying it as to its mineral or nonmineral character and, in the case of coal land, of determining its

6 Contributions To Economic Geology, 1908, Part Ii.

selling value; and (2) a general" investigation of the scientific questions involved in any particiilaiF. field and the determmation of its commercial value and th 4eSjt fnethod of development.

The first or dominant'JW?tbr was the determination of the character

and the valuation- oY'ihe' public land. These determinations were

made wholly for. tite. use of the Government itself in disposing of its

mineral land. "The second or general investigation of the mineral

resource'jof the country was made for the benefit of the public at

large.afriHhe results of this work are embraced in the series of reports

of.wfiteh'this volume is one. The order in which the fields are exam-

.'iuett depends entirely on the needs of the Government in disposing

.; (iris land now on the market, but in general the more important

'fields in the public-land States have been examined first.

The work has been done under the general direction of the writer, who has been most ably assisted in the coal work by Cassius A. Fisher and all the men engaged in the work. It is impossible to enumerate the services performed by each man, but the success of the work has been due to the individual efforts of every member of the force and also to the hearty cooperative or team work without which it would have been impossible to carry on the work successfully. Although economic questions had to be given prominence, the wTiter wishes to congratulate each geologist on the amount of scientific data which have been accumulated and on the permanent value of the results and their bearing on the vexed question of the stratigraphy of the American Mesozoic and Tertiary rocks. The writer desires particularly to acknowledge his indebtedness to T. W. Stanton and F. H. Knowlton, who have so ably assisted in field and office in collecting and interpreting the fossils associated with the coal beds. This work has been invaluable, for without it the tangled problems of correlation and stratigraphy could not have been solved.

For forty 3ears the age of the coal-bearing rocks of the Rocky Mountain States has been in dispute, and while it can not be claimed that the question is settled, still the Survey's systematic examination of the coal fields during the last three years, in connection with the classification of the lands, has gradually brought order out of chaos. Now the end seems to be nearly in sight, and it is confidently believed that a few years' work will completely solve this perplexing problem.

Necessarily, the classification and valuation of coal land presupposes a careful study of the coal itself to determine its physical and chemical properties and its heating value. In order to make such a study, samples have been collected from all the fields examined and either proximate or ultimate analyses made in accordance with regulations adopted by the American Chemical Society, the highest authority in this country. Sampling was done systematically and uniformly, and it is believed that the resulting analyses will be

Introduction. 7

accepted as representative of the coals of the various fields. No other organization can carry on analytical chemical work so extensively and impartially, and the results should become the standards not only for buying and selling coal, but also for buying and selling coal land. The coal analyses already made by the United States Geological Survey number many thousand, and all of these are strictly comparable, except in a few cases, where weathered coal not typical of the bed or of the field was included in the sample. The analyses contained in this volume are published for the first time and they constitute an important addition to the mass of data already available regarding the composition and relative values of American coals.

y

Coal And Lignite.

Stratigraphy And Coal Bkds Of The Indiana

Coal Field.

By George H. Ashley.

Introduction.

In 1898 the State Survey of Indiana published a detailed report on the coal deposits of that State. In the years between 1898 and 1908 the coal industry of the State expanded greatly, several hundred new mines having been opened and literally thousands of drillings having been put down. The result of this work was to multiply greatly the available knowledge of the coal measures, as well as to show the existence of errors in the earlier report. In cooperation with the State the United States Geological Survey therefore made a reexamination of the area of development in 1908, the work being done by the writer with the assistance of E. F. Lines. The economic results will be published by the state geologist of Indiana, W. S. Blatchley, in his annual report for 1908. The scientific results will be published by the United Stated Geological Survey in a future report on the Eastern Interior coal field. The present paper is a brief preliminary general account of the stratigraphy and coal beds of the Indiana coal field.

The Indiana Coal. Field.

The coal measures of Indiana lie in the southwestern part of the State, extending from Warren County on the north to Ohio River on the south, and eastward to a northwest-southeast line running from Warren County to Perry County. They cover practically all of sixteen counties and parts of nine additional counties. The Indiana field is part of the Illinois coal basin, or the Eastern Interior coal region. This region has a true basin shape, being deepest in the center in southeastern Illinois and rising to a rim on all sides. The Indiana

10 Contributions To Economic Geology, 1908, Pabt Ii.

field is a part of the eastern or northeastern rim, extending in the southwest corner of the State well into the center of the basin.

The coal measures have a total thickness of approximately 2,000 feet, of which about 1,300 feet occurs in Indiana. Of this 1,300 feet there are 600 feet of barren beds at the top, then a 500-foot interval which contains most of the workable coals, followed in descending order by 200 feet or more of rocks consisting mainly of sandstone. Recent work of David White indicates that the rocks of the* upper 600 feet are of post- Allegheny age, those of the next 450 feet of Allegheny age, and the lower rocks of Pottsville age.

The Coal. Beds.

Occurrence.

Coal occurs at about thirty-four different horizons, of which about twenty-five have a fairly wide persistence. Of these beds one is workable nearly everywhere in the State where it outcrops and eight others are workable over large areas. Several of the smaller beds are workable locally. The average thickness of all the beds of the State is probably less than 2 feet, but the workable beds range from 3 to 8 feet. The most important bed in the field probably averages 5 feet within its outcrop, and over large areas averages 6 to 8 feet. Many of the other beds average 6 to 8 feet over several hundred square mils, but are thin or absent over adjacent areas. The maximum thickness measured was 10 feet 2 inches, though thicknesses of 11 to 15 feet are reported in swamps.'

A few individual coal beds can be traced the whole length of the Indiana coal field. In one case this tracing appears to be thoroughly reliable, and in several others it is apparently good, though the possibility of error must be admitted. Still other coal beds can be traced with only a fair degree of probability. On the other hand, beds which maintain a thickness of 6 or 8 feet over large areas thin out within the space of a few miles. In some beds such thinning out is against the edge of its basin, and though the horizon of the coal can be traced for miles no further indication of coal can be seen within the State. In other beds the coal is very regular over large areas and very irregular over similarly large areas beyond.

In general the upper beds are much more regular than the lower beds. In fact, the lowest beds occur in small, nearly detached basins, usually lying in a west of north and east of south direction and ranging from a few acres to several square miles in extent. In the center of one of these basins the coal may have a thickness of 5 feet, but between the basins on the ridges the thickness may decrease to as many inches. In thes basins it is observed that where the coal has

Indiana Coal Field. 11

several benches the lowest benches thin out first in approaching the rise, so that the coal going over the divide into the next basin may represent only the upper part of the top bench. Of even more interest is the fact that at two horizons where the coal in the basins has a somewhat distinctive section, the same section is repeated from basin to basin over hundreds of square miles.

Names Of Coal Beds.

Probably no coal field in the United States of ecual size has been studied so completely and is now so well known as the Indiana field. One result of this study has been to show that as a rule thick or workable coals are found at only a few horizons. These horizons have been designated by Roman numerals from II to VII. Intermediate coals have been named by the addition of a small letter to the name of the first principal coal below. Thus the rider of coal V is coal Va; the still higher thin coal would be Vb, etc. Coal II is the lowest of the coals that David White has thought will prove to be of Allegheny age. To the underlying coals, thought by him to be of Pottsville age, local names have been given.

Type Section Of Coal Beds.

One of the interesting things that have been emphasized by the results of recent drilling is the tendency of the coals in Indiana to reach their best development midway between the north and south boundaries of the field. Thus, several coals that are 6 to 8 feet thick in Sullivan, Greene, Clay, and Vigo counties are thin or lacking toward the north and south ends of the coal field and, with possibly one exception, all the workable coals of the State are workable in that area. The coals from coal III to coal VIII are best known in Sullivan and Greene coimties, where each of the numbered beds ranges from 4 to 8 feet in thickness, with sections so distinctive that they can hardly be confused, and where about four hundred detailed sections, many of which show every foot of rock from coal III up to coal VIII, help to make the stratigraphy quite clear. Though considerable drilling has shown the relation of coal III to all the lower coals in Greene County, they are still better known in northeastern Vigo and northern Clay counties.

The portion of the following section from the Merom sandstone to coal III is therefore taken in Sullivan County and the portion from coal III to the Lower Block coal in northeastern Vigo and northem Clay counties. The beds above the Merom sandstone are best exposed in Gibson County.

Contributions To Economic Geology, 1908, Part Ii.

Type section of coal measures in Indiana.

Oibmn Omntf.

Sandstone .'

Shale, etc., with 6 inches local coal

Suidstone, hard bedded

Shale, partly covered

Shale,sandy

Shale, blue and argillaceous

Limestone, soft and shaly to very hard

Aldrichcoal

Shale, coaly

Sandstone (sandstone of Mansfield HiUs, etc.) .

Limestone, hard, gray, and fossUiferous

Shale, black

Friendsville coal (0-4 feet).

Clay.

Sandstone, upper part massive (sandstone of Gordon Hills) .

Limestone or calcareous and fossiiiferous sandstone

Shale, black

Parker coal. Shale.

Sandstone. Shale.

Sandstone, soft, and sometimes shaly.

Clay shale, bluish

Sandstone, shaly

Shale

Top of Inglefield (Merom?) sandstone.

Menm, SuUivan County. Sandstone, Merom .

"Productal" limestone, rich in fossils.

Shale, calcareous

Shale, dark, bituminous

Coal , rash.

Fireclay.

Clay shale, dark

Sandstone, coarse, hard

Limestone, crlnoidal, shelly.

Place of coal Villa (?).

Fire clay

Sandstone, flaggy

Shale, drab, with large iron nodules

Shale, gray, with pyritous partings

Sandstone, quarry

Clay shale, hard, siliceous

Clay shale, siliceous, with large iron nodules

Clay shale, liKsolored, with small round iron nodules.

Coal VIII,

Sullivan and Oreene eounttet in general.

Clay

Limestone. Shale

Sandstone

Shale

Sandstone, shaly.

Coal VII (3-C feet).

Clay

Limestone

Shale

Sandstone

Shale

Coal VI (5-9 feet).

Clay.

Coal

Shale

Sandstone. Shale

Thickness of beds.

Feet.

Total thickness.

Feet.

69)

I

- !

23

415)

5:15

Indiana Coal Field.

Type section of coal measures in Indiana — Continued.

SulUvan and Greene counUeM in yrfieroZ— Continued.

Clay

Sandstone... Shale

Limestone

Sbale, black, sheety, with pyrite concretions.

Coal V (0-11 feet).

Clay. Limestone. Shale

Sandstone. Shale

Limestone

Siale, black, sheety.

Clay

Sandstone, shaly.

Coal IV (4-6 feet).

Sandstone

Shale

Limestone

Shale, black, sheety

Coal Ilia.

Clay. Shale.

Clay.

Coal III (0-13 feet).

Coal.

NorihauUm Vigo Countf and northern Clay Cminty.

Clay. Shale.

Clay

Shale

Sandstone. Shale

Coal.

Clay

Shale

Sandstone. Shale

Limestone

Sandstone, shaly.

Coal.

Shale

Coal II (0-4 feet). Clay.

Limestone.. Shale, black.

Coal, Mlnshall (0-6 feet).

Clay

Shale

Sandstone. Shale

Coal, upper block (0-5 feet).

Clay

Shale

Shale, sandy fake")

Coal, lower block (0-5 feet) . Clay.

Sandstone, Mansfield, replaced with shale at many places in the basin. Shale

Coal...

Clay

Shale

Top of lower Carboniferous.

Thickness of beds.

Feet.

Total thickness.

Feet.

Ig

2J

U

969$

l,a')2| 1,054

1,066

Contbibuiions To Ecomomic Geology, 1908, Part Ii.

The above section does not include the uppermost members in Gibson County nor the lowest members in the southeastern part of the field.

To give a better idea of the relation of the intervals between the different coal beds and the relative thickness of these beds in different parts of the coal field, the following table is inserted :

InUmtU and Ihietriesi, i

'fat, of principal coah coalfield.

I number of poinU o

Is 1

g

J

Is

s"'

dil !t h

INDIvmOAL COAL BEDS.

In discussing the coals it is convenient to take coat V as u base horizon. It is a thick coal with certain peculiarities of roof which render its recognition possible through the whole length of its outcrop in Indiana. It is at almost every point characterized by a of black sheety shale, the under surface of which contains pj-rite concretions that, as a rule, project downward into the conl. In simie mines these concretions are vorj- abundant, the roof being botryoidal from thoir presence. In other mines they iire only scattered, possibly one or two to a room, but tlioy are absent in few of the mines. Some of them project down into the coal as much as 4 or 5 feet. Overlying the black shale is a limestone. Similar black shales overlie other coals and are in turn overlain by limestones, but these coals are almost invariably thin, the accompanying limestone is usually thin, and the presence of the pTite concretions is not everywhere obvious. There is only one other coal, lying about .300 feet stratigraphically below coal V, whose overlying limestone is thick at

Indiana Coal Field. 15

many places and which is itself of workable thickness. Its position so far below coal V, however, insures its outcropping well to the east of the outcrop of that coal, so that, although the two have often been confused in the past, there is no danger, with the present knowledge of the coal field, of their being taken for the same coal. Coal V has a thickness of 4 to 10 feet, averaging from 5 to 8 feet over a large part of the area within which it outcrops and maintaining this thickness with considerable uniformity from southwestern Vermilion County, where it enters the State, to Ohio River.

About 70 feet above the top of coal V, in SuUivan County, lies coal ranging in that county from 6 to 8 feet in thickness. Practically everywhere it is divisible into four benches — an upper bench of about 2i feet, a thin bench of 4 to 6 inches, a lower bench of about 2i feet, and a bottom bench of 1 foot. The two main benches range from 2 to 2J feet or more. Between these benches occur gray-shale partings that are nearly everywhere half an inch thick. When exposed to the atmosphere in the entries of the mines this gray shale ' weathers to a white clay, so that in the mines on this coal bed there appear to be two white chalk marks about midway of the wall at every point. Practically no doubt can therefore exist as to the correlation of this coal within that district. The bottom bench of 1 foot is bony and is usually left in the mine. At the north edge of Sullivan County this coal becomes irregular, in places appearing to run out entirely, and north of that point neither drilling nor mining finds any trace of it in Indiana. It appears to maintain its thickness south of Sullivan County as far as Bicknell and for several miles farther south, though it becomes broken up toward the southwest. From that locality southward it disappears as a regular bed, in many places being entirely absent and in others appearing as a thin bed of 1 or 2 feet. It reaches a workable thickness in a few localities and is commercially worked at two points in Gibson County. Apparently it approaches nearer and nearer to the overlying coal toward the south, until the two range from 20 feet to 6 inches apart, and in at least one place the two coals have been mined together. It will be discussed further in connection with the occurrence of coal VII, in the southern part of the State.

About 40 feet above the top of coal VI in Sullivan County comes coal VII, which is practically everywhere a solid coal from 3 to 6 feet in thickness, overlain by shale or sandstone. North of Sullivan Coimty this bed is readily traced past Terre Haute and through the southwest comer of Vermilion County out of the State. West of Terre Haute and to the north it shows a thickness of 4 to 5 feet of good coal, overlain by 1 to 2 feet of bony coal. A few feet below this coal, in all of the northern part of the coal field, is a limestone

16 CONTRIBUTIOirS TO ECONOMIC GEOLOGY, 1908, PART II.

that is believed to be one of the persistent members of the coal measures. South of Sullivan County this coal bed can be traced through Wheatland, in the hills west of Petersburg, and on to Ohio River, with a thickness of 4 feet or less, becoming rather thin as Ohio River is approached. As stated above, the underlying coal VI is close beneath it from Gibson Coimty southward, and in one place in western Warrick County they are worked together. In general the Umestone below coal VII lies between the two coals, and in many places where the two coals are close together the limestone forms the only parting. This condition continues into western Kentucky, where coal VII is known as Kentucky 12 and coal VI as Kentucky 11. Coal V of Indiana corresponds to coal 9 of Kentucky.

Above coal VII in Indiana, as a rule, only thin coals are foimd. In a few places these coals reach a thickness of 3 or 4 feet, but in nine out of ten drillings they show thicknesses of less than 2 feet, and commonly less than 1 foot. Small coals occur between coal V and coal IV, and though in some places they reach a thickness of 3 feet, as a rule they are thin, and in the presence of much thicker coals above and below they will not be considered of workable character for a long time.

Coal rV, the bed extensively worked around Linton, is from 100 to 130 feet below coal V. It is commonly a solid coal, with a sandy shale or sandstone roof and a sandstone or sandy clay floor. It shows a tendency to split in many districts, the splitting being in places rather extensive, so that the benches are separated by 10 to 15 feet or more. It can be traced northward to Seelyville, where it is the surface bed, ranging from 3 to 6 feet in thickness, and on to the horseshoe bend of Little Vermilion River, being of workable thickness nearly everywhere, except as it may be broken up by one or more large partings. It is a coal of excellent quality. To the south the thickness of this coal is somewhat less, usually not being more than 3 J feet and toward Ohio River averaging probably less than 2i feet. In that district it is nearly everywhere a solid coal, with either a shale or a sandstone roof.

About 70 feet below coal IV in Greene County is coal III, a bed 6 to 8 feet thick, almost invariably with one or more regular partings. It maintains this thickness northward through western Clay County and eastern Vigo County, being the large bed worked around Turner and Stanton and the principal bed at Seelyville, Fontanet, and Rosedale. It tends to be a strong steam coal, but in many places has a high content of sulphur. In the Rosedale-Fontanet district the sulphur occurs in the form of one or more regular partings and therefore is more easily separated. North of Coxville this bed occurs in scattered patches for a distance of 6 or 8 miles, beyond which it is

Indiana Coal Field. 17

absent altogether. South of Greene County no bed of this character is found, and it is possible that the coal runs out entirely. In many places one or more thin coals are found about in the position of coal III, and it has been assumed that they may possibly represent this coal. Few of these thin coals south of Greene County, however, are workable, though here and there they increase to 3 feet in thickness. The coal called the Rock Creek coal in the Ditney folio possibly belongs at the horizon of coal III of Greene County.

About 100 feet below coal III in northeastern Vigo County is a coal bed that is being worked around Fontanet, Minshall, and Mecca, and at other points. It has been called in the trade the Minshall coal, and this name has been retained for it, as it comes below the bed called coal II in the general columnar section. It is a coal of variable thickness, lying in basins and ranging from 5 feet to a fraction of an inch. Overlying it in many places is black shale, which is not everywhere sheety, and above that a heavy limestone. A limestone underlain by a coal that is in some localities of workable thickness occurs at many points through the northern part of the Indiana coal field in Parke, Fountain, and Warren counties. It has been assumed to belong at the horizon of the Minshall coal. In the Brazil district of Clay County this bed has been called the Rider Block coal, as it lies only about 30 feet above the Upper Block coal.

In the Brazil district the two block coals lie about 30 feet apart. Each may have a thickness of about 5 feet in the center of the basins and thin down to a few inches on the hills between the various basins. The Upper Block coal has slightly the greater thickness. It is usually a solid coal, with a 2-inch band of brittle coal a little below the middle. It is also distinguished from the Lower Block coal by the fact that the vertical joints that characterize both the block coals are in the Upper Block coal more open at the top and are indistinct below this brittle "bench mining.*' The Lower Block coal is a solid coal except for a smooth parting 6 to 10 inches from the top. The coal above that parting is not of the block character. The joints are more open at the bottom and, as a rule, do not penetrate this upper bench of coal. In the center of the basins below the main bench there usually occurs clay, then 1 to 2 feet or more of bony coal, then, locally, up to 2 feet of good coal, with clay underneath. Toward the edges of the basins these underlying benches thin out one at a time, beginning at the bottom, and at the crest of the divide even the lower part of the main coal has thinned out, leaving possibly only the thin upper bench to pass over to the next basin. The two block coals can be traced northward into Fountain County, though the Lower Block appears to be absent in Warren County. The block coals extend southward with their characteristic features into

7963°— Bun. :i8l— 10 13

18 Contributions To Economic Geology, 1908, Part Ii.

southern Clay County and central and eastern Greene County. South ot tnat region their characteristics have not been recognized, and correlations made with them are only suggestional in character. Through Daviess, Pike, Dubois, Warrick, Spencer, and Perry counties a large number of coals are found, but no extensive drilling and relatively little mining have been done, so that the correlation of these coals from point to point is very uncertain. Furthermore, the fact that they occur in basins, like the coals of corresponding position to the north, means that at many points where they appear they may be only a few inches thick and not recognized as the same coal that may be opened by a country bank a few hundred yards awav. The fact that the coal on the divides between the basins ranges from 20 to 50 feet higher than the coal in the center of the basin also confuses any attempt at correlation on the meager information at present in hand. In some areas it has been possible to make correlations for short distances. For example, a coal that is overlain by limestone and that lies about in the position of the Minshall coal in the northern part of the State and was called the Holland coal in the Ditney folio has been recognized on Sugar Creek, in southeastern Daviess County; over a considerable territory south of Wliite River, north and south of Holland, in Dubois Cxjunt}'; and around Buffaloville and Newtonville, in Spencer County. Although present knowledge of the coals of these southern counties does not seem to hold out hope of a laie coal output, it is quite possible that the coals there, when better known, may show the presence of as much coal in this part of the section as is found in Clay or other more northern counties. In the southeastern part of the coal field is a coal that has long extensively workeil at Cannelton, from which it has been calleil the Cannelton coal. Like the other coals, it iKcurs in basins, ranging where present 4 feet in thickness down. It has Inon recognizetl along Andersin River, as far north as St. Meinrad. Il is possible thai il is the same coal that locally shows a workable thickness anund Shoals.

Tiik Washburn Lignite Field, North Dakota.

By Carl D. Smith.

Introduction .

The Washburn field, a small part of a laie area of lignite-bearing rocks of Tertiary age which covers the western half of North Dakota, comprises parts of McLean, Oliver, Mercer, and Burleigh counties

and lies a short distance to the southwest of the center of the State, 40 miles up Missouri River from Bismarck. (See fig. 1 .) The investigation of this field was undertaken primarily to obtain information

20 Contributions To Economic Geology, 1908, Part Ii.

regarding the character, depth, and horizontal distribution of Hgnite beds within reach of irrigable lands along Missouri River, which it is proposed to water by pumping, with lignite as fuel.

That part of the field east of Missouri River is traversed by a branch of the Minneapolis, St. Paul and Sault Ste. Marie Railway. A projected branch of the Northern Pacific Railway, leaving the main line at Mandan, follows closely the west bank of the Missouri through the field. At certain seasons the river furnishes transportation to and from the region.

Acknowledgments are due to Mr. Jay W. Bliss for his able assistance in the field work, and to Mr. T. R. 'Atkinson, state engineer, for additional notes and data concerning lignite near Wilton.

Topography.

The field is mainly a smooth, rolling prairie with bluffs and badlands here and there along the larger streams. The elevation of the water surface of the Missouri at ordinary stage at Washburn is 1,656 feet above sea level. Away from the immediate valley of the Missouri the general elevation averages from 200 to 350 feet higher than the river.

The presence of glacial material left by the retreat of the great ice sheet, which covered this part of the State in comparatively recent geologic time, has no doubt had a tempering effect on the topography. In other parts of the State, beyond the limit of glaciation, where conditions are otherwise similar to those around Washburn, badlands topography is common along the larger streams. Although the direct effects of glaciation are not now apparent, probably on account of the softness of the local formations and the consequent rapid weathering, indirect results appear in numerous intermittent lakes and abandoned stream channels.

Geology.

Stratigraphy.

All the stratified rocks described here belong to the Fort Union (early Eocene) formation. In the past these rocks have been generally referred to the Laramie (Cretaceous), but later work in the region has proved that they are Tertiaiy. The formation consists of sands, clays, and sandy days, in about equal proportion in alternating layers, with beds of lignite scattered throughout. The days and sandy clays are usually dark gray or somber in color; the sands and sandstones vaiy in shade from light blue to buff. All of this material, except local sandstone lenses and irregular sandstone layei-s, is soft and weathers rapidly.

Overlying the Fort lnion formation is a mantle of glacial drift, varying greatly in thickness and made up of a variety of materials

WASHBUBN LIGNITE FIELD, NORTH DAKOTA. 2l

foreign to this general region. It is usually covered by soil, but- in places erosion has tended to segregate the bowlders at the bases of step slopes or has partly swept away the soil, thus leaving the bowlders on or near the surface. They vary in size from mere pebbles to masses several feet in diameter and are used principally for building foundations.

Structure.

So small an area was covered by this investigation that little can be said of its structure. Evidence now in hand, however, indicates that there is a slight dip of the formations toward the east, probably not more than 2 feet to the mile. This is inferred from the fact that a bed" of lignite, which is low in the section on the west side of the field dips beneath the river toward the east. So far as mining is concerned the lignite beds and containing formations may be regarded as lying flat.

The Lignite.

General Statement.

By reference to the columnar section on the map accompanying this report (PI. I) it will be seen that workable beds of lignite occur at six horizons in the 315 feet of strata lying above river level. The exact relation of the beds mined at Wilton to those about Washburn is not known, but it is thought that they are slightly higher. No records of deep wells in this area have been obtained, hence it is impossible to say anything positive concerning lignite beds that may underlie the field at greater depths than river level. It is probable, however, that many workable beds of lignite could be found to a depth of 1,500 feet.

Heretofore the lignite beds of this general region have been described as lenticular and impossible of correlation for distances exceeding 2 or 3 miles. It is true that the lignite varies considerably in thickness from point to point, but the term 'lenticular" is misleading and considerable work in this general field has proved that some of the more important beds can be correlated or even traced in their outcrops for much greater distances than 2 or 3 miles.

Many outcrops of lignite beds, covered by glacial material or talus, are marked by springs and seepages. Beds of lignite seem to be the best carriers of underground water. This is probably due to the variable character of the sands and clays which make up the section. Although a formation at a certain horizon may be in one place a porous sand well adapted to carrying water, its character may so change within a short distance horizontally that water can not find its way through. In this way the lignite beds, which are fairly homogeneous in texture and more persistent laterally than other formations, become the water-bearing beds.

The accompanying map (PI. I) shows the locations of the principal mines and prospects in the field, with a columnar section indicating the vertical distribution of the various beds of lignite. This section was compiled from widely separated exposures, and it is not to be assumed that fuel will be found at a given elevation in all parts of the area.

It is quite probable that a number of lignite exposures and mines not represented on the map are to be found in the field. As few townships as possible have been used to show the general connections of the different districts discussed and the positions of the railroads. Hence, if any mines in the field are not here discussed, the omission is due not to oversight but to lack of time in which to visit them.

Detailed Description Of Lignite Exposures.

A few representative detailed sections of lignite beds in the area covered by this report are given in the following pages.

Old Coal Harbor District.

Joe Mann mine. — At the base of the bluff in the NW. sec. 34, T. 147 N., R. 84 W., lignite is being mined at present. The method used is a combination of stripping and drifting.

Section at Joe Mann mine.

Clay roof. Ft. in.

Lignite 2 10

Clay 6

Lignite 4 6

Clav, eandv I 2

Lignite 2 5

Total lignite 9 9

Both up and down the river from this locality the lignite has been burned along its outcrop, producing a red clinker. A short distance north of the mine the lignite is on fire at present. Its horizon lies from 15 to 30 feet above water level at ordinary stage. The fuel is mined for local neighborhood use and is delivered by wagons.

KsJces mine. — About 1 mile southwest of the Joe Mann mine, in the NE. i sec. 4, T. 146 N., R. 84 W., Eskes & Son are stripping a bed of lignite in the face of the bluff, 50 feet above the bod at the Joe Mann mine.

Section at Kshes mine. Clay Ft. in.

Clay and lignite 2

Lignite 2 (I

Total lignite 5 1

t

z

t

R.79W.

Y

iiv,

nt

"

/

-[

:

o

/

--'

/

r

U

"

if

R.

9W.

WA8HBUBK LIGNITE l?imJ>, NORTH DAKOTA. 23

The outcrop of this bed can be easily followed to the south for 4 or 5 miles. At several places it has been stripped and is marked by a fringe of clinker, having been burned. The bed is extremely variable in tliickness, its position in the section at other localities being occupied by bituminous clay or thin, valueless seams of lignite.

Marion mine, — In the SW. i sec. 26, T. 145 N., R. 84 W., an entry has been driven on the Joe Mann bed of lignite, which is easily traceable from the Joe Mann mine southward to the Marion mine by the clinker produced by burning along its outcrop. The section at the Marion mine shows 7 feet 9 inches of lignite, with clay roof and clay floor.

About one-foiu'th mile south of the Marion mine another entry is being driven on the same bed, the thickness being about the same.

A short distance south of these openings the outcrop of this bed of lignite, as marked by the clinker, disappears below the lowland bordering the river, and was not seen again in the field.

The writer did not visit the region west of the river opposite the points mentioned above. F. A. Wilder* gives the following measurements of beds seen along the bluff from Mannhaven to Stanton:

Section near Mannhaven.

Feet.

Lignite, good 6

Clay 2

Lignite 1

Clay 1

Lignite, good 2

Clay 10

Lignite, good 8

Sand to river level 10

Total lignite 17

Wilder states that this section may be seen for 2,000 feet along the river.

Section .V or 4 miles south of fannhavcn,

Ft. in.

Lignite 3

Clay 6

Lignite 3

Clav 2

Lignite 3

Total lignite 9

This bed probably represents the upper part of the section at Mannhaven.

According to Wilder a T-foot bed outcrops near river level at the edge of the flat 2 miles above Stanton. This bed doubtless cor-

aThfi lignite of North Dakutu and its rolutlon to irrigation: Watrrr-Supply U. 8. Ocol. Survey No. 117.905.

24 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1908, PaM 11.

responds to the bed seen by the writer at the Marion mine, east of the river, opposite Stanton.

Washburn District.

Pfister dk Cramer mine. — At an elevation of 250 feet above river level, in the NE. i sec. 36, T. 145 N.. R. 83 W., Pfister & CYamer are mining a bed of lignite by stripping. The bed measures 6 feet thick, but the upper feet is weathered and worthless.

Satterlund mine, — At an elevation of about 180 feet above the level of Missouri River occurs a bed of Ugnite, which is for convenience of reference called the Fairman bed. It is exposed at a number of places about Washburn. The Satteriund mine, in the NE. i SE. i sec. 1, T. 144 N., R. 83 W., is probably on this bed.

Section at Satterlund mine. Clay roof. Ft. in.

Lignite 7

Clay i

Lignite 2

Clay 3

Lignite (thickness reported) 1 6

Total lignite 10 6

The cover above the lignite is here 25 to 40 feet thick. The mkie is operated by a drift 400 feet in length, and its output amounts to 30 or 40 tons a day. The product is consumed by residents of Washburn and vicinity.

Phippen mine. — Northeast of the Satterlund mine, in sec. 35, T. 145 N., R. 82 W., lignite is being taken out at present by stripping. The mine is known locally as the Phippen mine, and is probably in the same bed as the Satterlund. At the time this mine was visited only the lower part of the bed could be seen. A section of the part of the bed exposed shows 5 feet 4 inches, including two partings.

Section at Phippen mine.

Debris roof (top of bed not eeen). Kt. in.

Lignite 8+

Clay 4

Lignite 2 8

Clay 5

Lignite 1 3

Total lignite 4 7 +

Lignite is mined here to supply local demands, and is variously reported from 6 to 14 feet thick. A considerable area about the mine is underlain by this bed, but the cover is relatively light.

On the point of the hill west of the wagon road, in sec. 8, T. 144 N. R. 82 W., an opening has been made at the horizon of the Fair-

Washburn Lignite Field, North Dakota. 25

man bed, 180 feet above river level, but the lignite was found to be replaced by several feet of carbonaceous clay, or black jack.''

In the river bluff south of Conklin the stratigraphic position of the Fairman bed is occupied by two thin beds separated by a large parting. The lignite is here burned along its outcrop for several miles and may be locally workable. Near old Coal Harbor the horizon of the Fairman bed is occupied by thin, worthless seams of lignite.

Old Fairman mine. — Lignite at the old Fairman mine, in the NE. i sec. 27, T. 143 N., R. 81 W., shows a thickness of 7 feet of apparently good coal, with two thin partings.

Section at Fairman mine. Clay roof. Ft. in.

Lignite 1 3

Clay 6

Lignite 1 6

Clay 3

liignite 3 6

Total lignite 6 3

Due south of the old Fairman mine, in sec. 3, T. 142 N., R. 81 W., is a partial exposure of a bed of lignite at the same elevation, which is taken to be a continuation of the Fairman bed. Its thickness at this locality could not be measured.

Between the Fairman bed and Missouri River level, in the Washburn district, no lignite of any consequence has been observed. A bed 75 feet above water level has been mined by Mr. Petersen at his house, in sec. 24, about 1 mile southeast of Washburn. The bed here varies in thickness from 1 i to 2 feet and is underlain by 4 feet of "black jack'* or bituminous shale. In a small draw which runs southward through sec. 8, T. 144 N., R. 82 W., a number of seepages indicate that one or two beds of lignite, probably thin, are to be found about 50 feet above river level.

District South And West Of Missouri River.

Van Epp mine. — A bed of lignite that corresponds in elevation to the Fairman bed is mined by stripping in the SE. J sec. 10, T. 143 N., R. 82 W., 3 miles south of Hensler post-oflice. The bed is 6 feet 4 inches thick, without partings. One mile northwest of tliis opening are two others, one in sec. 10, the other in sec. 9, both of which show 6 feet of clean, hard lignite. Tliese are doubtless on the same bed as the Van Epp mine.

Old Cogan and other mine. — About 6 miles west of the abovementioned locality, in the SE. i sec. 8, T. 143 N., R. 83 W., a bed of lignite at the same horizon was formerly mined by stripping at the Cogan mine, but the workings have been abandoned and have caved

S6 CONTBIfiua?10N6 TO ECOKOMlO GEOLOGY, 1908, PAitT 11.

in. The bed measures 3 feet 10 inches and is very hard and free from partings. . About 1 mile east of Cogan's mine, near the middle of sec. 9, an opening on the same bed shows a thickness of 3 feet 9 inches. Fuel is mined here for local use.

In the SE. J sec. 2, T. 143 N., R. 83 W., a bed of lignite 100 feet above Missouri River is mined for local use. The bed is 4 feet 4 inches thick, with a 2-inch parting 4 inches from the bottom.

Along the gulch which runs northward through sees. 17, 8, and 5, a short distance west of Cogan's mine, lignite varying in thickness from a few inches to feet outcrops in manj" places.

Along an eastward-flowing stream in the northern part of sec. 7, T. 142 N., R. 81 W., Ugnite is being mined for local use from three small strip pits. In the easternmost of these pits the bed measures 3 feet 6 inches, but is said to contain much slack'' or dirty lignite. There are probably two beds here, the upper being mined farther west, up the draw. These beds are about 80 feet above river level, and are probably the same as the beds noted near the mouth of Mandan Lake Creek at the same elevation.

In the NE. J sec. 4, T. 143 N., R. 83 W., about half a mile southwest of Mandan Lake, 50 feet above river level, a bed of lignite 2 feet thick was measured. About half a mile south of Mandan Lake, in sec. 3, a bed of hgnite has been mined by stripping. It is about 100 feet above river level. The whole thickness of the bed was not seen, but it is at least 2 feet 6 inches thick.

Wilton District.

For information concerning mines in the Wilton district the writer is indebted to Mr. T. R. Atkinson, state engineer of North Dakota. In 1 907 the Washburn Lignite Coal Company's mine was visited by the writer, but its location and additional data as to the output and equipment have been furnished by Mr. Atkinson.

The exact relation of the deposits mined about Wilton to those near Washburn is not known, but it is believed that they are slightly higher in the geologic section.

Washhum mine. — The Washburn mine, in sec. 1, T. 142 N., R. 80 W., is the largest and most thoroughly equipped mine in the State. Its output for 1907 and 1908 amounted to 109,992 tons. The lignite is reached by a shaft 60 feet deep, which represents the average tliickness of the cover. The underground equipment is very complete and efficient and consists of electric undercutting machinery and electric motors for haulage. The lignite ranges from 8 to 13 feet in thickness, and has a variable parting feet from the bottom. The entries are unusually wide, and timbering is necessary. As a rule, 6 or 8 feet of the bed is taken out first, leaving lignite for a roof, which is taken down when pillars are pulled.

Washbubn Lignite Field, North Dakota. 27

Eckland mine. — In sec. 8, T. 142 N., R. 79 E., is a small opening known as the Eckland mine. The lignite is about 8 feet thick, and has about 45 feet of cover. The annual production is 800 tons.

Lind mine. — In the NE. sec. 6, T. 142 N., R. 79 E., at the Lind mine, the lignite is 11 feet 10 inches thick, under a cover of 35 feet. The production is about 700 tons annually.

Peterson mine, — In sec. 9, T. 142 N., R. 79 E., at the Peterson mine, the bed is 1 1 feet thick, under a cover of 40 feet. The annual production is about 2,000 tons.

Yiengstmine. — At the Yiengst mine, in sec. 34, T. 142 N., R. 79 E., the lignite is 6 feet thick, under 60 feet of cover. The roof and floor are clay. The annual output is about 1,000 tons.

Character And Uses Of The Lignite. General Character.

The lignite of this field is dark browTi in color and tough and woody in structure, but the woody structure is not so evident as in lignite from other parts of the State. It slacks rapidly on exposure to air and sunlight, especially when much handled or subjected to long hauls by rail.

The impurities in the lignite consist mainly of sand and clay partings, which are difliicult of separation in mining. Intimate mixtures of fine sand or clay and lignite, of irregular shape and extent, are rather common in the beds and are not easily detected without close examination, as they have the same color as the lignite.

On weathering, the lignite, which is usually lusterless and massive, breaks into small, shiny cubical blocks, which appear black, but give a brown streak or powder.

Because of the scarcity of timber in this general region lignite is almost the only fuel available for domestic purposes. The state institutions use native lignite exclusively, and to supply this demand, together with a growing demand from manufacturing plants, several well-equipped mines are in operation on main lines of transportation in various parts of the State.

Lignite And Irrigation.

The impracticability of irrigating lowlands along the Missouri by gravity canals has led to the establishment of a pumping plant at Williston, N. Dak., and to the investigation of many other projects for raising water to the desired elevations with lignite as fuel. Two such projects in the Washburn field are now under consideration by the United States Reclamation Service. It is, of course, desirable that lignite be found within easy reach of the proposed location of pumping stations, but this can not always be done, notwithstanding

28 CONtfeftUTtONS TO ECONOMIC GEOLOGY, l9dS, PABT II.

the general distribution of the fuel. However, there are relatively few irrigable flats along the Missouri between Bismarck and the North Dakota-Montana line where lignite can not be found in minable thickness either at hand or within a few miles.

Chemical Analyses And Steaming And Producer-Gas Tests.

The following analyses and tests ° were made at the Geological Surveys fuel-testing plant in St. Louis:

Brown lignite from Wilton mine, Washburn Lignite Coal Company, 1 mile east of Wilton, McLean County, N. Dak., on the Minneapolis, St. Paul and Sault Ste. Marie Railway.

This sample was made up of lump lignite and was shipped under the supervision of M. R. Campbell, of the United States Geological Survey. It was used in making steaming test No. 206 and producer-gas test No. 67.

Mine samples Nos. 1935 and 1938 were taken at widely separated points in the mine

for chemical analysis.

Analyses of samples as received.

Mine samples.

Car sample,

Laboratory 'Laboratory

Air-drying loss

Monture

Volatile matter. Fixed carbon... /Ash

K

£

p4

Hydrogen

Carbon

Oxvgen

Calorific value determined:

Calories

British thermal units. .

7,069

Steaming Test.

Test 206, North Dakota No. 3. — Size as shipped, lump. Size as used, average diameter 3 inches, 76.5 percent; J inch to 1 inch, 10.6 per cent; J inch to J inch, 4.9 per cent; under J inch, 8 per cent. Duration of test, 5.72 hours. Kind of grate, rocking.

Heatine value of coal B. t. u. per pound dry coal. ,

Force of draft:

Under slack damper inch water. ,

Above fire do

Furnace temperature F. ,

Dry coal used per square foot of grate surface per hour pounds. ,

Equivalent water evajwrated per square foot of water-heating surface per hour do

Percentage of nited of boiler developed.

Water apparently evaptmiteti pound of com as flred pounds. .

Water evajwrateil from and at 212 F.:

Per pound of as flrotl do

Per pound of dry i*oal do

Per pound of cofnbiLstible do

Efficiency of Iwilcr, including gmte per cent.

Coal as flred:

Per indiaito*! hour pounds.

Per ele'trlcal hour do

Dry coal:

Per indicateil horseixiwcr hour do

Per elei'trical horseiwwor hour do

Test 206.

11,036

t.lO

o Hull. U. S. (leol. Survey No. AMI, IWV., pp. VM, 1.19.

ft Fon'ed draft.

Washbubn Lignite Field, North Dakota.

Producer-Oas Test.

Test 67 f North Dakota No. S. — Size as shipped, lump. Size as used, over 1 inch, 85 per cent; inch to 1 inch, 6 per cent; J inch to J inch, 3 per cent; under J inch, 6 per cent. Duration of test 50 hours.

Average electrical horsepower 195. 5

Average B. t. u. gas per cubic foot 158. 9

Total coal fired, pounds 30,250

Test 67.

Coal eojMumed in producer {pound per horsepower per hour).

Per electrical horsepower:

Available for outside purposes

Developed at switchboard

Per brake horsepower:

Available tor outside purposes

Developed at engine

Coal as fired.

2. a

EfuivaleiU used fry producer plant (pounds per horsepower per hour).

Per electrical horsepower:

Available tor outside purposes

Developed at switchboard

Per brake horsepower:

Available tor outside purposes '.

Developed at engine

Dry coal.

l.f.9

Combustible.

Briquetting tests of North Dakota lignite have been made by the United States Geological Survey fuel-testing plant and by individuals. No binder is used, but the product is firm and gives excellent results except when subjected to forced draft, which has the effect of disintegrating the briquets and carrying the unbumed particles out through the smokestack.

Another consideration that adds materially to the value of the brown lignite is its surprising success in the producer-gas plant. The following statement has been made concerning the value of North Dakota lignite in the gas producer and gas engine:®

The result of the steam test was so unsatisfactory that there is nothing by which a direct comparison can be made of the efficiency of the fuel used in the producer-gas plant as compared with the efficiency developed in the steam plant. Nevertheless a comparison of the results obtained on other coals under the steam boiler is instructive. The table shows that to produce one electrical horsepower hour in the producergas plant required 2.29 pounds of dry North Dakota lignite, whereas to produce the a&me result in the steam plant required 3.39 pounds of the best West Virginia coal. This means that North Dakota lignite, with the moisture eliminated, will do more work when used in a producer-gas plant than the best coal of the country will do in a steam plant.

a Prof. Paper U. S. Geol. Survey No. 48, pt. 1, 1906, p. 111.

The Fort Berthold Indian Reservation Lignite

Field, North Dakota.

By Caul D. Smith.

Introduction.

The Fort Berthold Indian Reservation, in North Dakota, about 1,500 square miles in area, is divided approximately in half by Missouri River and lies about midway between Bismarck and the point where the Missouri enters the State. In this paper only the part of the reservation north of the river is considered, and as the area lies wholly within the large region of lignite-bearing rocks which covers the western half of North Dakota, it has no natural boundaries. (See fig. 1.)

Heretofore this region has been remote from any railway, but recently a branch of the Minneapolis, St. Paul and Sault Ste. Marie Railway has been extended northwestward from Washburn, crossing the extreme northeast corner of the reservation. The Missouri River Railway, a proposed branch of the Northern Pacific, leaving the main line at Mandan, will follow closely the south bank of the Missouri, if built as surveyed. At certain seasons of the year Missouri River furnishes transportation to and from the field.

The writer was efficiently assisted in the field work on which this paper is based by J. A. Davis, E. B. Hopkins, E. L. De Golyer, and Jay W. Bliss. Mr. De Golyer also assisted in the office work.

The region is essentially a sniootli plain into which the Missouri has cut a valley varying in width from 1 to 2 miles and in depth from 100 to 500 feet. At many points along the river the change from the smooth uplands to the river valley is abrupt and is marked by a narrow strip of bluffs and badlands. At other points, especially where the larger streams enter the river, the gradation is gradual.

Okt Berthold Lignite Field, North Dakota. 31

The field considered here lies within the area once covered by the great continental glacier, whose effect on the topography is everywhere noticeable. In other parts of this general region, beyond the limit of glaciation, where the surface is not protected by the mantle of drift left by the retreating ice sheet, the territory bordering larger streams is in general minutely dissected into a badland belt several miles in width. In the glaciated area the mantle of drift has so tempered erosional action that badlands appear only where degradation has been extremely rapid.

Intermittent lakes occupying depressions that were probably former stream valleys are also features of the region due to glacial action. The valley of Missouri River between the mouth of Little Knife Creek, at the north boundary of the reservation, and the mouth of Shell Creek is comparatively narrow, indicating that it is probably new. It is probable that the river formerly occupied a depression which now lies in a straight line between the mouths of Little Knife and Shell creeks. Another depression southwest of this one, but joining it at the mouth of Shell Creek, may represent a second abandoned valley of the Missouri before it reached its present position.

Geology.

Stratigraphy.

All the stratified rocks in the reservation are of Fort Union (early Eocene) age. Heretofore they have been classed as "Laramie and Fort Union without differentiation, but recent investigations in this general region have proved conclusively that they are Tertiary and they probably correspond to the upper part of the so-called "yellow beds'' in the Sentinel Butte field of North Dakota, the Miles City field of Montana, and the Sheridan field of Wyoming. In this region the beds present a rather monotonous sequence of sombercolored clays and sandy clays interstratified with buff sands and sandstones and beds of lignite. The clays and sandy clays predominate, thus lending to the whole scries a somber hue. The sandstones are usually fine grained and soft, but at many places they contain irregular concretion-like masses of hard sandstone of the same color and texture as the matrix.

The greater part of the field is overlain by a mantle of glacial drift of Wisconsin age. This material is of variable thickness and contains a variety of rocks foreign to the region.

32 Contributions To Economic Geology, 1908, Pabt Ii.

The following detailed section, made at the big bend of Missouri

River 10 miles above the mouth of Shell Creek, gives some idea of the character of the Fort Union formation :

Section at big lend of Missouri River.

Ft. In.

Debris 5

Sand, cream colored 20

Lignite 1 8

Clay 1 3

Lignite 1 8

Clay 5 5

Lignite 3 9

Clay, somber, sandy, contains irriilar masses of hard sandstone, some thin lignite seams, and carbonaceous layers 160

Lignite 4 6

Clay, somber, somewhat sandy 16

Clay, carbonaceous, with lenses of lignite 2

Clay, somber, sandy 5

Clay, yellowish, with sandstone lenses 8

Clay, carbonaceous 1

Sand, clayey 23

Clay, somber, sandy 5 0

Clay, gray 17

Clay, carbonaceous 4

Lignite 6

Clay, carbonaceous 1 6

Lignite 2 10

Clay, gray , 2

Clay 5

Clay, yellowish, sandy 6

Lignite 1

Clay, yellowish 14

Sand, yellowish, clayey, some carbonaceous clay 5 6

Lignite 7 2

Clay, greenish gray with carbonaceous streaks 17

Sand, somber, clayey, contains ferruginous layers 17

Clay, greenish gray 10

Clay, somber, sandy 7

Clay, greenish, white sand at top 6

Sand and clay, somber 18

Lignite 9

Clay, carbonaceous 1

Clay, carbonaceous '2 6

Lii:nito 1 6

Clay, bhiish Ifi

Clay, carbonacfMJus 1

Clav. samiv, somber 10

Clay, carbonaceous 4

Clav. sandv. somber, contains liard sand in places ,'.")

Lignite 1

Fobt Berthold Lignite Field, North Dakota. 33

Ft. In.

Clay, carbonaceoufl 6

Clay, sandy, somber, upper 6 feet contains thin seams of lignite 18

Lignite 1 6

Clay 3

Sand, somber 12

Clay, somber, sandy, contains thin lignite seams 35

Lignite 1 6

Sand, clayey 25

Clay, somber, with thin seams of lignite 40

Lignite 5

Clay 5

Lignite 7

Clay and sand, reddish brown at base 100

Lignite 14-f

Water level in river.

765 11+

The members of this formation are extremely variable horizontally as well as vertically. No particular sandstone or clay bed can be selected as a key rock for purposes of correlation from one part of the field to another. Lignite beds, on account of their greater persistence laterally than the containing rocks, furnish the only meAns of correlation, and they are uncertain where large areas between outcrops are concealed.

Structure.

The strata of the reservation lie almost horizontal. At some places, however, evidence of a slight eastward dip is unmistakable. This was discovered by tracing some of the more persistent lignite beds whose outcrops as followed downstream either approach or dip below river level. The dip is not constant in degree. There are broad areas where the strata lie horizontal, the whole thus constituting a series of gentle unchilations. The amount of the dip at any point is very little more than the fall of the river, and so far as mining operations on a small scale are concerned it may be disregarded.

The Lignite.

General Description.

Lignite beds occur at intervals throughout the rock secticm exposed, Thev arc variable in thickness and horizcmtal extent, but as some of the beds have been traced ccmtinuously for 12 miles by their outcrops they can not justly be described as lenticular. The covering of glacial drift has prevented the tracing or correlation of beds from one part of the field to another. No direct evidence has been obtained as to the thickness of lignite-bearing strata that may

TiH°— Hull, .-si— 10

34 Contributions To Economic Geology, 1908, Part Ii.

underlie the field at a greater depth than river level, but observations made in this same general region lead to the belief that workable beds of lignite can be found to a depth of 1 ,000 feet or more.

On account of the smooth character of the country no exposures of lignite were noted in the uplands away from the breaks of the river, but it is probable that lignite beds occur there and could be found by prospecting.

As lignite is more or less porous and jointed it is a much better medium for the travel of underground water than the fine-grained variable clays and sands which make up the rest of the section. It happens, therefore, that at many places springs and seepages mark the outcrops of lignite beds that are covered by debris.

Wherever exposed in the badlands the thicker bods have been burned along their outcrops, producing a red clinker which consists of baked and partly fused sands and clays. The material immediately underlying a buried-out bed is cmly slightly affected , while the material overlying it may be metamorphosed for a thickness of 20 or 30 feet, depending on the thickness and purity of the bed burned. It is evident, then, that in for a bed of lignite where its outcrop is fringed by clinker, the base of the cHnker, which is usually well marked, will be found on a level with the unbumed body of lignite. The distance back from the outcrop of a bed to which burning may take place depends on the thickness of the cover, but in this comiection it is diflicult to give exact figures. To an observer it is at many places an obvious matter. The persistence of clinker along an outcrop serves to some extent as an index to the character of the bed buried, as thick, pure beds are more apt to bum than thin, impure ones.

The outcrops of the important beds in this field have been traced

and are shown on the map (PI. II). The outline of the whole reser-

vaticm is shown, but little is known of the region south of the river

except that its topography is rougher than on the north

side.

Distribution Of The Lignite.

The lignite beds will described by districts, beginning at the north bouiuhiry of the reservaticm and following in order down the Missouii to the east boundary.

1U(; Bkni) District.

After entering the reservation the Missouri makes a U-shaped bend which terminates near the mouth of Shell Creek. This bend is bordered by high bluffs in which a number of lignite beds ranging in thickness from a few inches to more than 14 feet have been observed. Only four of these beds are of suflicient thickness for mining.

Fobt Bebthold Lignite Field, Nobth Dakota. 35

Bed 1. — The lowest bed, more than 14 feet thick, is exposed in the west bank of Missouri River, opposite and a short distance below Wiedeman's ranch. Water in the river at ordinary stage conceals the base of the bed and at flood time covers it completely. The exposure of the bed is* due to an eastward-pitching anticline of local extent, and it disappears below river level both up and down stream within a few hundred feet of the point where it was measured. The portion of the bed seen is free from partings and appears to be of excellent quality.

Bed 2. — The next bed of consequence exposed in the big-bend district lies about 100 feet stratigraphically above bed 1. Its outcrop has been traced from a point 1 mile below the mouth of Little Knife Creek, at the north boundary of the reservation, to a point 2J miles south of Wicdeman's ranch, and is shown on the map (PI. II). North of Wiedeman's the bed is in one bench, 4 to 5i feet thick, and lies from water level to 30 feet above. It ojtcrop is in the base of the blufi" which forms the east bank of the river and is therefore everywhere near the river. For this reason the bed is almost inaccessible to any means of transportation except by water. Local landslides caused by the undermining action of the river against its bank have broken great masses of lignite from the bed, and these, aftr being washed clean of sand and clay, lie exposed on the bank. Steamboats plying the river frequently stop here for the fuel which can be so easily obtained.

South of Wiedeman's ranch the outcrop of bed 2, which is there made up of two benches, has been traced for about 2 miles. The effect of the local anticline mentioned in connection with bed 1 is felt by bed 2, which for a mile or so rises to an elevation of 50 feet above the river.

Section of bed 2 about '3 miles south of Wicdevians ranch.

Hay Ft. in.

Lignite 4 6

Clay, sandy 4 9

Lignite 3 5

Clay 3

Lignite 3 5

Concealed to river level.

Totallignite 11 4

Near the point where the river turns from a southward to an eastward course bed 2 disappears beneath the hill wash that borders the bottom lands along the river, and was not seen again in the field. Except for a few thin partings bed 2 is comparatively clean, and its quality seems to be good.

36 Contributions To Economic Geology, 1908, Pabt U.

Beds S and 4- — In the badlands bordering the river between Wiedeman's ranch and the mouth of Shell Creek beds 3 and 4 are exposed and then* thicknesses are sufficient to deserve some notice. These beds are 300 and 375 feet, respectively, above river level. They vary considerably but have not been observed to exceed- 4 feet 6 inches in thickness. Immediately south of Wiedeman's they are thin and worthless. They appear to reach their greatest thickness a few miles west of the west line of T. 150 N., R. 92 W. These upper beds are well exposed on the south side of the high bluff, but glacial drift so conceals their northern outcrops that their positions are indefinite. It will be seen from the map (PL II), where their outcrops are shown, that these two beds are outliers, cut off from the region to the north by the low depression which lies between Wiedeman's ranch and Shell Creek.

North of Wiedeman's ranch a part of the outcrop of bed 3 has been traced and is shown on Plate II. The bed has not been observed to exceed 4 feet in thickness and lies near the top of the bluff 300 feet above river level.

South of a small stream which flows westward into the Missouri, about 1 mile south of the north boundary of the reservation, lignite is exposed in several places, and is 2i to 3i feet thick.

Loquemont Creek District.

About 4 miles north of the mouth of Loquomont Creek the Missouri swings against its east bank, forming a bluff in which several beds of lignite are exposed. A section of the bluff follows:

Section 4 niilcs north of month of Loquemont Creek.

D6bri8. Ft. in.

Clay, carbonaceous 4

Sand, clayey 65

Clay, carbonaceous 4

Lignite 5 11

Sand and clay with some thin lignite seams 100

Lignite 1 6

Clay 5 8

Lignite (poor) 3 3

Clay . 5

Lignite 2 10

Concealed to river level 50

247 2

The lower beds of the foretroing secticm are exposed at several places near the wagon road which runs between the bluff and the river. The upper bed appears well up in the bluff, or 170 feet above river level. Its outcrop, shown on Plate II, has been traced for 6 or

Fobt Bebthold Lignite Field, North Dakota. 37

8 miles, and ia places it has been burned. It is 5 to 6 feet thick and seems to be of good quality. Near the mouth of Loquemont Creek it is so concealed that no measurements could be made. The position of the bed makes it easily accessible for mining purposes, and is such that it must underlie a large territory to the east, if it is continuous in that direction.

Elbowoods District.

Between Elbowoods and the mouth of Sixmile Creek the north bank of Missouri River is bordered by a strip of badlands from 1 to 2 miles wide, in which several beds of lignite are exposed. They are nearly everywhere fringed by clinker produced by combustion along their outcrops. Two of them have been mapped, and for convenience of reference are designated as beds 1 and 2.

Section 5 miles east of Elbowoods.

Ft. In.

Sand, somber, clayey 50

Lignite 3

Clay, sandy 8

Lignite 4

Clay, somber 34

Lignite (bed 2) 6 6

Clay, somber 20

Lignite 1

Clay, somber 9

Lignite 2

Sand and clay, some carbonaceous layers 35

Sand with irregular hard lenses 45

Lignite (bed 1) 7

Clay, somber, sandy 22

Lignite 1 9

Clay, gray 1 4

Lignite 2 7

Clay, somber, sandy 14 5

Concealed to river level, about 60

326 7

Bed 1. — At a point about 4 miles east of Elbowoods, where Missouri River swings to the north against the badland bhiffs, bed 1. the lowest considered in the section, is about 70 feet above water level, or 50 feet above the flood plain of the river. To the southeast it outcrops in the base of the bluff everywhere near the edge of the river flat, and dips gradually eastward to the western part of T. 147 N., R 88 W., where it disappcai-s below the alluvium. The beil is nearly overvwhere fringed hv clinker and for that reason is easily traceable. Near Elbowoods bed 1 is badly split up by part-

38 Contributions To Economic Geology, 1908, Part Ii.

ings, but they appear to die out to the southeast. Some sections of the bed follow:

Section of bed J in S. J sec. 31, T. US N., R. 89 W.

Ft. In.

Lignite 9

Parting 9

Lignite 1

Parting 6

Lignite 2 6

Total lignite 4 3

Section of bed 1 in NE. sec. 6, T, 147 N., R. 89 W,

Ft. In.

Lignite 2 6

Parting 4

Lignite 2

Parting 2

Lignite 2

Total lignite 6 6

In the N. i sec. 24, T. 147 N., R. SO W., bed 1 is about 7 feet thick and free from partings.

Bed 2. — About 125 feet above bed 1, or 200 feet above river leVel, is another bed which has been traced from a point near Elbowoods eastward to the boundary of the reservation. It has been burned almost continuously along its outcrop, and its thickness was measured in only two places, where it was 4 feet and 6 feet 6 inches thick. To judge by the thickness and persistence of clinker produced by its burning, it is probably a workable bed throughout the distance traced.

Between Missouri River and Sixmile Creek bed 2 lies in a narrow strip with disconnected outliers. PVom Sixmile Creek eastward to the boundary of the reservation bed 2 is about 125 feet above river level and outcrops at the north edge of the lowland bench, 2 to 4 miles from the Missouri.

In the hills north of Elbowoods no lignite is exposed, but springs and seepages, probably indicating the outcrops of beds, are abundant, especially near the north edge of the lowlands on which the town of Elbowoods is situated.

In the eastern part of T. 148 N., R. 91 W., northwest of Elbowoods, several thin beds of lignite are exposed, but none of them has been observed to exceed 3 feet 8 inches in thiclviiess.

Character And Uses Of The Lignite.

The lignite on the reservation docs not difTer in character and composition from that in other parts of the same general region. It is dark brown in color, tough, and woody in structure. The greatest disadvantage encountered in dealing with a lignite is its

Fort Berthold Lignite Field, North Dakota. 39

to the atmosphere. Attempts have been made to overcome this difficulty by briquetting the fuel, but the scheme has not yet come into practical use. When, however, the lignite is not handled much and is kept under shelter away from the action of sunlight and rain it has been known to hold together in good condition through the winter months.

The impurities in the lignite consist mainly of sand and clay partings which are difficult of separation in mining. Intimate mixtures of fine sand or clay and lignite, of irregular shape and extent, are rather common in the beds, and are not easily detected without close examination, as they have the same color as the lignite.

On weathering the lignite, which is usually lusterless and massive, breaks into small, shiny cubical blocks which appear black but give a brown streak or powder.

In the absence of timber lignite is used generally over the region for domestic purposes and is coming into favor as a fuel for various manufacturing industries throughout the vState. As most of the inhabitants of the Fort Berthold Reservation live near Missouri River, where timber is plentiful, very little lignite is mined, and that only where conditions are extremely favorable — for example, in places where it can be taken from open pits and it is necessary to remove very little cover to reach the fuel. Timber suitable for mining purposes can be obtained only in the valley of Missouri River.

Future Development.

Owing to the wide distribution of lignite in this general region it is not likely that any part of the area develop far in advance of any other part. Some small advantage would arise, of course, should a certain field have extremely favorable conditions as to transportation and thickness and purity of fuel. It seems probable, however, that the lignite will have only a local use for many years to come.

Probably the greatest future use of the lignite will be to generate power for pumping plants to irrigate lands along the larger streams in the State. A number of such projects on Missouri Kiver are now under consideration by the United States Reclamation Service and by the State. One such plant has already been established at Williston. Should these numerous projects be completed great quantities of lignite would be necessary not only for their use, but also to supply settlers attracted by irrigated lands with fuel for domestic purposes, and to supply industries that would probably spring up with an influx of immigration.

North Dakota brown lignite has been tested with groat success in the producer-gas plant, as shown by the statement (quoted on pages 28-29.

The Fort Peck Indian Reservation Lignite Field,

Montana.

By Carl D. Smith.

Introduction.

The Fort Peck Indian Reservation lignite field lies in the northeast comer of Montana, partly in Valley County and partly in Dawson County. (See fig. 1.) Missouri River flows eastward through the field and forms the south boundary of the reservation. The Great Northern Railway follows the valley of the Missouri across the field. At certain seasons of the year the river is navigable, but it is rarely used as a means of transportation.

The investigation on which tliis paper is based was made in 1908. In the smveyed parts of the field locations were obtained by means of horseback traverses, with frequent ties to established land corners. Where the land has not been surveyed, the main control lines were run by plane-table and buggy-wheel traverses, which were tied to established corners wherever possible and were supplemented by horseback traverses. At the time geologic examinations of the field were being made topographic surveys were in progress on a part of the reservation, but these were not available in the field.

This paper is intended to be entirely of an economic nature, hence little attention is given to matters that do not immediately concern the lignite. As a result of the work of 1908 the mapped area of formations barren of lignite has been extended eastward along Missouri River for a distance of 60 miles.

The writer is deeply indebted to Messrs. J. A. Davis, E. B. Hopkins, and E. L. De Golyer, whose interest and able assistance in the field work have contributed greatly to whatever value this report may have. Mr. De Golyer also rendered able assistance in the office.

Topography.

The valley of Missouri Kiver divides the field into two distinct topographic provinces. North of the river for a distance of 15 to 20 miles the slopes are as a rule gentle and, with a few exceptions, the valleys are broad with gently sloping sides. Farther north the relief becomes bolder and the large streams are in places bordered

Port Peck Lignite Field, Montana.

by abrupt escarpments and hills ranging in elevation from 200 to 500 feet. The interstream areas are usually broad and flat.

In the north-central part of the reservation, south of Poplar River and Cottonwood Creek, is a gravel-covered terrace about 300 feet above stream level, which slopes gently to the southeast. A remnant of a similar terrace appears in the highlands north of Cottonwood Creek.

South of Missouri River bluffs and hills rise abruptly from the edge of the flood plain to an elevation of several hundred feet. Near the river the topography is rough and in places the country is dissected into badlands, but farther to the south the badlands blend with rolling prairies of low relief.

The entire field considered here lies within the area once covered by the great continental ice sheet, whose effects on the topography are everywiiero evident. Preglacial streams have been caused to abandon their channels, which now appear either as broad depressions containing intermittent lakes or as broad valleys occupied by streams of insignificant size. The movement of the glacier over the region has no doubt had a tendency to smooth away preexisting inequalities of the surface, and the retreating ice sheet has left a mantle of drift which has protected underlying formations from the erosion into badland forms common in regions not so protected. South of Missouri River evidences of glaciation are not so marked as they are

north of the river.

Geology.

Stratigraphy.

The following table gives a suimnary of the formations occurring in this field :

Stratigraphy of the Fort Peck Indian Reservation lignite field, Montana.

System.

Quaternary Twtlary

Otacpou8(?)

Formation.

Thick-

Feet.

Fort Union formation l,00()-f

Fox II ills C?) sanlstonr 200

I'lirre shalo 1 ,

l)(\scription.

Alluvium.

Glaiiahlhft.

Yellowish sands and .sandstones inforboddod

with grav clays and liRnitn. Somber-colorrtl sands and clays with nu-

inerou."' layers and a few lig-

HufT-oolorcd soft sandstones

with some pray clay. Dark-jrray shale, in phiecs lirown. Very soft

uml frl-ible.

Pieuuk Siialk.

The basal member of the rock section occurrinjj in the Fort Pock field is a dark-gray shalo, in places brown, which is as a whole very soft and friable, but contains at irregular intervals thin layers of

42 CONTRIBUTIONS tO ECONOMIC GEOLOGY, 1908, PART II.

limy material. Near the top of the formation appear many bowlderlike limy concretions, 1 to 2 feet in diameter, some of which are made up almost wholly of fossil shells. Others contain no fossils and many are intersected by a network of calcite veins which are usually of a lighter color than the matrix.

According to T. W. Stanton fossils collected from this formation are very distinctive. ''In fact, they are characteristic of a horizon in the upper Pierre corresponding to the shale above the Judith River formation which farther west in Montana has been called the Bearpaw shale."

As indicated on the accompanying map (PI. Ill) the Pierre shale covers the greater part of the west end of the field and extends eastward in an area of varying width along Missouri River nearly to the town of Brockton, on the Great Northern Railway. The base of the shale does not appear in the Fort Peck field, but there is reason to believe that it is more than 1 ,000 feet thick, as at least that thickness occurs in this field. The Pierre shale is barren of coal, and so far as known carries no other economic product, with the possible exception of clay for brickmaking. As the shale contains no ledge-making material bluffs are rare in the area which it underlies as the surface rock. Streams whose courses lie in the shale are usuallv more alkaline than those elsewhere.

Fox Hills (?) Sandstone.

Conformably overlying the Pierre shale is a series about 200 feet thick consisting of buff sandstones interstratified with some gray clay. As a rule the sandstone is soft, but in places it appears as hard concretion-like masses which stand out as ledges in the process of weathering or as masses of cannon-ball shape embedded in a matrix of softer rock. The material shows great irregularity of bedding, is extremely variable in character horizontally, and is in places cross-bedded and conglomeratic.

The age of these beds is doubtful. They occupy a position in the section which to the south and southeast is occupied by the Fox Hills sandstone, but no fossils could be found in the beds; hence further work in the region will be necessary to determine their age. For the present they are called Fox Hills (?) sandstone. Like the Pierre shale these buff beds are barren of coal. Excellent exposures of this formation can be seen in the part of the field south of Missouri River, especially in the high river bluff south of Brockton. North of the river glacial drift so conceals the formation that good exposures can be scon at only a few places. These are near the head of Cottonwood Creek in the northern ])art of the reservaticm, and on Wolf Creek near the town of Vvolf Point.

Fort Peck Lignite Field, Montana. 43

Somber-Colored Beds.

About 200 feet of somber-colored sands and clays, with numerous carbonaceous layers and a few beds of impure lignite, overlie the Fox Hills (?) sandstone and are also of doubtful age. They are regarded by F. H. Knowlton as having very strong Fort Union (early Eocene) affinities. In the field covered by this report there is no apparent unconformity between the Fox Hills (?) sandstone and the sombercolored beds. Although the upper part of the somber-colored beds differs from the lower part of the Fox Hills (?) sandstone in character of constituent materials the two formations so grade into each other that their contact is very indefinite. At some places the somber-colored beds contain irregular masses of hard sandstone and thin beds of impure limestone. In weathering this hard material stands out as ledges or serves as protecting caps for pedestals of softer sands or clays. Excellent exposures of the somber-colored beds can be seen in the badlands south of Missouri River, on Cottonwood Creek, and Poplar River in the Fort Peck Indian Reservation. Because of the uncertainty of the position of the contact of the Fox Hills (?) sandstone and the somber-colored beds north of Missouri River they have been grouped together in mapping.

Fort Union Formation.

The uppermost formation in the Fort Peck region is made up of yellowish sands and sandstones interbedded with gray clays and lignite, the sands and sandstones predominating. One thousand feet or more of this formation, which appears to represent more stable conditions of deposition than the Fox Hills (?) sandstone and the somber-colored beds below, is exposed in the field. As a whole this formation has a yellowish hue. According to F. II. Knowlton the beds are Fort Union in age. Their contact with the somber-colored beds below is usually well marked by an abrupt change in color and character of material. Lignite occurs abundantly in these yellow beds, and is much more constant in quality and horizontal distribution than the lignite of the somber-colored beds. Excellent exposures of the yellow Fort Union formation can be seen east of Brockton both north and south of the river, in the northeastern part of the reservation, and in the escarpments bordering the valley of Poplar River.

Glacial Drift.

Overlying the greater part of the field is a mantle of glacial material of varying thickness, made up principally of igneous bowlders and clay, but containing some fossiliferous limestones. These bowlders vary in size from mere pebbles to masses weighing probably 20 tons. It is probable that this drift formerly covered the entire region like a

44 Contributions To Economic Geology, 1908, Part Ii.

huge blanket, but stream action and weathering agencies subsequent to the retreat of the continental ice sheet have cut deep channels through the drift and into underlying formations. It may be readily seen that isolated exposures of the underlying rock not concealed by glacial drift are rather diflScult of correlation, and this diflSculty is augmented by the variability of the lignite-bearing formations.

Structure.

As originally deposited the strata which make up the rock section in and near the Fort Peck Indian Reservation were approximately horizontal, but since their deposition some force has so tilted them that they now dip gently toward the east. This dip, however, is not constant in direction nor degree. A low dome, near the center of which Poplar is located, breaks the continuity of the dip, and causes a slight reverse dip to the west, thus producing a shallow syncline pitching southeastward whose axis trends northwest and southeast a few miles east of Wolf Point. The formations immediately concerned in the Poplar dome dip away from it in every direction, the direction of the dip at any particular point being determined by the direction of such a point of observation from the center of the dome. Thus the formations at a point due east of the center dip to the east. The lignite beds along the river east of Brockton dip eastward at about 100 to 135 feet to tlie mile. In directions other than east of the dome, whore its presence only intensifies the general dip, its effect does not reach beyond 15 miles.

The Lignite.

General Description.

By reference to the sections given on the following pages it will be noted that many lignite beds occur in this field. Relatively few of these beds, however, are of sufficient thickness for consideration as mining Wherever wide areas are concealed between the districts discussed no attempt has been made to correlate individual beds from one to another.

The character of the materials that inclose lignite beds is so changeable that it is never to what the roof and floor of any particuhir IhmI are likely to bo a few yards from the ])oint of actual exposure. As a general rule it may he said that a few feet of the lignite bed itself, should its thickness permit, will make a much stronger roof than anv material that may overlie it. Timber suitable for mine pur])()ses is very scarce except in the valley of Missouri Water, while not abundant except in the rivers, could be stored by building reservoirs in small streams and could possibly be obtained from wells.

The beds which occur in the somluM-colored formation have shown so nuich variability in (juality, thickness, and lateral

Fort Peck Lignite Field, Montana. 45

extent that, in the presence of better lignite in the Fort Union formation, they are considered worthless as a whole. In places they have a workable thickness and have been burned along their outcrops, but on account of their uncertainty of character no attempt was made to note them closely.

Lignite beds of workable thickness and purity occur at intervals through the entire thickness of the Fort Union formation exposed in the field. They are much more constant in character than those occurring in the somber-colored beds, and are here treated more in detail. Near Missouri River the outcrops of the principal beds have been traced and mapped, but away from the river no attempt has been made to follow out individual beds.

A feature of the region, especially noticeable south of Missouri River, is the clinker produced by the burning of lignite beds along their outcrops. This material, which is usually red, is an unfailing index to the position of the bed burned. It would, in many localities, be extremely difficult to meander outcrops of beds without the clinker as a guide. To some extent also the persistence and thickness of the clinker give some idea of the persistence, quality, and thickness of the burnt bed, as thick beds of good quality produce a greater thickness and more completely fused zones of clinker than thin or impure beds. The distance back from the outcrop of a bed to which burning may take place is governed by the thickness of cover, which, if great enough, smothers the fire by preventing access of air. In this connection it is impossible to giv§ exact figures, as no mining or prospecting has been done where it was necessary to remove the clinker to reach the lignite. To the observer, however, the width of the clinkered zone is often an obvious matter. In prospecting for lignite on an outcrop that has been burned it may be well to keep in mind the fact that the base of the clinker, which is usually well marked, is on a level with the base of the burnt bed of lignite.

The areal distribution of the formations that occur in this field is shown on Plate III. The principal wagon roads are shown, except those in the valley of Missouri River, where there is such a network of roads that to represent them would only complicate the map.

The outcrops of important beds of lignite in the eastern })art of the field are also shown on the map. In the field no attempt was made to map the contact of the river alluvium with older formations. The map is compiled from Missouri River Commission maps and township plats of the General Land Office. The Fort Peck Indian Reservation constitutes the greater part of the field. The north boundary of the reservation is the north boundary of the area mapped. On the west the reservation is bounded by Porcupine Creek, on the south by Missouri River, and on the east by Big Muddy Creek.

46 CONTRIBUTIONS TO ECONOMIC GEOLOGY, PABT n.

Distribution Of Lignite.

For convenience of description the field is divided into more or less arbitrary districts. The districts nearest the Great Northern Railway and Missouri River, on account of their accessibility, have been examined in greater detail than those more remote from lines of transportation.

Brockton-Culbertson District.

The Brockton-Culbertson district includes the region in the reservation east of Brockton, between Missouri River and the seventh standard parallel, and a small area about Culbertson east of Big Muddy Creek. This district, because of its accessibility, has been studied in more detail than other parts of the field, especially in T. 28 N., Rs. 53 and 54 E., where the two important lignite beds have been followed in their outcrops by means of stadia measurements and where concealed have been prospected by means of a hand drill.

The dip of the lignite beds and containing formations in this district is to the east, its amount ranging from 25 to 135 feet to the mile. A section compiled from scattered exposures and supplemented by observations made south of Missouri River, with unimportant lignite beds eliminated, is given below. For convenience of description, the important beds are designated by letters A, B, C, etc., A corresponding to the lowest workable bed.

Section in Brockton-Culbertson district.

Ft. In.

Lignite (bed G) 9

Clay and sand 90

Lignite 4-6

Clay 10-27

Lignite (bed F) 5 6

Sand and clay 70

Lignite (bed E) 3-6

Sand and clay 130

Lignite 5 7

Clay 6

Lignite (bed D) 9

Sand and clay 95

Lignite (bed C) 2

Sand and clay 115

Lignite (bed B)..* 1-5 6

Sand and clay 275

Lignite 5

Clay 15

Lignite (bed A) 7 7

884 2

Fort Peck Lignite Field, Montana. 47

From the above section it may be noted that about 900 feet of strata bearing workable beds of lignite are exposed in the Brockton- Culbertson district.

Only three beds of lignite occurring in this district east of Big Muddy Creek are of suflScient thickness to warrant consideration. On the map these are termed beds F and G, F being made to include the two lower beds, which are so close together in the section that their mapped outcrops practically coincide. The outcrops of these beds are shown on the map (PI. III). The prevailing eastward dip of the beds is so much less about Culbertson as to be practically negligible so far as its effects on mining is concerned.

Bed In T. 28 N., R. 53 E., bed A lies at the contact of the somber-colored beds with the Fort Union formation above. Another bed appears a few feet above bed A, and it is possible that in attempting to map the outcrop of bed A locations were at some places taken on the upper bed, but they are so near in the geologic section that their outcrops practically coincide.

The outcrop of bed A is shown on Plate III. From the point where Box Elder Creek flows out of the hills into river alluvium the bed rises gradually northwestward to the top of the divide between the river and Lake Creek. From the top of the divide the outcrop of the bed was followed in a northeast course to the seventh standard parallel. The bed dips to the east about 100 feet to the mile and presumably underlies all the territory east of its mapped outcrop. In sees. 21 and 22 bed A has been burned along its outcrop, producing a considerable amount of red clinker. A section of bed A in the NE. i sec. 21, T. 28 N., R. 53 E., shows 6 feet 5 inches of lignite, with sandstone roof and clay floor.

Near the middle of sec. 21, T. 28 N., R. 53 E., bed A is exposed naturally in the point of a hill, where the following section was measured :

Section of bed A near middle of sec. 21 y T. 28 N., R. 53 E.

Clay roof. Ft. in.

Lignite 2 2

Clay 1

Lignite 2 7

Lignite, dirty 4

Lignite 2 G

Total lignite 7 7

A hole drilled in the NE. sec. 8 revealed only 4 feet 8 inches of lignite. It is probable that the lignite struck here is the smaller upper bed which lies about 10 feet above bed A.

48 Contributions To Economic Geology, 1908, Part H.

An exposure of the small bed above bed A was seen in the SE. i sec. 22 near the wagon road, just east of Box Elder Creek. A section follows:

Section ofligniU bed in SE. J sec. 22, T. 28 JV., R. 53 E.

Sandy clay roof. Ft. In.

Lignite 1 6

Clay 1

Lignite 3 6

Total lignite 5

Several attempts were made to reach bed A at points along its outcrop, but it is so concealed by glacial drift that no satisfactory results could be obtained. Bed A wherever measured contains some thin partings, but they are not of sufficient thickness to interfere seriously with mining operations. No attempt was made to follow the outcrop of this bed north of the seventh standard parallel.

Accessible parts of' the outcrop of bed A are probably too far from the river to utilize that stream as a source of .water for mining purposes, but a reservoir could be formed by damming Box Elder Creek. In case no great amount of water should be needed, it might be obtained from wells, possibly artesian.

Bed B,—ln sees. 30 and 31, T. 28 N., R. 54 E., just north of the Great Northern Railway, is a small area of badlands in which bed B is well exposed. It is 300 feet higher in the rock section than bed A, and, like the beds above and below it, rises gradually to the west. Many exposures of the bed were measured, but it shows so much variability in thickness that it is not considered of much value. Its greatest measured thickness is 5 feet 6 inches and its least 1 foot. It is usually very impure.

Bed C. — In the Brockton-Culbertson district bed C is about 2 feet thick and is of little consecjiuence. It is included here principally because it is thicker on the south side of the river. It is about 115 feet above bed B in the rock section, and was measured in only one place, in the western part of T. 28 N., R. 54 p].

Bed I). — For about 500 feet in the section above bed A many thin beds of lignite occur, but none of them has shown workable thickness in the Brockton-Culbertson district. The outcrop of bed D is similar to that of bed A in that it swings to the northwest from the edge of the river alluvium to the top of the divide between the river and Lake Creek, thence northeastward to the seventh standard parallel, which its outcrop was not followed. The outcrop lies almost wholly in T. 28 N., U. 54 E., and the dip of the bed to the east in the western part of the township is about 135 feet to the mile. somewhat more than the dip of bed A. It presumably underlies all the territory cast of its outcrop.

Fort Peck Lignite Field, Montana. 49

East of the point where the outcrop of bed D is concealed by river alluvium there is probably a diminution in the amount of dip. In other words, from sec. 26 eastward to Big Muddy Creek bed D probably lies almost flat, but is still inclined slightly to the east.

Westward from the middle of sec. 20 bed D has been burned for a short distance along its outcrop. Near the middle of sec. 20 a hole was drilled which revealed the following section:

Section of lignite in drill hole in sec. 20, T.i8N.,R. 54 E.

Clay roof. Ft. in.

Lignite 5 7

Clay , sandy 6

Lignite (bed D) 9

Total lignite 14 7

Another hole was drilled through bed D near the middle of sec. 4, and revealed 8 feet 8 inches of lignite.

A bed of lignite 5 feet 7 inches thick overlies bed D, from which it 18 separated by 6 feet of clay. These beds are so near that the general conditions affecting one also apply to the other.

Bed E, — No exposure of bed E was seen in the Brockton-Culbertson district. The thickness given in the general section was measured on the south side of Missouri River, where the bed is well exposed and lies about 140 feet stratigraphically above bed D.

Bed F. — It will be seen by reference to the map (PI. Ill) that bed F underlies considerable territory in T. 28 N., Rs. 55 and 56 E. Its outcrop follows closely the base of the hills bordering the flood plains of Big Muddy Creek and Missouri River, and in elevation it is about 100 feet above the Missouri. Above bed F and separated from it by 10 to 27 feet is another bed which in places reaches workable thickness.

Section of bed F near quarter comer between sees. 5 and 6, T. 28 N. R. 55 E.

Foet.

Lignite G

Clay and sand 27

Lignite (bed F) 4-f

Total lignite 10-f

In this section the base of bed F is concealed. Two exposures about li miles farther northwest showed 6 to 8 feet of lignite, free from partings.

Section of bed F in SW. sec. 26, T. 28 AT., R. 55 E.

Ft. In.

Lignite 3 8

Clay and sand 17

Lignite (bed F) 5

Totallignite 8 8

7963*— Bull. 381—10 4

60 Contributions To Economic Geology, 1908, Part Ii.

Where the bed is not covered by hill wash it is in many places so fringed by clinker that no satisfactory measurements could be made. Both benches of bed F are free from partings and appear to be of excellent quality.

Bed G.-A patt of the outcrop of bed G, 115 feet above bed F or 215 feet above Missouri River level, has been mapped near Culbertson. The thickness of the bed was measured in only one place, at the Bruegger mine, 3 miles north of Culbertson, a description of which follows. This bed has been burned somewhat along its outcrop. Its exploitation is considered a safe mining venture, but it is rather inaccessible on account of its elevation and distance from means of transportation.

About 3 miles north of Culbertson the Bruegger mine has been opened on bed G. The main entry runs north and is about 200 feet in length. The bed is 8 feet 6 inches to 9 feet thick, is free from partings, and is of good quality, as shown by the analysis on page 65. The fuel is hauled by wagons to Culbertson for local use.

District South Of Missouri River.

The district described here is bounded on the north by Missouri River, on the west by the tenth guide meridian, and on the south by the sixth standard parallel, and extends eastward to a point south of Missouri River opposite Culbertson.

In structure it is similar to the region north of the river. The general dip is to the east or a little south of east, with a slight reverse dip to the west from Redwater River westward for 15 miles. This reverse dip is due to the shallow, southeastward-pitching syncline mentioned above as lying between the Poplar dome and Wolf Point. The effect of this syncline is to bring the lower contact of the Fort Union the principal lignittbearing formation, to a lower level and therefore nearer the river. Westward from the mouth of Swartz Creek, Wolf Point, the IhhIs rise gradually, thus the Fort Union lignite-bearing formation farther from Missouri River.

The contact of the soniber-<*oloreii IhhIs with the overlying Fort Union formation, at or above which the better IhhIs of liirnite occur, is shown on the map (PI. III>. The lignite which ixxurs near this horizon, west of Charlie Creek, because of its general inaccessibility in that direction, has not IxHn measureil or mapfXHl with as much ccunicy as the beils east of Charlie Oeek. Workable bods near the river west of Charlie C nnk ixxnir as irngular outliers with thin coTer, 400 feet or mon the river Ixttoms. In the southern part of T. 27 X.. R. 49 E.. a 5-fiXt beil of lignite ixxnirs in the sombercolorpd beds and it has been mineil to some extent on Xickwall Cieek for use at Poplar.

Fort Peck Lignite Field, Montana. 51

The eastward dip whose effect begs to be felt strongly 10 miles east of Redwater River brings the base of the Fort Union, the principal lignite-bearing formation, down to river level near the mouth of Chariie Creek, eastward from which hgnite beds successively higher in the section appear near river level.

East of the mouth of Charlie Creek lignite beds occur in abundance and have practically the same distribution stratigraphically as in the Brockton-Culbertson district. For convenience of description the important beds are designated by letters, similar letters being given to beds correlated as the same in the two districts.

Bed A, — The bed of lignite which occurs at the contact of the Fort Union formation and the somber-colored beds in the Brockton- Culbertson district appears south of the river in T. 27 N., R. 53 E., near Charlie Creek. The bed dips to the east about 100 feet to the mile and disappears below the level of Missouri River a short distance east of the mouth of Charlie Creek. Near the river the outcrop of bed A is so concealed that only a partial exposure could be seen. This was near West CharUe Creek, in the southern part of T. 27 N., R. 53 E. A section follows:

Section of bed A on West Charlie Creek.

Sand roof. Ft. In.

Lignite 2

Parting 2

Lignite 1 6

Parting 1

Lignite 1 5

Parting 1

Lignite 2 9

Parting 2

Lignite (base concealed) 7

Total lignite exposed 6 5

East of the mouth of Charlie Creek the outcrop of bed A should be found near the river, but its character and thickness there are not known.

Bed B. — South of Missouri River bed B could not be recognized. Its outcrop should lie between the mouth of Charlie Creek and Balls Bluff to the east, but from its character north of the river it is not surprising that the bed should have pinched out here.

East of the mouth of Charlie Creek the outcrops of the principal lignite beds have been followed only near the river, where they are well exposed in the bluffs and badlands.

Bed C, — In Balls Bluff, just south of Missouri River in the northcentral part of T. 27 N., R. 54 E., bed C is well exposed and averages 4 to 6 feet in thickness. Here the bed is about 150 feet above the river, but near the east line of the township the eastward dip of th

52 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1W8, PABT n.

bed carries it below river level. Westward from Balls Bluff the outcrop of bed C rises rapidly and swings to the south, where it could not be followed because of the smooth, grass-covered character of the country.

Bed D, — In outcrop bed D closely follows bed C, from which it is separated by 50 to 100 feet of sandy clay, but on account of the diminution of the dip to the east it extends down Missouri River nearly to the mouth of Twomile Creek before disappearing. Bed D averages nearly 10 feet in thickness and has in places a few partings that arc too thin to interfere with mining. Some detailed measurements of bed D follow:

Section of bed D in eastern part of T. 27 JV., R. 54 E.

Sandy clay roof. Ft. in.

Lignite 6 6

Clay 3

Lignite 2 10

Sand 2

Lignite 6

Total lignite 9 10

Section of bed D at Balls Bluff in north-central part of T. 27 N., R. 54 E,

Soft sandstone roof. Ft. In.

Lignite, dirty 1

Lignite 6 6

Clay 2

Lignite 2 6

Total lignite 10

At a number of points along their outcrops beds C and D are well located with reference to transportation by water, and are easily accessible to mining for domestic purposes.

Beds E, and (r.— In T. 27 N., R. 54 E., and between Twomile and Ilardscrabble creeks, beds E and F appear as narrow outliers capping the highest divides. Their outcrops are nearly everywhere fringed by clinker, making frequent measurements of their thickness impossible by the usual means. Near the east line of T. 27 N., R. 54 E., the eastward dip of the beds is about 100 feet to the mile, but farther east the dip diminishes considerably, probably not amounting to more than 25 feet to the mile opposite Culbertson.

A section of bed E in the northeast-central part of T. 27 N., R.

54 E., shows 8 feet 8 inches of good lignite. To the east the bed diminishes considerably in thickness. In the SW. sec. 11, T. 27 N., R.

55 E., it is about. 4 feet thick, with a thin parting near the base. A measurement of bod E in the N. i sec. 8, T. 27 N., R. 56 E., in the south bank of Missouri River opposite Culbertson, shows 4 feet 9 inches of lignite, with three thin partings. East of Hardscrabble

Fort Peck Lignite Field, Montaka. 53

Creek bed F occurs near the top of the bluff bordering the river flat and is burnt continuously along its outcrop. The bed lies about 150 feet above river level near the mouth of Hardscrabble Creek and 100 feet above river level at the ferry south of Culbertson. The dip of the bed to the east is probably not more than 25 feet to the mile, hence so far as mining is concerned it may be regarded as lying flat.

About half a mile west of the ferry south of Culbertson, where the wagon road crosses the point of a hill, 8 feet 6 inches of bed F was measured, the base being concealed. It is here free from partings and appears to be of excellent quality.

Section of bed Fin NW, J sec, 9, T. rt N,, R, 66 E.

Sandstone roof. Ft. In.

Lignite 4

Clay and sandy clay 16

Lignite (bed F) 6 6

Total lignite 10 6

One-fourth mile east of this locality a mine has been opened on bed F. A section follows :

Section of bed F in sec, 9, T. 27 N., R. 66 E.

Clay roof. Ft. in.

Lignite 3 11

Clay 2

Lignite 3 9

Clay 1

Lignite 1 10

Total lignite H 6

The great thickness of clinker attending bed F is probably due to the combustion of this bed together with the 4-foot bed 15 to 20 feet above.

Bed F, though not ideally situated with reference to water transportation, is at many places near enough to the river to be reached by an incline from the edge of the water. The quality of the bed is everywhere apparently good.

The outcrop of bed G was not traced south of Missouri River. About 2 miles south of Culbertson ferry this bed is exposed and measures 5 feet 6 inches of clean lignite.

Northeast Corner Of Reservation.

No attempt has been made to trace individual beds of lignite in the northeast corner of the reservation, as the region is so covered by glacial material as to make close correlations impossible. As in other parts of the field the contact of the somber-colored beds with

54 Contributions To Economic Geoloqt, 1908 Past Il

the Fort Union formation above marks practically the lower limit of workable lignite. Above this contact the distribution of lignite beds is probably not radically different from their distribution in the Brockton-Culbertson district, except that beds higher in the stratigraphic section appear. The general dip of the strata is to the east, possibly a little south of east; in amount ranging from a few feet to 100 feet to the mile.

Lignite on Smoke CreeJc. — Lignite is exposed at many places on Smoke Creek near water level. In all probability these exposures are on the same bed, whose dip to the southeast is practically the same as the fall of the creek. At no place could the full thickness be seen. Near West's ranch the bed has been mined for local use. Some sections follow :

Section about 4 miles up Smoke Creek from Wests ranch.

Ft. Id.

Lignite 2 6

Parting 1

Lignite (base concealed) 4 2

Section in north hank of Smoke Creek at Wesls ranch.

Ft. In.

Lignite 2 5 .

Parting 1

Lignite (base concealed) 4 2

Sectimi about 6i miles down Sinoke Creek WesVs ranch.

Ft. In.

Lignite 2 6

Parting 1

Lignite (base concealer!) 5 6

In the bluff south of West's ranch a number of lignite beds appear, two of which have been buried along their outcrops and may be of workable thickness. These are 140 and 160 feet above the level of Smoke Creek.

Lignite on Sauerkraut Creek, — A bed of lignite 5 feet 10 inches thick is exposed on Sauerkraut Creek, a small stream that flows southeastward Smoke and Wolf creeks. About miles southwest of Scott's ranch on Wolf Creek the lignite has been mined for local use. The bed appears to dip slightly to the southeast and is overlain by sandstone. Other exposures of thin beds of lignite were noted on Sauerkraut Creek.

Lignite near Wolf (Wck. — Near the heads of small streams which enter Wolf Creek from the west the country is cut into badlands, exposing several beds of lignite. Those beds have been considerably burned in their outcrops, forming a red clinkcM'. A measurement of the thickest bed gave 6 feet of lignite, with a 4-inch parting 1 foot from the top.

Outcrop of lignite

T.ignite

Lignite exposure or dcilLliole

pc

Fobt Peck Lignite Field, Montana. $5

A section of the rocks exposed at the head of a small stream entering Wolf Creek from the west 6 miles upstream from Scott's ranch follows :

Section of beds west of Wolf Creek.

Ft. in.

Sands imd clays, yellowish 150

Sand, blue and yellow 20

Clay, carbonaceous 6

Sandstone, yellow 12

Clay, some lignite 9

Sand and clay 15

Clay, carbonaceous 2

Clay, sandy 21

Sand 10

Lignite 8

Clay 10

Clay, sandy 17

Lignite 8

Clay 4

Lignite 1

Clay 8

Sand, yellow 16

Clay and sand 15

Lignite 3

Sand 6

Lignite 6

Clay and sand 15

Lignite 2

Sand and clay 60

Level of Wolf Creek.

401 1

Very little lignite shows in the drainage basin of Wolf Creek, except as noted in the foregoing section, about 75 feet above the level of the stream, although a section of rocks 500 feet or more thick is well exposed in the region.

On the east side of Wolf Creek, 15 miles above Scott's ranch a Woot bed was seen. This bed was on fire near the point where it was measured.

Other localities, — On Otter Creek, a small tributary of Big Muddy Creek in the extreme northeast corner of the reservation, a bed of lignite outcrops but has been so completely burned t hat no satisfactory measurements could be made.

In the west bank of Big Muddy Creek 3 miles northeast of Scott's ranch several thin beds of lignite were noted, but they were not of sufficient thickness to warrant much attention.

From Kern's ranch, on Poplar River, about 9 miles north of the seventh standard parallel, northwestward to the north boundary of the reservation, the contact of the somber-colored beds with the overlying Fort Union formation is easily traceable and

56 Contbibutions To Economic Geology, 1908, Pabt Ii.

is usually marked by the presence of several beds of lignite, both above and below. From Kem's ranch southeastward to the seventh standard parallel the lower contact of the Fort Union is so generally concealed that its position is indefinite.

On Hay Creek, 3 miles north of Kern's ranch; lignite has been mined for local use. At the time the mine was examined only 3 feet 7 inches of the bed was exposed, the base being concealed. A thin parting occurs near the top of the bed.

The area in the northeast comer of the reservation underlain by the Fort Union formation is shown on the map accompanying this report. Although in this area lignite is exposed only along the large streams it is probable that prospecting elsewhere would reveal many workable beds now concealed by debris.

North-Central Part Of Reservation.

In the north-central part of the reservation, south of West Branch of Poplar River and Cottonwood Creek, is a high plateau whose north boundary is marked by an abrupt escarpment in which the contact of the somber-colored beds with the Fort Union formation above is exposed. This contact, at or near which several beds of lignite usually occur, is about 200 feet above the level of Poplar River. The land between the base of the escarpment and Poplar River has a uniform slope, but is in places deeply trenched by short northwardflowing streams. The highest part of the plateau lies next to its north boundary, from which the slope is gentle to the south for several miles, to a region where streams heading in the plateau gain sufficient strength to cut deep valleys, thus changing the character of the country from a smooth to a rolling prairie with gulches here and there.

The lower contact of the prolifically lignite-bearing formation on the south side of the plateau could not be located with certainty because of the smooth, grass-covered character of the country. The contact of the somber-colored bods and Fort lnion formation in this plateau rises gradually to the west to a point a few miles east of the head of Cottonwood Creek, where it is intercepted by a gravel terrace the grade of which, although in the same dinvtion, is slightly less than the rise of the contact.

Section at uhitf point at east rmi of plateau aouth of HV.tf Uranrh of Poplar River.

Ft, In, Siiiulstoiu>, nift , yellowish 40

Lijrniio 5

Lifnito 7

Olay 2 3

Fobt Peck Lignite Field, Montana. 57

Ft. In.

Clay and aand, somber 77

Lignite 4 5

Clay, carbonaceous 2 8

Lignite 1

Clay, gray 3

Sandstone, gray 17 5

Lignite 2 1

Clay, carbonaceous 2 3

Sand, clayey 20

180 10

Stdion in badlands soiUheast of junction of Cottonwood Creek and West Branch of Poplar

River.

Ft. In.

Gravel 15

Sandstone, coarse, white 2 6

Sandstone, yellowish, and gray clay 40

Lignite 5

Clay 6

Lignite 3

Sand, clayey 20

Sandstone, soft 10

Lignite 1

Sandstone, clayey 15

Clay, dark gray 40

Lignite 3 6

Clay 1 6

Lignite 5

Clay, sandy 4

Lignite 6 6

Clay 5

Sand 10

Clay, sandy, with two thin beds of lignite at lop 17 6

Lignite 1

Clay 12 6

Sandstone, cream-colored 5

Lignite 2

Clay 3

Sand, somber 15

Lignite 3 9

Clay, sandy, somber.

242 8

As shown by the sections, a number of lignite beds occur in tliis area . but they are ratlier inaccessible because of their elevati m. Water for mining purposes is scarce or lacking altogether.

58 Contributions To Economic Geology, 1908, Pabt U.

Section o/ somber-colored beds in badlands southeast oj Kem*s randi.

Ft. In.

Sand and clay 12

Lignite, bony 2 6

Sand, yellow 6

Lignite, thin

Sand 2 6

Lignite 8

Sand and clay 10

Lignite 1 3

Clay and sand 47 6

Lignite 2

Clay 10

Lignite 1

Sand 10

Lignite, thin

Clay and sand 28 6

Lignite 8

Sand and clay 66

Lignite, thin

Clay 17

Lignite 1

Clay, with two thin seams lignite 24

"241 7

North of Cottonwood Creek and between East and West branches of Poplar River are some small areas underlain by yellow beds of the Fort Union formation, but they are similar to the plateau just described so far as general conditions of accessibility are concerned and will not be discussed further. Their extent is shown on Plate III.

Section of lignite beds in NE. J sec. 6, T. tS N., R. 47 E.

Ft. 111.

Gravel and clay 15

Sand 5

Clay, sandy 8

Lignite 1 10

Clay 8

Lignite 1 10

Clay, sandy -20

Lignite 1 8

Clay 5

Lignito 1

62 9

The lignite beds noted in the foregoing section appear in a high point of lanc which is crossed by tlio seventh standard parallel just crist of Wolf Creek. A short distance northeast of the point where the section was made one of the beds noted has been mined for local use. About 40 acres of surveyed land is underlain by the lignite.

Character And Uses Of The Lignite.

The lignite in the Fort Peck field docs not differ in character and composition from that in other parts of the same general region. It is dark brown in color, tough, and woody in structure.

Fobt Peck Lignite Field, Montana.

The following analysis represents a sample of lignite obtained 3 miles north of Culbertson, which is the only place near the reservation where an unweathered sample could be obtained at the time, but it is thought that fuel in other parts of the field will not differ materially in quality from this sample. The analysis was made at the laboratory of the United States Geological Survey fuel-testing plant, Pittsburg, Pa.

Proximate analysis and calorific determinations of lignite from the Bruegger mine, 3

mUes north of Culbertsonj Mont.

[F. M. Stanton, chemist in charge.]

Laboratory No

Saniple as received:

Moisture

Volatile matter

Fixed carbon

Ash

Salphur

Calories

British thermal units.

28. W 3,333 6,999

Loss of moisture on air-drying. Air-dried sample:

Moisture

Volatile matter

Fixed carbon

Ash

Sulphur

Calories

British thermal units

5,437

0,787

This sample was taken according to Survey regulations and represents the whole thickness of the bed. After crushing, the Ugnite was sealed in a galvanized can and thus reached the laboratory in practically the same condition as it was in the mine. As shown by the analysis the sample as received at the laboratory contained 43.16 per cent of moisture, which is somewhat high even for a lignite. It .is probable that the analysis of the air-dried sample represents approximately the condition of the fuel as it would reach the consumer, for much of its moisture is lost through handling.

In the absence of timber, which is almost totally lacking in this region except in the river valleys, lignite is used generally for domestic purposes. However, as most of the inhabitants of the Fort Peck region live near Missouri River, where timber is comparatively plentiful, Uttle lignite is mined. Except at the Bruegger mine it is taken from open pits where it is necessary to remove only a small amount of overburden.

Future Development.

Lignite is widely distributed in this general region and it is not likely that any part of the area will develop far in advance of any other part, though if a certain field should have extremely favorable conditions of transportation, thickness, and purity of fuel it would derive some advantage therefrom. It seems probable, therefore, that the fuel will have only a local use for many yeara to come and that it will not enter seriously into competition outside of its own territory with better grades of fuel mined in other parts of Montana.

Probably the greatest future use of the lignite will be in generating power for pumping plants to irrigate lands where gravity systems are impracticable, but lands however irrigated Would attract many settlers, thus creating a great demand for fuel for domestic purposes.

The Central Part Of The Bull Mountain Coal

Field, Montana.*

By R. W. Richards.

Introduction.

Field work, — The sxirvey of the Bull Mountain coal field, Montana, which was begun during the summer of 1907 by L. H. Woolsey,* was continued during the month of May and up to the middle of June, 1908, by M. A. Pishel and the writer, and from that time until the 1st of November by Henry Hinds, Frank R. Clark, James H. Bridges, and the writer. The present paper is a preliminary statement of the results obtained in the area bordering the north and east sides of that portion of the Bull Mountain field examined and discussed by Woolsey. The residents of the region rendered valuable assistance and the Republic Coal Company materially aided the progress of the work by the contribution of information gathered by its prospecting parties.

The primary purpose of the survey, as in the previous season, was the collecting of data for the classification and valuation of public lands supposed to be coal bearing. The only investigation in the Bull Mountain coal field previous to that of 1907 was that of the geologists of the Transcontinental Survey in 1881.*= This was largely confined to the Mammoth coal bed, the discussion of which has been reviewed by Woolsey. The results of this earlier work, so far as identification is possible, agree closely with those obtained by the Geological Survey, but the work itself was carried on with much less detail.

Location and extent. — The Bull Mountain coal field is located in the southeast-central part of Montana, as may be seen by referring to the index maps of Plates IV and V. The field lies, roughly speaking, about 30 miles north of Billings, and is mainly bounded on the

a A full report on this coal field Is In prepnralion and will pu])Ilshfd as a separate' bulletin. 5 WooLsey, L. H., The Bull Mount4iin coal field, Monlana: Bull. V . S. Cleol. Survey No. 341, 1908, pp. 62-77. cEldridge, G. II., Montana coal fields: Tenth C'ensus, vol. 15, 1880, pp. 753-755.

Bull Mountain Coal Field, Montana. 61

north by Musselshell River. Two parts of the field, however, cross the river, one in the vicinity of Musselshell and the other near Roundup. The east boundary of the field is still more irregular and crosses the heads of Wild Horse and Alkali creeks about 12 miles east of Musselshell post-office, in R. 31 E. The south boundary is within T. 5 N.

The field as a whole is about 36 miles from north to south and 30 odles from east to west. The part treated in this report is L-shaped aod comprises about 612 square miles. It includes Ts. 5 and 6 N., Rs. 28 and 29 E.; T. 7 N., Rs. 25, 26, 27, 28, and 29 E.; T. 8 N., Rs. 25, 26, 27, 28, 29, and 30 E.; and portions of T. 9 N., Rs. 27 and 28 E. Roundup, the only mining town of the field, and the center of population, is situated on Musselshell River in T. 8 N., R. 25 E., about 2 miles northeast of a small trading point, formerly known as Roiindup post-office. It presents to-day a remarkable instance of the rapid growth of a coal-mining camp.

Commercial relations, — The Bull Mountain coal field has been brought into prominence by the building of the Pacific coast extension of the Chicago, Milwaukee and St. f aul Railway, now known as the Chicago, Milwaukee and Puget Sound Railway. This field is the most promising source of coal supply for this new transcontinental road, a fact which has led to its rapid development.

Butte, a mining and smelting center, and one of the largest consumers of coal in Montana, is entered by the line of railway passing through Bull Moimtain, and Roundup coal is being brought into this market on favorable competitive terms with coal from the other fields that up to the present year have supplied the industries of that city.

Billings, a large center of population, about 20 miles south of the southern edge of the Bull Mountain coal field and about 50 miles south of Roundup, derives its fuel supply mainly from the Red Lodge and Bear Creek districts, but direct railway connection between Roundup and Billings is a possibility of the future.

Drainage, — The Bull Mountain coal field occupies the higher portion of the main divide between Yellowstone and Musselshell rivers in Rs. 25 to 31 E. The streams draining the north side of the field and entering Musselshell River, named in order from west to east, are as follows: Goulding Creek, Naderman Coul6e, Half breed Creekj Berrigan Coulee, Parrot Creek, Schnall Coulee, Fattig Creek, and Hawk Creek. The principal creeks which enter Yellowstone River from the southeast portion of the field examined are Buffalo, Hibbard, Cow Gulch, and Railroad creeks. The streams on both sides of the divide are for the most part intermittent, but all of them have deep -cut valleys that are often flooded after heavy diowers.

Contributions To Economic Geology, 1908, Pabt Ii.

Topography.

The portion of the Bull Mountain field examined during the season of 1908 has an extreme relief of about 1,300 feet and exhibits a type of topography that is the result of rather mature erosion upon nearly horizontal beds of alternating hard and soft rocks. The traveler passing along the northern boundary of the field on the Chicago, Milwaukee and Puget Sound Railway sees to the south, in the background, high buttes, such as Three Buttes and the main northern Bull Mountain Mesa. Radiating from them in the midground he sees rugged divides which are dissected into mere skeletons by innumerable couI6es. In some places heavy horizontal sandstone strata produce extensive flats, which as a rule arc utilized for grazing purposes. In the foreground stretches the flood plain of Musselshell River, which where irrigated produces excellent crops of alfalfa and grain. Badland topography is uncommon and is limited to a band of sandy clay shale which outcrops near the base of the coalbearing rocks.

Geology.

Stratigraphy.

The upper rocks of the Bull Mountain coal field belong to the Fort Union formation of the Tertiary system. The lower rocks, which rest in apparent conformity upon the Bearpaw shale of the Cretaceous, have by previous writers been either referred to the Laramie or designated Hransition beds," between the Cretaceous and Tertiary systems. They are regarded as equivalent to the somber beds of the Miles City field. The upper 1,650 feet of the section contains an abundant fauna and flora, which have been identified as of Fort Union age by F. H. Knowlton and T. W. Stanton. The underlying 200 to 300 feet of somber-colored shale and coarse yellow sandstones, with beds of carbonaceous sandstone and shale, have yielded a few fossils of possible Fort Union age. The bottom portion of the section, comprising the doubtful Laramie or transition beds, is apparently barren of fossils and consists of alternating gray sandstones and clay shales with thin beds of coal.

Stratigraphy of the central of the Bull Mountain coal fields Montana.

System.

Tertiary . (?)

Formation.

Fort Union formation.

Thiclc. ness.

Feet. I.(i50

Dwcription.

Cretaceous .

Yellowish sandstones and shales interstratifled with lignite beds. 200-300 Somber-colored shale and coarse yellow sandstones, with beds of carbonaceous sandstone and shale. 1.480 I Alternating gray sandstones and clay shaleti with thin coal beds.

( Bearpaw shalo G ray to brown shales and clay.

[Laramie (t) formation

Bull M0Untai19 Coal Field, Montana. 63

A section of the lower beds is given below to show the proportions of the different rocks and the relative positions of the coal beds.

SeUon of lower rocks (Laramief) of the Bull Mountain coalfield, near MtuuUhell, Mont.

Sandstone, gray (base (7) of Fort Union). Ft. in.

Sandstone, yellow, coarse, soft 212 4

Bio Dirty Coal Bed.

Carbonaceous sandstone and shale, with |-inch to 1-inch

streaks of coal 10 5

Sandstone, yellow, soft 6 6

Carbonaceous sandstone and shale, with streaks of coal as

above 7 9

Sandstone, yellow, coarse, with iron concretions 15 4

Limestone 1

Sandstone 14

Coal 8

Shale, yellowish 30

Sandstone 15

Coal 4

Shale, gray 4

Coal 8

Shale, gray 34

Sandstone, with iron concretions 55

Limestone 3

Shale, gray 3 4

Coal 3

Bone ' 3

Coal 7

Shale .' 4

Coal 3

Sandstone, yellow, weathering into rounded forms 16

Shale 11 2

Coal 10

Limestone concretions 10

Shale 30

Sandstone 15

Shale 2

Homestead Coal Bed.

Coal 11

Shale, carbonaceous 9

Coal 1 1

Shale 1

Coal 11

Shale 1

Coal 6

Shale 18 6

Coal 1 8

Shale 6

Coal 2

Shale 4 7

Sandstone, ,,,,.,.,.,., , ,, . , 2

64 CONTBIBUTIONS TO ECONOMIC GEOLOGY, 1908, PABT n.

Ft. in.

Shale 4

Coal, bone 2

Coal 1

Shale 10 9

Coal 3

Shale 5

Sandstone 10

Shale 1 6

Coal 1 6

Shale 10

Sandstone 16

Shale 10

Coal 10

Shale 2

Sandstone, with limestone cap 13

Shale 41

Sandstone, yellow, coarse, with limestone cap 40

Shale 179 6

Sandstone 40

Shale 92 6

Sandstone, yellow and gray 5

Shale 74

Sandstone, yellow to gray, weathering to rounded pebbles. . . 30

Shale, caky, with thin limestone bands 389

Sandstone, calcareous 3

Shale 80

Sandstone 15

Sandstone, yellow, porous

Concealed

Sandstone, brown, thin-bedded

Shales, clay, gray to brown (Bearpaw ahale).

1, 777 8

The character of the rocks which were identified as Fort Union and which constitute the upper portion of the Bull Mountain section is illustrated graphically in the columnar sections on Plates IV and V, This section, which is a .ncralization of several sections measured on the north and southeast sides of the mountains, differs from that published by Woolsey for the southwest portion of the field chiefly in the intervals between certain coal beds. The most noticeable difference is the thickening of the beds near the base of the section by about 450 feet.

Structure.

The central part of tlie Bull Mountain field has a comparatively simple structure. It consists of a large, shallow synclinal basin, having a general northwestward axial trend, and a rather accentuated lip at its northwestern extremity. The syncline merges on its

a Op. Cit.

Bull Mountain Coal Field, Montana. 65

northern border into a mild anticline whose flanks dip about 5. The anticline is parallel on the north by a smaller but sharper syncUne, the greater portion of which hes to the north of the area shown on the accompanying maps.

Coal.

General Statement.

The coal of the Bull Mountain field is for the most part high-grade Bubbituminous C black lignite") or low-grade bituminous. Mining has not been carried on for a sufficiently long period to observe the coal under all conditions of exposure, and thus to determine accurately its ''stocking" quaUties. If the coal proves to stock well it should probably be classed as bituminous coal. Twenty coal beds that in places attain a thickness of more than 2 feet were studied. The general habit of the beds is lenticular, though several beds are notable exceptions to this rule, and it has been possible to trace their outcrop completely around the mountains. An attempt was made to locate and define the workable portion of the beds by a study of the outcrop, supplemented by drill sections in the northwestern part of the field. The ravines, coulees, and ridges were carefully searched for outcrops of coal. All coals thus discovered were traced and those having a thickness of 2 feet or more were mapped. The traverses of the coal outcrop were made either by compass and pacing or by triangulation, according to the character of the topography. All traverses were tied to land comers. The position of these comers was assumed in general to be correctly given on the maps of the land surveys except along the right of way of the Chicago, Milwaukee and Puet Sound Railway, where the railway survey, being later than the land survey and doubtless more accurate, was accepted. Certain gross inconsistencies in the position of land comers were evident even by the method of work pursued, and these are shown on the maps. These maps indicate the number and character of the comers found, an effort being made to distiiuish between government comers, doubtful government comers, corners reported by the railway survey but not visited by members of the party, and comers established by private individuals. The outcrops of the principal coals are platted in soUd, broken, and dotted lines, which represent within certain rough Umits the thickness of the coal beds and the position of the outcrops with reference to section comers.

Detailed Descriptions.

In this discussion the coals will be taken in order, beginning with the lowest bed and continuing upward to the highest bed in the Bull

TOeS**— Bull. 381—10 5

66 Contributions To Economic Geology, 1908, Part Ii.

Mountains proper. Named in this order, the principal coal beds are the Homestead, Big Dirty, Carpenter, SpendifF, Snyder, Snelling, Roundup, Wildhorse, ''C. A.," Buckey, Chandler, Dougherty, Ostrander, Pompey, Saddler, Mammoth, Rehder, Rock Mesa, Carter, Matt, Bull Mountain, Wescott, Strait, Red Butte, Fattig, and Summit.

The thickest and probably best coal of the doubtful Laramie rocks has been called the Homestead bed. The following section, measured in a prospect, illustrates the character of the bed :

Section of Homestead coal bed, in T. 9 N., R. 27 E.

Ft. in.

Shale with coal streaks 2

Coal , 1 3

Bone 4

Coal 4

Bone 2

Coal 3

Shale 1

Coal 1 1

Total coal 2 11

The sample of coal which was taken at this point from the 1-foot 3-inch bench at the top of the bed gave a calorific value of 12,116 British thermal units in the air-dried state, and on this basis alone the coal may be considered a high-grade subbituminous or possibly a low-grade bituminous. The coal, although almost freshly mined, showed marked indications of weather checking. The Homestead bed and its companion thinner beds were deemed unworthy of mapping in the field, and may be dismissed without further discussion.

The Big Dirty coal bed, called by Woolsey the Glendi ve bed, is not workable in the Bull Mountain field, but in places it produces conspicuous outcrops (P coal, Pis. IV and V) and makes a useful marker by which to limit the area of coal-bearing rocks. In order that this bed may not be confused with any of the valuable coals, its distribution and character will be fully treated.

In the southeastern portion of the field the Big Dirty coal bed does not outcrop continuously, but its blossom was found in the southeast comer of T. 5 N., R. 28 E., and near the southeast comer of supposed sec. 23, T. 5 N., R. 29 E. (unsurveyed), the bed consists of 3 feet of carbonaceous shale and sandstone. It outcrops conspicuously along Cow Gulch, in the southeastern part of the township, where it consists of about 4 feet of carbonaceous shale. Outside of the area mapped during the present year this coal was seen in the

a Woolsey, L. H., op. cit., p. 66.

Bull Mountain Coal Field, Montana. 67

southeastern portion of T. 5 N., R. 32 E., on BnflFalo Creek, and at this point consists of 20 feet of carbonaceous shale and sandstone, with thin streaks of coal. The Big Dirty coal bed has not yet been examined between this point and the center of T. 9 N., R. 30 E., where it is exposed as 11 feet of carbonaceous shale and sandstone, with the characteristic thin, irregular streaks of coal. In sec. 18, directly north of D. Chandler's prospect on the Carpenter coal, the Big Dirty thins to about 5 feet. The outcrop continues westward along the northern rim of the Fort Union basin, and was measured in the northwestern portion of T. 9 N., R. 28 E., where it shows two benches of carbonaceous shale and sandstone 4 and 3 feet thick, containing thin seams of coal and separated by a parting of sandstone 2 feet 6 inches thick. The outcrop continues nearly due west from this point to the northwest comer of the township, where it rounds the end of the syncline and takes a nearly southwest course. The bed as measured in sec. 20, T. 9 N., R. 27 E., consists of 5 feet of carbonaceous sandstone and shale, with thin seams of coal and 1 foot of dirty coal at the base. The outcrop crosses Musselshell River in the northeastern part of T. 8 N., R. 27 E., and thence runs approximately west, aside from the irregularities due to the topography. A prominent outcrop may be seen in the railway cut in sec. 3, one-half mile east of the Arkwright Sheep Company's ranch, where a thickness of about 6 feet of coaly shale is exposed. To the west, in sees. 5 and 6, the outcrop is very conspicuous, as it covers a dip slope for a considerable distance. Although it was not possible to obtain an actual measurement of the bed in this part of the township, it appears to be at least 20 feet thick and is composed of alternating carbonaceous shales and sandstones, with thin layers of coal. Fragments of the eroded coal collect in the coulees and appear to be of a fairly good quality. The outcrop continues across the next township to the west in the same general w-esterly direction and is well exposed at some places, especially in sec. 2, north of the river road, in an isolated butte. At this point it shows at least 2 feet of dirty coal. There is a more prominent outcrop in sec. 9, where the bed, 6 feet thick, is exposed in a railway cut. The amount of coal, however, is small and carbonaceous shale and sandstone predominate. In sec. 18 the bed is 10 feet thick, but consists mainly of dirty coal and carbonaceous shale. In T. 8 N., R. 25 E., the outcrop of the Big Dirty bed swings toward the northwest from a point in sec. 14 about 1 mile west of Roundup. The thickness in this township, as shown by aeveral measurements, is about 10 feet, but the interbedded carbonaceous shale and sandstone predominate over the coal. The bed was next observed in the township to the south, where it out-

68 Contributions To Economic Geology, 1908, Pabt Ii.

crops near the EIso schoolhouse. The following section was measured at this point:

Section of Big Dirty coal bed, near Elso schoolhouse, in sec. 7, T. 7 N., R. t5 E.

Feet.

Carbonaceous shale, sandstone, and coal 6

Shale 2

Carbonaceous shale, sandstone, and coal 4

In the township to the west (T. 7 N., R. 24 E.), the Big Dirty coal bed outcrops on Kem Creek at two points. At the upper locality, which is about 4 miles from the last-mentioned section, it has the following composition:

Section of Big Dirty coal bed, in T. 7 N., R. U E.

Ft. In.

Shale, bituminous, with streaks of coal 2 II

r. 10

Dirt 8

Bone J

Coal 6

Shale, bituminous 5

Coal 3

Shale, bituminous 1 5

Coal 5

Shale, bituminous 10

Coal i

Bone 2

Clay, sandy 6

Coal 3

Total coal 2 3i

The lower outcrop on Kem Creek about 2 miles from its mouth shows 2 feet of coal near the bottom of the bed. Coal taken from the bed at this point has been used by several ranchers with fairly good results, but it contains a large amoimt of ash and slacks in a short time. The probability of a bed of this character improving with depth or distance back from the outcrop is too remote to be considered, and capital expended in its development would undoubtedly be wasted.

Tlic Carpenter coal is named from the creek on which it is mined in T. 9 N., R. 30 E. Tliis bed is 450 feet stratigraphically above the Big Dirt} coal bed. The main outcrop extends along the northern and eastern edges of the Bull Mountain field, and although it was not examined in detail, certain general statements concerning it can be made.

Tlie C-carpenter coal bed has the following section at W. C. Grant's opening in sec. 26, T. 9 N., R. 30 E., which may be considered typical of the thicker portion of the bed.

Bull Mountain Coal Field, Montana. 69

Section of Carpenter coal on Carpenter Creek.

Ft. In.

Coal, and some mineral charcoal 5

Coal I 1

Shale IJ

Coal, with six inch partings 2 11

Total coal 0

It thins gradually to the west; in T. 9 N., R. 29 E., it averages about 4 feet in thickness and in T. 9 N., R. 28 E., so far as could be observed, it is less than 2 feet thick. A closed outcrop of coal about 2 feet 8 inches thick which may belong to this bed is exposed on Fishel Creek in T. 8 N., R. 29 E., about three-fourths of a mile above August Schrader's ranch.

Bore-hole information in the vicinity of Musselshell post-office shows that the bed thins toward the south. The thickness of the bed and its position in the section indicate that the coal of the Fishel Creek locality may be safely correlated with the Carpenter coals. An exposure of coal which is probably an outcrop of the Carpenter bed was seen in the northwestern part of T. 7 N., R. 31 E. At this point, as the following section shows, the coal is separated into four benches by partings.

Section of Carpenter coal bed in T.7N.,R. SI E.

Ft In.

Coal 6

Sandstone, bituminous

Coal 1 2

Shale 2db

Sandstone 26

Shale 2db

Sand 1 2

Coal 1 2

Shale 1 11

Coal 1 7

The partings appear to thicken toward the southwest, but no measurements were taken showing more than 2 feet of coal. The better portion of the Carpenter coal bed therefore appears to lie in Tps. 8 and 9 N., Rs. 29 and 30 E. Further work is necessary, however, to determine the exact conditions imder which these beds occur in the northeastern portion of the field. An analysis of a sample of the Carpenter coal given in the table on page 79 shows a calorific value somewhat lower than that of the Roundup coal.

Between the Carpenter and Roimdup coal beds on Fattig Creek a number of thin coal beds, the Snelling, Snyder, and Spendiff (Ob, Oc, Od coals, PL V), locally show sections having from 1 to 3 feet of

70 Contributions To Economic Geology, 1908, Pabt Ii.

coal. These beds are, however, relatively unimportant and do not merit further discussion.

The Roundup coal bed is about 600 feet stratigraphically above the Big Dirty coal bed, and at present is commercially the most important coal in the field, as all the active mines, namely, shafts Nos. 1 and 2 of the Republic Coal Mining Company and the Commercial mine of the Roundup Coal Mining Company, are located upon this bed. The coal is at present mined only in T. 8 N., R. 25 E. (Oa coal, PL V), but an abandoned prospect formerly operated by W. C. Grant in T. 8 N., R. 29 E. is apparently located on the same bed.

The westernmost outcrop of the Roundup coal near the north boimdary of T. 7 N., R. 25 E., presents a scarcely workable section, but in sec. 33, T. 8 N., R. 25 E., it is thicker, as shown below:

Section of Roundup coal bed in sec. SS T. 8 N. R. 25 E,

Ft. in.

Coal 2

Sandstone 1

Coal 1

Shale 1 8

Coal - 1 6

Total coal 2 8

From this point the outcrop runs nearly due north to Musselshell River, north of which for about a mile it swings to the west, and thence extends roughly northward (except for irregularities due to the topography) to the nose of the main Bull Mountain syncline in sec. 8, T. 8 N., R. 25 E. A typical section along a portion of the bed is given below:

Section of Roundup coal bed in sec. 16 T. 8 N., R. 25 E.

Ft. In.

Bone 3

Coal 6

From this locality it runs nearly southeast to the Commercial mine of the Roundup Coal Mining Company, where the bed is reported to attain a maximum thickness of 6 feet. About half a mile to the southeast, however, in a slope in the NW. J NE. J sec. 23, it contains only 4 feet of coal, but the thickness increases toward the southeast so that in the Republic mine No. 1 it ranges from 5 feet 9 inches to 6 feet 1 inch and has a rather constant roof of about 4 to 6 inches of bituminous shale, overlain by heavy sandstone.

The next opportunity to examine tlie bed is in sec. 18, T. 8 N., R. 26 E., about one-eighth of a mile west of J. W. Newtons ranch, and here, owing to the burning, it is impossible to make a careful measurement of the coal. It is at least 5 feet thick. From this point

Bull Mountain Coal Field, Montana. 71

the outcrop is projected across the flood plain of the river to an exposure in sec. 17, where the bed shows the following section:

Section of Roundup coal bed in sec. 17 y T, 8 N.y R. 26 E,

Ft. in.

Coal 3i

BoDe i

Coal 3 7

Total coal 3 lOJ

Near Berrigan Coulee the character of the section begins to change, a portion of the coal being replaced by carbonaceous shale. The amount of shale seems to increase gradually toward the east to a certain point and then to decrease to the east fork of Parrott Creek, where the following section was measured:

Section of Roundup coal bed in sec. 79, T. 8 N., R. 27 E.

Ft. in.

Coal 3

Shale 3

Shale, carbonaceous 4

Coal 3 3

Total 3 6

The coal bed at this point seems to have recovered its characteristic features and the coal maintains the same quality and thickness to Fattig Creek. On the west side of this stream the following section is exposed :

Section of Roundup coal in sec. S2j T. 8 N.j R. 28 E.

Ft. In. Shale, carbonaceous 8

Coal 5

Shale 1

Coal 1

Shale i

Coal 7i

Total coal 2

From this point eastward the coal undergoes a rapid deterioration into shale and decreases in thickness until it measures only 1 foot 6 inches in sec. 28, T. 8 N., R. 28 E.

The Roimdup coal ranges in quality from a high-grade subbituminous to a low-grade bituminous, and has a calorific value of more than 10,000 British thermal units in the air-dried sample. It is a good coal for steam purposes and appears to withstand shipment well if mined under sufficient cover.

The Wildhorse coal is relatively unimportant in the area examined, although its eastern continuation from the point where the bed crosses the east boundary of T. 5 N., R. 27 E. (O coal, PI. IV), was

72 CONTRIBUTIONS TO ECONOMIC GEOLOOT, 1906 PART n.

mapped and numerous measurements were obtained, of which the following is representative of the thicker portion of the bed:

Section of WHdhontr auil bfdin sec T. Ji .V., K. :i8 E. {unsiirveyed).

Ft. In.

Coal 2

Coal, with t-inrh to J-inch RtroakR of shale 4

Coal 2 9

2 U

On the north side of the Bull Mountains the Wildhorse bed where present is represented by less than 2 feet of coal. It is possible that in the development of the field the Wildhorse and Roundup coal beds will be found to be identical, although the evidence in hand does not warrant that interpretation.

The "C. A.*' coal is 95 feet above the Wildhorse coal bed and persistent in the southeast portion of the field. It reaches its greatest thickness in sec. 36, T. 6 N., R. 28 V.. (Na coal, PI. IV), thinning both to the west and to the east. It is of poor quality, appearing on the outcrop to nearer lignite than subbituminous, and is characterized by a very persistent parting, as shown in the following typical section :

Section of'C.Ar coal in mc. P, T. 5 N., R. 28 E.

Ft. In.

Coal 6

Shale 6

Coal 1 6i

Total coal 2 (

The Buckey coal occurs 60 feet above the "C. A." bed, and though prominent in the area examined in the previous year by Woolsey is of slight importance in that portion of the field mapped during 1908. The bed shows a workable thickness for a short distance along the western border of T. 5 N., R. 28 E. (N coal, PI. IV), but nowhere exceeds 2 feet 6 inches in thickness.

Between the Buckey and the Dougherty coal the rocks are gwaerallv barren of coal beds. The Chandler coal, 40 feet below the Dougherty, was found near Railroad Creek, Cow Gulch, and Fatt% Creek. It is usually thin and of poor quality.

The Dougherty coal is persistent throughout the area examined and is workable except in T. 8 N., R. 26 E. (M coal. Pis. IV and V), and portions of T. 7 N., Rs. 26 and 27 E. It is 510 feet stratigrapliically above the Roundup coal, as determined by a leveled section near Fattig post-office and a bore-hole section in T. 7 N., R.. 26 E., on the west fork of Parrott Creek. A typical section of the workable portion of the in sec. 17, T. 7 N., R. 26 E., in the northwestern part of the field shows 3 8 inches of coal.

r

BUIiL MOUKTAIN COAL TIELD, MONTANA. 73

According to ' information gathered from the bore holes the bed appears to thin in the eastern part of the same township, but to the north the measurements on the outcrop range from 1 foot 6 inches to 2 feet 1 inch. In a section in T. 7 N., R. 27 E., on one of the forks of Parrott Creek, it again increases in thickness.

SeeUon of Dougherty coal in tec. S2, T. 7 N., R. n E.

Ft. in.

Coal 2 6

Shale 4

Coal 2

Total coal 2 8

The shale parting of the above section is persistent and thickens eastward to a maximum of 9 inches. The following section is representative of the coal bed near the head of the dry fork of Hawk Creek:

Section of Dougherty co€d in $ec. .5, T. 6 N., R. t9 E. {unturveyed).

Coal

Shale

Shale, bitiiminouB

Coal

Total coal 3 7

The sections to the west of this point show a gradual increase in the thickness of this coal until the maximum is apparently reached in Cow Gulch, where the following measurement was made:

Section of Dougherty coal bed in mc. 10, T.S N., R, t8 E.

Ft. In.

Coal li

Shale 1

Coal : 4 9

Ft.

In.

Total coal 4 lOJ

From this point the outcrop takes a general southwesterly course and the bed is extremely variable in thickness, thinning to 1 foot 6 inches in sec. 20, T. 6 N., R. 28 E., but in sec. 21 reaching 2 feet 1 1 inches. At a point where the south fork of Railroad Creek enters the township it shows the following section:

Section of Dougherty coal bed in sec. ,W, T.6N., R. 28 E.

Ft. In.

Coal, poor 1

Coal 2 i

Shale 1

Coal 6i

Shale 4

Coal 1

Total coal 2 9

74 Contributions To Economic Geology, 1808, Pabt H.

The coal of the Dougherty bed is undoubtedly high-grade subbituminous and appears to be one of the cleanest and most uniformly thick coals of the field. A sample taken from the outcrop at Cow Gulch showed, after being air dried, a calorific value of 10,771 British thermal units. The Dougherty coal generally has an excellent sandstone roof and a shale floor, two valuable factors which, together with its quality, should lead to early development of this bed.

About 60 feet above the Dougherty coal in Rs. 28 and 29 E., the Ostrander coal (La coal. Pis. IV and V) is persistent and, thou commonly thin, it locally assumes a workable thickness, as shown in the following representative section:

Section of Ostrander coal bed in sec. 16, T. 6 N., R.28 E.

Ft. In.

Coal 6

Bone 2

Coal 3

Total coal 3 6

The same coal in the northern part of the field, in T. 8 N., R. 26 E., where measurements have been obtained, ranges from 1 foot 4 inches to 3 feet.

The Pompey coal, one of the most promising in the southwestern part of the Bull Mountain field, is apparently absent in the area covered by this report.

In the northeastern part of T. 7 N., R. 27 E., on Parrott Creek, the Saddler coal bed (Ka coal, PL V) occurs about 40 feet below the Mammoth bed and ranges in thickness from about 1 foot 6 inches of coal to a maximum of 2 feet 2 inches. In the remainder of the field this bed is thin except at a point almost directly north of the easternmost of the Three Buttes, where it shows the following section:

Section of Saddlrr coal bed in sec. S2, T.7N., R. 28 E.

Ft. In.

Coal 1 6

Shale.: i

Coal 2 5

Total coal 3 11

The Mammoth coal bed (N coal. Pis. IV and V) is the thickest bed occurring in any part of the field so far examined. The portion mapped during the present year, combined with that given by Woolsey," closes the outcrop around the Bull Mountains.

The Mammoth coal bed was examined by Eldridgt\* and while, in general, results similar to his wen* obtained by the Geological

o Woobey, L. H., op.cU., pp. 00-75.

ft Eldrldge, G. H., Montana coiU fkKts: TVnlh iViksiis. \ol. iwi. pp. 7M-:&5.

Boll Mountain Coal Field, Montana. 75

Survey party, yet different interpretations have been given to some of the facts. For example, the outcrop is shown on the ac4*.ompanying maps (K coal, Pis. IV and V) as extending not so far east as on the earlier map of Eldridge, and in the northwestern part of the field the coal bed now called the Rehder is undoubtedly what Eldridge designateii as the upper bench of the Mammoth. It is clearly possible that Eldridges interpretation may be correct and final determination must await the development of mining. The Mammoth coal bed is undoubtedly workable throughout the part of its area mapped in 1908, although a number of small partings are invariably present and here and there reach such a thickness that it is difficult to decide from the section whether portions of the same bed or distinct beds are represented. For example, in the excellent exposure at Schlaberg camp, on Fattig Creek, a parting enters and thickens at the rate of 3 feet in 100, and yet the same parting measures only 10 feet 6 inches 6 miles distant at Douglas camp, on Cow Gulch, where the section given below was measured:

Section of Mammoth coal bed in 9ec. 10 T. 6 N., R. t8 E,

Ft. In.

Coal 8 6

Shale 3

Sandstone 2

Shale 6

Sandstone, gray 10

Shale 6

Coal 2

Shale 1

Coal 3

Total coal 13 6

This section was sampled for analysis and the upper bench gave a fuel value of 11,610 British thermal units and the lower bench 10,771 British thermal units in air-dried samples.

The extensive burning of the coal along the outcrop of the Mammoth bed, especially on both sides of the divide between Parrott and Halfbreed creeks, makes it difficult to obtain sufficient measurements to estimate the content of the coal bed in the northwestern part of the field. The effect of the burning itself, however, may be taken as a rough indication of the thickness of the coal bed, and it may be safely assumed that the bed is at least 3 feet thick inside of the burnt zone, which is probably not over 200 feet wide.

The Rehder coal bed (J coal, PI. V) occurs about 35 feet higher in the geologic section than the Mammoth bed, and is practically limited in distribution to T. 7 N., R. 26 E., and the southwest quarter of T. 7 N., R. 27 E. The outcrop is extensively burned, a fact

76 Contbibuttons To Economic Geology, 1908, Part H.

which renders it difficult to obtain satisfactory measurements. However, the following is believed to be a representative section:

Section of Rehder coal bed in sec. 12, T. 7 N., R. 26 E,

Ft. In.

Coal 3

Bone 1

Coal 11

Total coal 3 11

About 45 feet above the Rehder coal, or 80 feet above the Mammoth coal, there is a persistent but erratic coal bed called the " Rock Mesa" coal (I coal, PI. IV). This bed is everywhere present in the southwestern portion of the field, as it is in the area examined in 1908, and in both localities it contains persistent partings which within short distances are likely to attain proportions deleterious to the commercial value of the coal. This bed is usually covered by a shale roof. The following section is typical for T. 7 N., R. 26 E.:

Section of Rock Mesa coal bed in sec. 27 y T.7 N., R.£S E.

Ft. In.

Coal 1 7

Shale 2

Coal 10

Total coal 2 5

In T. 7 N., R. 27 E., the maximum observed thickness of the coal is 3 feet 7 inches, which occurs in sec. 20, but there are many places in this township where the bed contains only small amounts of coal or the outcrop is obscured by grassed and forested slopes. In the eastern part of the field the Rock Mesa coal ranges from less than 1 foot 6 inches to a maximum of 3 feet 4 inches, but in most places it is less than 3 feet thick.

On the east side of the Three Buttes, about 50 feet above the Rock Mesa bed, is a coal bed which has been named the Carter coal (Ha coal. Pis. IV and V). This bed shows a thickness of 2 feet 8 inches in sec. 9, T. 6 N., R. 28 E., at the head of Cow Gulch, but thins in both directions, and so far as known is unimportant elsewhere.

Between the Carter coal and the Bull Mountain coals is the Matt coal, which attains some importance in the southwestern part of the field, but the measurements obtained in the area treated in this report were less than 1 foot, so that the bed need not be considered here.

The Bull Mountain coals (F and G coals, Pis. IV and V) in general outline the high mesas and buttes in the south-central portion of the field, and occur at a distance of about 130 feet above the Rock Mesa coal. This interval is 85 feet less than that observed by Woolsey in the southwestern portion of the Bull Mountains.

Bull Mountain Coal Field, Montana. 77

The two Bull Mountain beds are separated by only 12 to 20 feet of sandstone and shale. The upper bed is usually imderlain and overlain by conspicuous dark-gray clay shale 20 to 30 feet thick. The upper bed is in most places the thicker of the two and the following may be taken as an average section of both coal beds:

Section of Bull Mountain coals in sec. 15, T. 6 N., R. 28 E.

Ft. in.

Coal (F) 4 5

Shale 12

2 11

In many places one of the beds, usually the lower one, falls below 2 feet in thickness, and here and there both beds are thin and of doubtful value.

The coal-bearing area lying above the Bull Mountain coals is small, but comprises a number of beds (A, B, C, D coals, PL V) spaced at intervals of 15 to 60 feet. Many of these beds have probably lost a large part of their coal from burning, which baked and reddened the tops of the high buttes and mesas, so that thorough prospecting is necessary to locate the undestroyed portions. These higher coal beds are relatively inaccessible and therefore unimportant at the present time. The names, intervals, and known relative importance of these coals is shown on the maps and in the columnar section, except a small outlier in the Three Buttes section of the field, which was not mapped because of its insignificant area.

Character.

Physical Properties.

The coals of the Bull Mountain field are pitch black to brown black in color and when rubbed on unglazed porcelain leave a darkishbrown to black streak. They commonly show lustrous bands which vary in character, ranging from dull waxy or bright submetallic on a fresdi fracture to a dull satiny luster in the parts of the coal bearing mineral charcoal, or "mother coal." The waxy and bright bands range from less than one-eighth inch to over 1 inch in thickness.

Joints have been observed in all the coal beds where thev are well exposed. The joint planes are parallel to joints in the roof, many of which are continuations of those in the coal. The joint planes are in general nearly at right angles to each other and in places constitute well-defined face and butt cleats, so that the coal when shot down in the mine falls in roughly cubical blocks. The lumps of coal show a tendency to break up into smaller cubes on exposure to the atmosphere. Some of the banded coal on continued exposure disintegrates into platy flakes, while that which lacks the banded structure resists the process of disintegration for a longer period, but in nearly all cases

78 Contbibutions To Economic Geology, 1908, Part Ti.

finally breaks up by checking off in small chips with conchoidal surfaces. A net of pyrite or marcasite, together with their alteration products, and fine powdery gypsum is occasionally foimd along the joint planes. When the coal is broken by a blow from a hammer conchoidal to smooth fracture surfaces are Ukely to predominate over cleavage surfaces parallel to the joint planes. The coherence ranges from brittle to tough, and the impact is dull rather than metallic. The texture of the coal is dense to laminated and only in a few places shows sUght indications of a woody character. The coal is of low specific gravity. The accessory substances fall into several groups — sulphides, sulphates, and hydrocarbons. The sulphides, marcasite and pyrite, have already been noted. In addition to gjrpsum, the sulphate mentioned above, epsomite has been found in fairly large quantities in connection with some of the higher coals, especially the lower Bull Moimtain (G) coal. With this particular coal the epsomite forms a surficial deposit attaining a maximum thickness of about a foot directly imderlying the coal bed in sec. 8, T. 6 N., R. 28 E. Resin and sulphur are locally present in small rounded masses irregularly and sparsely scattered through the coal. The coal bums with a yellowish flame of moderate length and occasionally gives off a strong, pungent sulphurous odor. In burning the coal decrepitates rapidly, and when used in locomotives the fragments blow out of the stack or fall between the grate bars. These difficulties have been overcome to a considerable extent, however, by modifying the character of the forced draft and by using specially constructed grates. It is advisable to admit a rather large amount of air above the grate and also to distribute the coal unevenly upon the grate to prevent choking the process of combustion. The ash is fine, ranges from gray to reddish-yellow in color, and is not clinkery unless the coal is dirty.

Chemical Properties.

As the examination of the Bull Mountain field was practically limited to a study of the coal outcrops it was not possible to collect more than a few imweathered samples for analysis, owing to the lack of mining developments. The samples were collected in conformity, as nearly as possible, with the regulations of the United States Geological Survey, and the analyses were made imder the direction of F. M. Stanton at the Pittsburg laboratory. An examination of the coals as received from the mine shows that the moisture content ranges from 12.69 to 22.77 per cent, the amount of ash from 4.15 to 7.70 per cent (exclusive of Roundup No. 6235, a bore-hole sample whose high ash is due to the inclusion of rock dust), and the British thermal units from 8,863 to 11,034. The only strictly fresh sample (Roundup No.

Bull Mountain Coal Field, Moniana.

5900) heads the list and the Carpenter sample (No. 7197) foots it. The last sample was taken under very thin cover, and probably represents a weathered condition of the coal, not apparent on visual examination. The loss of moisture on air drying ranges from 2.70 to 16.30 per cent, the minimum representing an unweathered facies and the maximum a sample taken on the outcrop of the Dougherty coal.

Anafytii of coal 9ample$/rom the Bull Mountain fields Montana,

[F. M. Stanton, chemist in charge.]

Name of ooal bed .

Laboratory No.

Sample as leoeiTed:

Volatile matter. Fixed carbon.

M

Alr-fled sample:

Moisture

VdatUe matter...

Fixed carbon

[Siilphur

Elydiogen

Carbon

Nitrogen

British thermal units.

Nitrogen.

Oxygen. CaloiteB British thermal units.

Loss of mototore on air drying.

Thkknesi of bed (total coal). Thlcknesi of part sampled. . ,

7a32

6,731

12,116

Fl. in. 1 3

ia72

5,603

10,247

ia27

6,300

11,340

10,000

Ft. in.

Ft. in.

Ft. in. 5?

6,122

11,020

Ft. in.

5,984 I 10,771 I

Ft. in. i 4

11,610

Ft. in. 5 ,

6,558 11,804

Ft. in.

6829. Upper 1 foot 3 Inches of Homestead coal bed, about 12 miles northwest of Musselshell post-office. 7197. All except upper 9 inches of Carpenter coal bed about 6 miles east of Musselshell post-office. 5800. Full thickness of Roundup coal bed. SW. i NE. i sec. 23, T. 8 W., R. 25 E.

6235. Full thidmesB (7) of Roundup coal oed, bore-hole sample, T. 6 N., R. 26 E.

7196. Full thiclmesB of Roundup (7) coal bed, about 6 miles south of Musselshell post-office.

6830. Full thickness of Dougherty coal. NW. i 8E. sec. 10, T. 6 N., R. 28 E.

6828. Full thtekness of kmer bench of Mammoth coal bed, SW. NW. sec. 10, T. 6 N., R. 28 E.

6831. Lower 6 feet of upper bendi of Mammoth coal bed, SW. i NW. sec. 10, T. 6 N., R. 28 E.

A better comparison of the coals can be made from the analyses on the air-dried basis and in these the moisture ranges from 4.52 to 10.70 per cent and the British thermal units from 10,000 to 12,116. As there is good reason for behaving that the other coals will approximate the Roundup coal when sampled under mine conditions, the Roimdup may be taken as a type of the Bull Mountain coals. If compared with several coals from adjacent fields, on the basis of the data in the following table, the Roundup coal ranks well, especially in total carbon when considered apart from its ash and moisture.

Contbibutions To Economic Geology, 1908, Part Ii.

Comparigon of various Montana and Wyoming coals.

Rounda

Red

Lawistown

Lawistown

Sheridan (Carney ville)

Air dried.

Ash free.

Labora-

tory No.

Molstp ure.

Ash.

Fixed carbon.

British

thermal

units.

Mobture.

Total carbon.

ia27

11,340 10,270 11,444 11,663 10,670

10,096

6LQa

British

thermal

units.

12,814 11,746 12,780 12,712

10,648

Roundup

Red Lodge

Bear Creek

Lewistown

Lewlstown

Sheridan (CarneyvlUe)

Labora tory No.

Ash and moisture free.

Total carbon.

8a 71 8a 00

Total hydrogen.

a04608

British

thermal

units.

13,860 12,714 14,288 12,441

12,777

Ratios, air dried.

Fuel.

C/H.

n.7 n.o

ia4

C/0.

Los

Development.

Coal mining in the Bull Mountains is restricted to the Roundup bed in the northwestern part of the field, on Musselshell River and a fork of Halfbreed Creek. The thriving town of Roundup is an indication of the rapid development of the coal-mining industry. Early in the eighties coal of workable thickness was known here and a carload was taken out by WilUam Crane and shipped to Marcus Daly at Anaconda, but not until 1907 was commercial mining begim. In the fall ol that year the Repubhc Coal Company attempted to work the Roundup bed by a slope extending under the Musselshell River, but the cover, consisting mainly of alluvium, permitted the entrance of great quantities of water, which rendered this plan imfeasible. A shaft on the south side of the river, in sec. 24, T. 8 N., R. 25 E., which had been originally intended for an air shaft, was enlarged and used as the main shaft for mine No. 1. The coal was penetrated at a distance of 137 feet from the surface and is mined by the room and pillar method. Mule haulage is used underground. The mine is equipped with a complete pumping, hoisting, and loading plant. The coal as it comes from the mine is clean and is used mine run, or stored in pockets that feed directly into coal cars. The joints in the overlying rocks are charged with water, which flows into the new workings until exhausted. The water that thus drains into the mine has, however, been successfully handled by the pumps. This

Bull Mountain Coal Field, Montana. 81

water is of excellent quality and will probably be utilized by the town of Roundup. The production of mine No. 1 for 1908 is reported to have been 39,348 tons.

During 1908 the RepubUc Coal Company acquired coal rights in sec. 36 of the same township and started operation on mine No. 2 near the center of the section. The coal is reported to have been encountered in the main shaft at a depth of 347 feet from the surface on March 11, 1909, and is said to be 5 feet thick at this point. An extensive pimiping, hoisting, and loading plant is under construction. Mine No. 2 has been connected with the main line of the Chicago, Milwaukee and Puget Soimd Railway by a spur up Halfbreed Creek to the mine.

In October, 1908, the Roundup Coal Mining Company opened in sec. 23, T. 8 N., R. 25 E., a commercial mine consisting of a slope, with adequate equipment for mining, hoisting, and loading. This mine is connected with the main line of the Chicago, Milwaukee and Puget Sound Railway by a spur and is designed to supply coal for consumption of towns along the railway, the entire production of the Republic Coal Company being utilized by the railway company.

Local demands for coal in Roundup and other settlements along the Chicago, Milwaukee and Puget Sound Railway will increase as a result of the growth of manufacturing industries and gain in population.

7063**— BuU. 381—10 6

The Milk River Coal Field, Montana.

By Leon J. Peppebbebo.

Introduction.

Field work. — This paper is a preliminary statement" of the results of a detailed survey of a part of the Milk River coal field, Montana, made during the summer of 1908 by the writer with the assistance of V. H. Barnett. The object of this survey included not only the geologic and economic investigation of the area but primarily the classification of the public lands with respect to coal. Consequently the work was conducted with the view of ascertaining the extent of the coal areas and their relations to legal land subdivisions. In carrying on this work the geologic data were platted upon a base of recent topographic maps made by the United States Geological Survey on a scale of approximately 1 inch to the mile with a contour interval of 20 feet. This base covers the entire area examined, with the exception of a narrow strip about 1 J miles wide along the southern part of T. 32 N., Rs. 15 to 21 E., inclusive.

Previous reports. — Very little has been written concerning the geology or coal of this region. The most important work published by previous investigators is that of T. W. Stanton and J. B. Hatcher.* Their report, which deals with the geology and paleontology of the Judith River formation, contains a review and bibliography of publications relating to this formation in Montana and Canada. Brief mention of the coal of this field is made in a report by J. P. Rowe* and the field is referred to in several reports of the inspector of coal mines of the State of Montana and in the ''Mineral Resources of the United States."

The glacial geology of the region has been briefly discussed by F. H. H. Calhoun,* and papers describing the prominent features of

A detailed report is dow in the course of preparation, to be issued as a separate bulletin of the United States Geological Survey.

Geology and paleontology of the Judith River beds, with a chapter on fossil plants by F. H. Knowlton: Boll. U. & Oeol. Survey, No. 257, 190S.

e Montana coal and lignite deposits: Bull. Univ. Montana No. S7 (Oeol. series No. 2), 1906, pp. SIMO.

tf MlMral Resoorces U. 8. for 1907, pt 2, U. S. Oeol. Survey. 1906. pp. 14150.

eTiM Montana lobe of the Keewatin ioe sheet: PioT Paper U. 8. Oeol. Survey No. 50, 1906.

a2

Milk River Coal Field, Montana. 83

the Bearpaw Mountains with special reference to igneous rocks have been published by W. H. Weed and L. V. Pirsson."

Location and extent. — The part of the Milk River coal field herein described is located in Chouteau County in north-central Montana. The greater portion lies in the Milk River drainage basin, but it also includes a strip in the extreme southwest comer which drains into Missouri River. The area examined embraces Tps. 32 to 34 N., Rs. 12 to 24 E., inclusive, along Milk River and the main line of the Great Northern Railway, and an irregular tract from the north boundary of T. 31 N. to the south boundary of T. 26 N., Rs. 10 to 14 E., inclusive, along the Montana Central division of the Great Northern Railway. The area as described includes over 2,000 square miles, but only that part which contains coal of importance is shown on the accompanying map (PI. VI).

Topography And Geography.

The area under consideration is situated in the northwestern part of the Great Plains region. For the most part it is covered with a fair growth of grass and scattered patches of sagebrush. Trees are noticeably absent except along Milk River and its larger tributaries east of Havre, where cottonwood, willow, and underbrush grow close to the drainage ways. When viewed from the highlands the country has a rolling aspect, exhibiting no abrupt changes except where tributaries to the main river have eroded deep channels in passing from the higher land to the valley and where a few lava butter south and southwest of Havre stand out prominently in comparison to the surrounding flat, treeless plains. In the extreme northeastern portion of the area the bench land has an altitude of 3,220 feet while the lowest point in the southeast comer is 2,320 feet above sea level. The average elevation of the area examined is 2,600 to 2,800 feet.

Almost the entire region imder discussion is drained by Milk River, which enters the area in the northwest comer at an elevation of about 2,570 feet. It flows through a narrow, steep-walled valley in a southeasterly direction for about 14 miles and then makes an abrupt turn to the east and continues in this direction for about 24 miles. The course of the river from this point is almost due northeast for 4 miles, beyond which it flows in an east-southeast direction until it crosses the south boimdary of the area at an elevation of 2,320 feet above the sea. Within the area examined Milk River flows circuitously about 114 miles in a distance of about 70 miles, forming numerous oxbows, cut-off lakes, and wide migrating meanders on its way. It has a fall of 230 feet, or approximately 2 feet to the mile. The valley of Milk River in the western part of the field is narrow and

a Am. Jour. ScL, 4th aer., vol. 1, 1896, pp. 283-301; vol. 2, 1890, pp. 188-199.

84 Contbibutions To Economic Geology, 1908, Pabt Ii.

steep walled, some of the cliffs rising 200 feet above the water level. It has been pointed out by Calhoun" that Milk River now occupies the preglacial valley of the Missouri, which fonneriy flowed south of Havre and was joined by the preglacial Milk about 3 miles east of that city near Stringfellow's ranch. At this point the preglacial Missouri crossed the present course of Milk River in a northeasterly direction and the decrease in the width of the valley below Stringfellow's ranch is conspicuous, but at Yantic Milk River reenters the broad valley formerly occupied by the Missouri and follows the preglacial channel until it leaves the area under discussion. At Yantic the Milk River canyon, which has had an average width of less than a mile, spreads out abruptly to one 3 to 4 miles in width. The cliffs recede and become less abrupt, and the stream is small in comparison with the valley it occupies.

The tributaries of Milk River are for the most part intermittent streams, but the drainage ways contain local water pockets and a few springs which afford watering places for stock. As a rule this water is too alkaUne for domestic purposes. The bench land is studded with numerous small intermittent lakes which occupy shallow depressions in the glacial drift. The water in these lakes, especially in the smaller ones, contains salts leached, from the soil and is therefore alkaline.

The principal towns in the area are Havre, Chinook, Harlem, and Big Sandy. The first three are situated along the main line of the Great Northern Railway, which crosses the southern half of the field from east to west. Big Sandy is located in the southwestern part of the field, on the Montana Central division of the Great Northern Railway, which leaves the main line about 4 miles west of Havre and runs in a southwesterly direction to Great Falls and Helena.

Geology.

Stratigraphy.

The sedimentary rocks outcropping in the part of the Milk River coal field under discussion consist mainly of sandstone and shale which belong to the Montana group of the Cretaceous system with the exception of a small infaulted area of Tertiary rocks about 6i miles east of Big Sandy. These rocks are largely covered by glacial materials on the bench-land areas and by alluvial deposits in the larger valleys. In a few places they are cut by igneous intrusions or covered by lava flows.

a Op. dt., pp. 3839.

Milk Biveb Coal Field Montana.

ThQ following formations; which are given in ascending order, outcrop in this fidd: Eagle sandstone, Claggett formation, Judith River formation, Bearpaw shale, and Fort Union formation.

Straiigrapky of the Milk River coalfield, Montana.

System.

Tertiary. (Fault.)

Qroap or formation.

Fort UiiioD formation.

Thick- Bttsa.

Feet.

Bearpaw shale.

Jodltli River formatfon. 480

Claastt fonnatioD 350

Eale sandstone ' 250+

Description.

/Alluvial deposits. \Oiadal drift.

Massive gray to buff sandstone and thin of gray shale, vrith lignite beds.

Leaden-gray shale, with thin beds of sandstone and large concretions. Alternating beds of lightroolored sandstone,

shale, and lignita. Dark gray shales, with thin beds of ball

sandstone near top and bottom. Massive to calcareous white to creara-colored

sandstone, focally cross bedded: at top

dark-gray shale, with intercalated beds of

gray to buff sandstone.

Tjfpeb Oketagbou8 Rocks (Montana Group).

Eagle Sandstone.

The Eagle sandstone, which is the lowest formation in the Montana group, outcrops along Missouri River and several of its tributaries in the extreme southwestern portion of the field. The basal member of this formation is a massive, calcareous, white to cream-colored, persistent, usually hard, and locally cross-bedded sandstone about 100 feet thick. Wherever the base of the Eagle is exposed it constitutes a horizon marker that is easily recognized. In the top 30 feet of the sandstone are numerous concretionary hard lenses of sandstone, some of which are highly stained by iron. These harder parts resist the effect of weathering much better than the rest of the sandstone and stand out as prominent knobs or cap thin rounded or angular spires of the underlying softer material. In places the entire massive stratum forms a steep chfT several miles in length and about 100 feet in height.

The upper member of the Eagle sandstone, which has a thickness of about 150 feet, is easily separable from the lower by its marked lithologic and topographic differences. The sandstone strata in this part of the formation are thin and more friable than those in the lower member. Sandy shales and carbonaceous layers with streaks of coal predominate in the lower half, but the upper half is principally dark-gray shale with a few intercalated beds of gray to buff sandstone. The line between the two members of the Eagle is very pronounced. Overlying the massive white ledge of sandstone are a number of

86 Contributions To Economic Geology, 1908, Part Ii.

coaly beds and carbonaceous shales which give this zone a dark color. The upper member, being much softer than the lower member, weathers into long, rounded slopes. Coal beds 6 to 8 inches in thickness were observed, but the greater part of the carbonaceous matter consists of black shale interbedded with fine laminae of coal.

Claggbtt Pormation.

The Claggett formation, which consists largely of dark leadengray shales intercalated with thin beds of buff sandstone near the top and bottom, overlies the Eagle conformably. It is very similar lithologically to the Bearpaw shale, from which, without the aid of stratigraphic or paleontologic evidence, it is often distinguished with difficulty.

Gypsum flakes or crystals are scattered throughout this soft shale. Hard concretions of different sizes up to several feet in diameter are numerous, especially near the top. The concretions are calcareous and are usually traversed in all directions by cracks filled with ambercolored calcite or gypsum crystals. Invertebrates are found in the shale but more often in the calcareous concretions ; however, they are not so abundant in this formation as in the Bearpaw shale. (See p. 84.) No coal occurs in this formation, but some thin carbonaceous shale was observed near the top. The Claggett in this field has an estimated thickness of 350 feet.

Judith River Formation.

The Judith River formation overlies the Claggett conformably and is composed of alternating light-colored beds of sandstone and shale. It is almost entirely a fresh-water formation but some brackish-water beds are included at the top in the transition zone between the Judith River and the marine Bearpaw shale and at the base in the transition from the marine Claggett to the fresh-water Judith River formation. There is no persistent member in the entire formation which can be followed for any great distance. The ash-colored sandstone is locally cross-bedded and contains iron-stained concretionary bands. In some places the sandstone is hard and massive; in others it is soft and friable. The shales, sandstones, and coals of this formation are very lenticular and it is common to find a massive sandstone grading into a soft shale or a sandstone or shale grading into a carbonaceous shale or thin coal bed within a comparatively short distance horizontally. In the same manner a coal bed which consists of clean coal of workable thickness may pinch out altogether and be replaced by a sandstone at the next exposure half a mile away. A coal bed from 1 to 12 inches in thickness was observed in the base of the Judith River, but the coals of workable thickness occur within the upper 150 feet of the formation.

Milk Biver Coal Field, Montana. 87

This fonnation outcrops extensively along Milk River northwest of Havre and near the mouth of Boxelder Creek in T. 32 N., R. 17 E., where intense erosion has carved it into typical badland forms. It has a total thickness of about 480 feet.

Bbarpaw Shale.

The Bearpaw shale overlies the Judith River formation conformably and consists of dark leaden-gray shale containing thin beds of sandstone and large concretions, many of which are highly fossilifer- .ous. These round and oval bodies are fissured and the cracks are usually occupied by crystalline calcite. Selenite or gypsum flakes are scattered throughout the formation.

As previously stated, the Bearpaw and Claggett are very similar lithologically. Both are leaden gray in color, both contain similar concretionary masses and thin beds of sandstone and both weather into long, roimded slopes and form barren patches of loose weathered shale. The Bearpaw, which is represented by observed outcrops 80 to 100 feet in thickness in this field, has a known thickness of 350 to 900 feet in other parts of Montana.

Tertiary System (Port Union Formation).

Abundant fossil plants which are, according to F. H. Knowlton, of Fort Union age, were collected in sec. 18, T. 28 N., R. 14 E., about miles east of Big Sandy. These leaves occur above and below the coal beds in this district. The Fort Union outcrops in the westem foothills of the Bearpaw Mountains, where it covers only a small area. From the few outcrops noted it was impossible to determine which part of the formation is present in this field, but it may possibly correspond to the upper yellow beds of the formation as developed in northeastern Montana and northwestern North Dakota.

Lithologically the Fort Union is notably diflFerent from the Judith River formation; it consists largely of massive strata of gray to buff sandstone, which are very persistent, and of thin beds of gray shale. These strata contain several beds of good coal which are discussed elsewhere in this paper. The position of this formation in the geologic column is several himdred feet above the Cretaceous formations already described, and its occurrence in this district is due to a fault having an estimated throw of about 2,000 feet.

Glacial And Alluvial Deposits.

Among the features which should be fully described in any complete account of the region are several types of glacial and alluvial deposits, such as ground and recessional moraines, kames, eskers, drift, till, and river and lake deposits, which cover the greater part of the area. These features of recent glaciation and erosion can be only mentioned here.

88 Contributions To Economic Geology, 1908, Pabt U.

Igneous Rocks.

In the area under consideration igneous rocks are comparatively rare, but a few prominent buttes are present in the vicinity of Havre and in the southwestern part of the field. The igneous rocks, which are of post-Eocene age, include both extrusive and intrusive types and have had little or no effect on the coal.

Structure.

As the area is largely covered by glacial and alluvial deposits and continuous exposures for great distances are lacking, the structure is very obscure. Except in a few places where the glacial cover is extremely thin, the only outcrops present in the field are along the lines of drainage where erosion has removed the glacial mantle. At these places the sedimentary rocks outcrop in small patches or long, narrow strips on either side of the coul6es and along well-drained slopes. These rocks, which were originally approximately horizontal, have been subsequently disturbed by numerous faults and folds, which make the working out of the stratigraphy rather difficult. A vivid idea of the abundance of these disturbances is given by Ilayden, as follows:

The meet remarkable feature of this basin is the wonderful disturbance of the strata. So much are the beds disturbed and blended together by forces acting from beneath that it seems almost hopeless to obtain a section showing with perfect accuracy the order of superposition of the different strata.

The faults of the Milk River field are too numerous to be described individually. They are in general closely associated with folds and for the most part are of the thrust type, although a few normal or tension faults were observed. The faulting is best developed in the regions where the folding has been greatest. The larger thrust faults were probably developed at about the same time as the folds with which they are associated, and with one or two exceptions they are in a general way parallel to the axis of the Bearpaw Mountains.

The disturbances mentioned have caused lateral and vertical offsets of the coal beds, in many places tilting them to high angles.

THE COAIi.

GENERAL STATEliENT.

All the coals in the Milk River field, so far as studied, may be classed as a fair grade of subbituminous coal (''black lignite"). Most of the coal beds are lenticular in shape, showing a variation in thickness from a fraction of an inch to 9 feet at different points on the outcrop. These beds are noticeably thinner and of a lower

aHayden, F. V., Proc. Acad. Nat. Sci. Philadelphia, 1857, p. 116.

Milk Biver Coal Field, Montana. 89

grade in the eastern part of the field than in the western part, so that beds of considerable thickness and good quality in the vicinity of Havre contain little or no coal near Harlem. Generally there is one bed, in some localities two, and in others four beds, all of workable thickness. The greater part of the coal of workable , thickness occurs in the upper part of the Judith River formation (Upper Cretaceous), from 10 to 150 feet below the base of the Bearpaw shale, the only exception being the coal east of Big Sandy, which is of Fort Union (Tertiary) age.

On accoimt of the small number of mines and prospects in the area it was necessary to study the coal largely from the weathered outcrops of the bds and from the data thus obtained to infer the character of the coal. The method employed in pursuing this study may be outlined briefly as follows. A careful search was made in coulees and ravines over the whole area for outcrops of coal beds. All coals thus found were traced by foot traverse imtil they pinched out, were covered by glacial or alluvial material, or were cut out by faults. All mines and prospects visited and all coal outcrops traversed were platted upon a topographic base prepared by the United States Geological Survey and all the coal beds were measured. Samples for chemical analysis were taken from the principal beds at the mines and prospects throughout the area. The examination showed that the topographic maps were well tied to the land surveys, and the section comers were so well marked that no diflBculty was experienced in locating a comer when it was desired to tie a coal crop or prospect to a known point. The extensive glacial and alluvial covering in this field or the slumping of talus obscures the outcrop of coal over large areas, making the continuous tracing of coal beds or formation boundaries impossible.

In many places the coal beds and carbonaceous shale have been burned along the outcrop and the adjacent rocks have been baked to a red material resembling brick or tile. Prospects driven through the burned areas where the covering is from 20 to 50 feet thick demonstrated that it extends from 30 to 70 feet from the present outcrop of the hardened clinker and ash, and that the good coal bed continues behind the burned crops. The map (PI. VI) shows the location of the coal zone, mines, and prospects with relation to the section comers, and such other geologic data relating to the coal as the scale of publication permits.

Dbtailrd Dsscriptions.

For convenience the parts of the Milk River coal field with which the present report is concerned will be discussed as separate units termed the Havre, Chinook, Harlem, and Big Sandy districts. The

90 Contributions To Economic Geology, 1908, Pabt H.

boundaries of these districts have been arbitrarily chosen with reference only to the towns near which the greatest amount of mining is being carried on and from which coal shipments can be made.

Havre District.

The Havre district is the best known in the Milk River field, on account of the local demand for the fuel and the fact that the largest coal mine in the area is located within its borders. This district as here treated embraces all of Tps. 32 to 34 N., Rs. 14 to 17 E., inclusive, and the northern tier of sections of T. 31 N., R. 17 E. Future work in this field will extend the boundaries of the Havre district both to the north and south of the area herein described. The coal of the district is as accessibly as any other in the region and is easUy reached by wagon roads which traverse the area in all directions. The sections given in the following pages show the thickness and contents of a few of the principal coal beds exposed at various locaUties throughout the field.

Locality The following section was measured in a prospect opened by Mr. Co wen in 1898 and worked during the winter of 1907 by Mr. Schean :

Section of coal bed in prospect in SE. i NE. i sec. 28, T. 33 N., R. U E. (No. J).

Ft. In.

Shale, carbonaceous 2 3

Coal 3

Bone and clay 1 5

Coal 4

Bone 3

Total coal 3 4

This bed was sampled at the breast of the workings about 75 feet from the mouth of the entry, where the coal showed little or no effect of slacking. The main coal has a bright black luster, is solid, and has a semiconchoidal fracture. On exposure to the air it loses moisture rapidly and checks or disintegrates into small irregular bits. The prospect is located about 30 feet southeast of a small fault which cuts the coal out to the northwest. Another small fault about 60 feet southeast of the opening limits the outcrop of the bed in that direction.

At the head of Supenau Coulee, in sec. 1, T. 33 N., R. 14 E., the coal zone of the Judith River formation is again exposeil. Here the beds have a low dip to the northeast, which shows that the area to the north is underlain by the coal bed, while that south of the coal crop in the northern part of sec. 12, T. 33 N., R. 14 E., is probably not underlain by coal. On account of poor exposures no measurements were made of the coal at this place.

a Numbers like this correspond to those on PI. VI.

Milk Biyeb Coal Field Montana. 91

Locality 2: The following section was measured on the south side of Redrock Coulee, where a bed of coal which lies almost flat and under thin cover outcrops for a short distance. This coal is badly weathered but shows good cubical joints, indicating that it would probably prove to be of good quality. Redrock Coulee derives its name from the red rocks along the burned coal crops in T. 33 N., R. 17 E.

Section of rocks exposed in SE, J sec. W, T. S4 N., R. 15 E, (No. 2).

Ft. in.

Glacial deposits 17

Shale, carbonaceous 2

Bone 1

2 6

Locality 3: The following section was measured near an abandoned prospect in sec. 7, T. 33 N., R. 15 E. The bed dips slightly to the northeast and probably underlies the greater part of the area between this point and locality 2.

Section of coal in SE. J sec. 7, T. SS N., R. U E. (No. S).

Ft. In.

Glacial drift 10

Coal 1 4

Shale, carbonaceous 1

Coal 1 6

Bone 8

Bone with coaly streaks 2 6

Total coal 2 10

Locality 4: The character of the bed in the southeastern part of T. 33 N., R. 15 E., is represented in the following section, which was measured at an abandoned prospect in sec. 25 :

Section of coal bed at prospect in NW. J sec. 25, T. SS N., R. 15 E. (No. 4).

Shale, carbonaceous. Ft. in.

Bone 1 6

Shale, carbonaceous 3

Coal, clean 3

Bone 3

Shale, soft gray 5

Coal, rather bony 1 4

Bone.

Total coal 4 4

This zone continues in a southeast direction under the glacial drift and is next exposed in sec. 31, T. 33 N., R. 16 E., south of the Havre Fuel Company's mine. It will be described xmder locality 8.

Locality 5: The following section was measured in a prospect located in the southwestern pait of T. 33 N., R. 15 E., where the coal

92 Contributions To Economic Oeoloot; 1908, Part Ii.

outcrops south of a thrust fault. This prospect, which was opened by H. Barrott, is worked by the room and pillar method. The main entry is about 250 feet long and follows the dip of the bed, which is about NE. at this place.

Section at BcmrotVs prospect in SW. sec, 29, T. SS N., R. 15 E. {No. 5,)

Clay, shaly. Ft. in.

Shale, carbonaceous 2 6

Coal 8

Bone 4

Shale, carbonaceous 4

Coal 2

Bone 7

Coal 3 3

Total coal 4 1

The sample of coal which was taken from the 3-foot 3-inch bench of the above bed gave a calorific value of 8,944 British thermal units in the air-dried state.

Locality 6 : The coal zone of the Judith River formation outcrops at various places in the bed of Coal Creek in the northern tier of sections of T. 33 N., R. 16 E. Here the beds, which dip about 3® NE., lie under very little cover and are badly weathered along the outcrop. The best exposure is at locality 6, in the SE. J sec. 2, on the south bank of the creek. The following section represents the character of strata exposed at this point:

Section of rocks exposed in SE. J sec. 2, T. SS N., R. 16 E. (No. 6).

Ft. in.

Glacial drift 4

Sandstone, clayey soft 3

Shale, carbonaceous 2

Bone 4

Shale, sandy, carbonaceous 3 6

Coal 5

Bone f 7

Coal 1 9

Clay, sandy, white 2

Coal 1 6

Shale, sandy, carbonaceous 1 8

Shale, drab 5

Coal 11

Bone 4

Coal 1 2

Bone, with coaly streaks 1 9

Bone 4

Coal 11

Bone 5

Shale, black, carbonaceous.

Total coel 6 8

Milk Biveb Coal Field, Montana. 93

Althou the coal is badly weathered, it has well-developed culMeal joints eyen at the surface, and by very little digging fresh coal of bright luster was uncovered, indicating that good coal exists within easy reach of the surface or within a short distance from the present outcrop. The coal extends beneath the glacial drift to the south, where it outcrops along the north side of a small coulee in sees. 28 and 29, T. 33 N., R. 16 E. At this place the coal contains numerous partings of bone and Ues nearly flat imder thin cover. Prospects have been driven at the head of the coulee in the N. sec. 29, where the thickest bed contains three benches of coal 14, 16, and 17 inches thick, separated by 6 and 8 inches of bone. It is reported that these prospects were abandoned on account of the large amount of bone which could not be economically separated from the coal. From this point the bed swings to the southeast and then to the west around the head of a coul6e at the Alcott and Gussenhoven prospects.

LocaUty 7: The following section down the slope of the Alcott prospect shows the coal content of the beds measured :

Section down the slope of the AlcoU prospect in NW. SW. sec. 29, T. SS N., R, 16 E.

(No. 7). Glacial drift. Ft. in.

Shale, carbonaceous 8

Coal 4

Shale, carbonaceous 9

Shale, sandy 7 10

Shale, brown, carbonaceous I4

Shale, black, carbonaceous i

Bone, with coaly layers 4

Coal 10

Bone 3

Shale, with thin coaly layers 7

Shale, gray 3

Shale, carbonaceous 3

Coal 1 2

Bone, with thin coaly layers 2

Shale, carbonaceous 5i

Clay, ash-colored 2 10

Shale, carbonaceous 3

Coal, with thin bone seams 5

Bone J

Coal 6

Bone H

Coal 8

Bone 10

Coal 2 2i

Bone, with thin coaly layers 1 2

Clay 4

Bone 4i

Bone, with thin coaly layers 10

Total coal 6 li

94 Contributions To Economic Geology, 1908, Part Ii.

The lower 5i feet of the above section is being worked in this prospect. The 2-foot 2J-inch bench is clean coal of bright luster, with well-developed cubical joints and a calorific value of 9,729 British thermal units on the air-dried sample. The area between the Alcott prospect and the Havre Fuel Company's mine is imderlain by this bed.

LocaUty 8: The following sections were measured at different points in the workings of the Havre Fuel Company's mine in the NW. sec. 31, T. 33 N., R. 16 E., and show the variations in the same bed withm a comparatively short distance:

Sections of coal bed in Havre Fuel Company s mine, NW. J sec. SI, T. SS N., R. 16 E,

(No. 8).

Ft. in.

Roof, coal 1±

Coal 9

Bone 5

Coal 1 5

Bone 2

Coal 11

Bone 10

Coal 8-10

Floor, shale, black, carbonaceous.

Total coal 4 9 to 4 11

Ft. In.

Roof, shale, with thin coaly layers 1 4

Bone 2

Coal 9

Bone, with thin coaly layers 10

Bone 6

Coal 2 6

Bone 6

Coal 4-8

Floor, shale, carbonaceous.

Totalcoal 3 7 to 3 11

A number of other sections measured in this mine show the coal and bone to be variable throughout the workings. In several places the bed consists almost entirely of bone with thin seams of coal; in others the clean coal predominates and is from 25 to 34 inches thick. The mine is the largest in the Milk River field, having imderground workings about 2 miles long, as shown on the mine maps of the company. The mine workings lie under about 72 feet of cover, and according to information received from tlie foreman there are two coal beds above the one that is now being worked; one, about 10 feet above the workings, has a thickness of 2 to 2i feet, and the other, about 25 feet above the workings, has a thickness of 8 to 10 inches. Both beds probably contain bony and shaly streaks.

Milk River Coal Field, Montana. 95

From the data given under localities 2, 3, 4, 6, 7, and 8 it is evident that the area between these points is probably underlain by beds of coal, some of which are possibly of workable thickness and fair quality- Locality 9: The dip of the coal bed in the prospect where the following section was measured is about 10 S. 40° W. This high dip is due to several small faults in the immediate vicinity.

Section of coal bed in a prospect in the SW. i sec. 29 y T. St N., R. 16 E. (No. 9).

Roof, shale, gniy* Ft. in.

Cool 1 10

Bone, with coaly streaks 2 4

Coal 2 2

Floor shale.

Total coal 4

Locality 10: The following section was measured in an abandoned prospect northwest of Brown's prospect, in sec. 21, T. 32 N., R. 17 E.

Section of coal hedin old prospect in the SE. i NE. i sec. fi, T. Si N., R. 17 E. {No. 10).

Shale, buff, sandy. Ft in.

Coal, clean 1 2

Bone 3

Coal, clean 3 4

Bone 2

Coal, clean 5

Total coal 4 11

At one place in this prospect 45 inches of clean coal was measured. At the Brown prospect, less than one-quarter mile southeast of locality 10, this bed of coal contains numerous partings of bone, showing that the coal is not persistently clean for even short distances along the outcrop.

Coal belonging to the same zone outcrops at various places along Boxelder Creek and at the heads of coulees in sees. 1, 9, 10, and 11, T. 32 N., R. 17 E. The section of the bed is, however, very changeable. The beds in the northern part of the township are thinner and contain more partings of bone than those at locality 10, and the same may be said of the area southeast of th point where the section was measured.

Locality 1 1 : The following section was measured in the Clack prospect, in the NE. sec. 5, T. 31 N., R. 17 E.

Section of coal bed in Clack prospect, NE. sec. 5, T. SI iV., R. 17 E. (No. 11),

Ft. in.

Roof, coal 1±

r,oal 2 8

Bone 1

Coal 1 C)

Floor, bone.

Total coal 4 2

96 Contributions To Economic Geology, 1908, Past Ii.

In working the above bed the 1-foot bone is mined out, then the coal is loosened by firing shots first in the bottom and then in the top bench of coal. In this way large lumps are obtained. The coal is of gbod quality and represents the same zone as that exposed in the Staton mine about 1 mile east of this point.

Locality 12: The following section measured in the Staton mine shows the character of the bed, which probably underlies the larger part of the southern tier of sections in T. 32 N., R. 17 E., and the two northern tiers of sections in T. 31 N., R. 17 E.

Section of Staton coal bed in NE. J sec, 4, T. SI N., R. 17 E. (No. It).

Ft. In.

Roof, coal 1±

Coal 3 1

Bone 10

Coal 1 101

Total coal 4 llj

The coal zone outcropping in Tps. 33 and 34 N., R. 17 E., consists of very poor carbonaceous shale and bone containing many thin, coaly layers. In several places this bituminous shale and bone has burned along the outcrop. No coals of notable thickness were observed in this part of the field.

Chinook District.

The Chinook district joins the Havre district on the east and embraces Tps. 32 to 34 N., Rs. 18 to 20 E., inclusive. Only a part of the district has been examined, and further field work will extend the boundaries to the north and south. The coal is easily reached by wagon roads leading in all directions across the bench land from the towns and ranches.

Locality 13: The following section was measured on the West Fork of Milk River, 1 mile northwest of Reser's ranch.

Section in the NW. sec. 2, T. 34 N., R. 18 E. (No. IS),

Shalo, brown, carbonaceous. Ft. in.

Coal, with thin, bony layers 3 6

Shale, brown, carbonaceous 1 4

Bone, with thin, coaly layers 2 8

Coal 3

Bone, with thin, coaly layers 1 5

Covered.

Total coal 3 9

This bed is exposed on the north side of West Fork of Milk River south of a fault line. The dip at the outcrop is about 60 S., decreasing rapidly away from the disturbed zone. The Judith River forma-

Milk River Coal Field, Montana. 97

tion is overlain by the Bearpaw shale south of the outcrop, giving the coal a good cover. That the eastern part of T. 34 N., R. 18 E., is underlain by workable beds is indicated by outcrops of the Bearpaw shale, which overlies coal at localities 13 and 14. In the southern part of the township the coal is not well developed. Here the beds resemble those in T. 33 N., R. 17 E., of the Havre district and consist mostly of carbonaceous shale and bone with thin coal seams.

Locality 14: The following section shows the character of the coal exposed in the McLelland prospect:

Section at the McLelland prospect, NW. sec. 12, T. S3 iV., R. 18 E. (No. 14).

Ft. in.

Bone, with thin coal lewis(\s 1

Goal, with thin, bony streaks 2 4

Bone 4

Coal 6

Bone 5

Total coal, about 2 10

From the McLelland prospect the coal is traceable southeastward for about miles, to a point where it again disappears beneath the glacial drift.

The greater part of T. 33 N., R. 18 E., is occupied by valley wash, and as the coal-bearing formation has been eroded the land is important only for agricultural purposes. In the northwestern part of T. 32 X., R. 18 E., the coal zone outcrops along a coul6e, but no beds of importance were observed. The zone is again exposed along Clear Creek in the same township. The thickest coal measured along this creek is 2 feet 8 inches thick.

Locality 15: The following section was measured at the Bums prospect, about a mile east of Clear Creek, and shows the character of the coal which probably underlies the area between the two places.

Section at Burns prospect, NW. J sec. 11, T. S2 N, R. 18 E. (No. 15).

Glacial drift. Ft. in.

Shale, carbonaceous 1

Coal 4

Shale, sandy, carbonaceous 3

Shale, carbonaceous 3 6

Bone 4

Coal 3

Total coal 3 4

The structure in T. 34 N., R. 10 E., is complicated by numerous faults, large and small, and as the coal crops can not bo traced for any great distance, the sections given represent purely local conditions.

7963*'— Bull. 381—10 7

98 Contributions To Economic Geology, 1908, Part Ii.

However, it is reasonable to suppose that wherever the Bearpaw outcrops in this township the area is underlain by workable beds similar to those given under localities 16 and 17.

Locality 16: The following section was measured on the south bank of the West Fork of Milk River at the Leabo prospect, in sec. 29, T. 34 N., R. 19 E.

Section at Leabo prospect, SW, sec. ;?9, T. S4 N., R. 19 E. (No. 16).

Ft. In.

Glacial drift 10

Shale, carbonaceous 3

Coal, rather bony 1 6

Shale, carbonaceous 1 4

Shale, sandy 9

Shale and thin sandstone 16

Coal, rather bony 3 6

Clay, sandy 5

Coal 8

Bono 1

Coal, same as in Leabo prospect 3 4

Covered 10

Coal exposed in bed of West Fork, partly covered by water. . 4

Total coal about 13

The outcrop of this coal bed continues southeastward and then westward beneath the glacial cover and connects with the bed exposed at the Milk River Coal Company's mine (locality 18).

Locality 17: The character of the coal underlying the eastern half of T. 34 N., R. 19 E., is shown in the following section:

Section of rocks near center of sec, 23, T. S4 N., R. 19 E. {No. 17).

Ft. In.

Glacial drift 5

Shale, carbonaceous 1

Coal 3±

Shale, carbonaceous 2

Coal 3±

Shale 6

Shale with coaly bands 7

Clay, Handy 2

Shale, carbonaceous 2

Coal with thin bony streaks 1 3

Shale, carbonaceous 2

Covered.

Total ('oal 7 3±

Coal zone.imoe, Mnd prospect

Undifferentiated glacial drift

IflLK BIVEB COAL FIELD, MONTANA. 99

Locality 18: The following section measured in the Milk River Coal Company's mine shows the character of the bed worked at this place. Besides the bed worked by the company there are two beds containing from to 4 feet of coal and bone in the same locality. The bone content is variable.

Section of coal bed in Milk River Coal Companys mirier NW. J NW. sec. 18, T. SS N.,

R. 19 E. {No. 18).

Bone, with coal streaks: Ft. In.

Coal 1

Clay 2

Coal 1 7

Bone 1 2

Coal 2 6

Shale, carbonaceous.

Total coal 5 1

The coal outcropping in the northeast quarter of T. 33 N., R. 19 E., has been disturbed by faults. In many places it has burned out. No good exposures were discovered, but there are probably coal beds from 2 to 3 feet thick.

Locality 19: The following section measured at the Tumbler prospect shows the character of the coal outcropping in T. 33 N., R. 19 E. The beds in this township have been distorted in many places by aults, consequently it is impossible to trace a single bed for any great distance, even where the rocks are well exposed.

Section of coal bed in the Tumbler prospect, NW. i NW. i sec. S)*, T. .ii N., R. 19 E,

(No. 19).

Ft. In.

Coal 2 4

Bone li

Coal 7i

Bone 3

Coal 2

The coal beds outcropping in T. 34 N., R. 20 E., are unimportant and may be dismissed without further comment. It should be borne in mind, however, that workable beds, which do not outcrop within the township, may underlie it.

Locality 20: In the NE. SW. sec. 10, T. 33 N., R. 20 E., a coal bed is brought to the surface by a fault which has a northwestsoutheast trend. A small prospect known as the Matheson mine is located on this coal on the west side of Coal Coulee southwest of the fault line. The following section was measured at the mouth of this prospect.

This bench has betn unintentionally omitted in the graphic section (No. 18, PI. VI)

100 Contributions To Economic Geology, 1908, Part H.

Section at Matheson prospect, NE. i SW. i sec. 10, T,SS N., R, 20 E. {No. 20).

Ft, in.

Coal 1 2

Shale, carbonaceous 4

Shale, sandy carbonaceous 1 2

Coal 2

Bone 4

Coal 1

Bone 6

Clay, sandy 1

Coal 1

Bone 1

Shale, carbonaceous 2

Total coal 5 2

This is the only important bed which outcrops in the township. The coal bed mapped in the southern part ot the township consists of carbonaceous shale and a thin bed of dirty coal 1 to feet in thickness.

A dirty bed of coal corresponding to the one just described , but having a thickness of about 2 feet 9 inches, outcrops in the eastern part of T. 32 N., R. 20 E. This bed contains little clean coal, but consists of alternating layers of bone, carbonaceous shale and mineral charcoal, and thin coaly layers. The cover is thin, and the bed is badly weathered along the outcrop.

Locality 21: The Judith River formation outcrops in the southwestern part of T. 32 N., R. 20 E., and is overlain by the Bearpaw shale. The strata show evidence of faults. The only coal of importance within the township outerops along the Sixmile Coulee. The following section measured in the Kerr mine shows the character of this bed:

Section in Kerr's mineN W. SW. J sec. SO, T. SJ N., R. 20 E. (No. 21).

Ft. In.

Roof, shale, black, carbonaceous.

Coal 6

Coal, bony 5

Coal, good 2 5

Floor, bone.

Total coal 2 11

From the foregoing discussion it is evident that the coal zone, which contains good workable coals in the Havre district and the western two-thirds of the Chinook district, becomes poorer as a source of thick coals toward the east. The beds in the eastern part of the Chinook district are thinner, contain more bone, and are less persistent than those in the western part of the area discussed.

Milk Biveb Coal Field, Montana. 101

Harlem District.

The Harlem district is the least importaDt ia the part of the Milk River field under consideration. It joins the Qkinook district on the east and embraces Tps. 32 to 34 N., Rs. 21 to 23 E./ inclusive. As in the Havre and Chinook districts, only a part of theHarlem district was examined during the summer of 1908, and future field work will extend the boundaries to the north and south of the area deficfibed here. The coals gradually become thinner and of poorer quality from west to east in this district, and with few exceptions the beds consist largely of bony coal under thin cover and consequently of low value as a fuel. Owing to the scarcity of wood in the district it has been necessary to work beds of coal which, in other localities, would be considered almost worthless at the present time. The coal in the area is easily accessible by wagon roads from Harlem and the ranches in the district.

The thickest coal observed in T. 34 N., R. 21 E., is only 8 inches thick, consequently the coals outcropping in this township may be dismissed without further comment.

Locality 22: At a small prospect in the NE. sec. 26, T. 33 N., R. 21 E., the following section was measured. The bed at this locality has a dip' of 40° N. 60° E., due to a northwest-southeast fault.

Section of coal bed at prospect in NE. i sec. 26, T. S3 N., R. 21 E. (No. 22).

Ft. in.

Shale, brown carbonaceous 4

Coal, with numerous partings of sandstone and bone 3 6

Shale, carbonaceous with thin coaly layers.

The coal of the above bed is pockety; in some places the clean coal is over a foot in thickness but only for short distances, making it necessary to remove large quantities of rock to procure a small amount of good coal.

Locality 23 : The following section measured in unsurveyed sec. 9, T. 33 N., R. 22 E., at an abandoned prospect, shows the character of the coal along Thirtymile Creek:

Section at prospect in SW. sec. 9, T. S3 N., R. 22 E. (No. 23),

Ft. In.

Bearpaw shale 68±

Sandstone, soft, gray 20

Shale 10

Shale, sandy 3±

Coal 1 1

Bone 5i

Coal 1

Bone.

Total coal 2 1

102 CONTRIBUTIONS TO ECONOMIC OEOLOGY, 1908, PAKT n.

A sample taken from thb.betze a. calorific value of 8,568 British thermal units on the air-'dnetl coal, showing that the fuel is of low grade. However, part-..th'is low efficiency is due to the lai amount of ash caused by th'e'h.uinerous bony layers in the bed.

The strata axp'oaed along Thirtymile Creek have been disturbed by faults, making mining on the east side rather uncertain. The dips op ihfi west side are more constant and the coal is under thicker covei.V overlain by the Bearpaw shale.

ctial bed containing many partings and having a thickness of itbout 2 feet 9 inches has been prospected in the NW. i sec. 27, T. 33N., 'R. 22 E., and a bed of similar content was worked in the SE. sec. 30, T. 32 N., R. 22 E., during the winter of 1907-8. Coal from the lastnamed prospect sold for $7.50 a ton at Harlem, a distance of about 8 miles. From this statement it is evident that these towgrade coals have some value at the present time, especially durin;; severe winters.

Bio Sandy Distbict.

The sketch map {fig. 2) shows the location of the two principal mines in the Big Sandy district. They are situated in sec. 18,

f

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L,

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(

FiauHR 2.— Sketch map gf Big Band; district, Ullk REver nl field, Uentaoa.

T. 28 N., R. 14 E., about 6i miles east by a httle north of the town of Big Sandy, and are easily reached by wagon road from the town and ranches in the vicinity. These mines wore visited at the close of the field season of 1908, when the coal beds were measured and sampled. As no detailed mapping of formations of coal beds was attempted at that time, the boundaries of the district were not determined. As previously stated, the coals of this area are of Fort Union (Tertiary) age and consequently are younger than those of the Judith Iliver formation already described, which they overlie stratigraphic ally.

Icilk Biveb Coal Field, Montana. 103

The following section shows the character of the beds exposed at the Mackton Coal Company's mine:

Section at the MackUm Coal Company's mine, NW. \SW.\8ec. 18, T.t8 N,, R. 14E,

Sandstone. Ft. in.

Shale, sandy 2

Coal 4

Sandstone, buff, massive, intercalated with sandy gray shale.

Shale, carbonaceous 1

Coal 2 5J

Bone, variable 2

Coal 1 3

Bone 7

Coal 6

Bone 4

Coal 3 11

Clay, gray.

Totalcoal 12 li

The following section was measured in the NW. SE. sec. 18, T. 28 N., R. 14 E., in the Mack mine. The bed is probably the same as the upper bed given in the preceding section.

Section of coal bed in Mack mine, NW. SE. sec. 18, T. 28 N., R. U E.

Ft. In.

Clay shale, gray 1 8

Shale, carbonaceous 2

Bone, variable 4

Coal 5

Bone with thin coaly streaks 2 4

Coal 4 6

Clay.

Totalcoal 4 11

At the Mackton Coal Company's mine the strata dip about 40° E., indicating a north-south fault between this place and the Mack min, where the strata he practically flat. In the NE.i sec. 18, T. 28 N., R. 14 E., a coal bed outcrops along a coulee and has been prospected in several places. The strata at this place also show evidence of faults. The Judith River formation in the vicinity of Big Sandy contains several very thin coals, but no bed of workable thickness was observed in this formation within the Big Sandy district.

Character Of The Coal. Physical Properties.

In studying the coals of the Milk River field an attempt was made to gather as many facts as possible concerning their physical properties, and the principal characteristics observed may be briefly summed up. The coal of the Havre, Chinook, and Harlem districts is in general pitch black to brownish black in color, the streak Ls dark brown the

104 Contributions To Economic Geology, 1908, Part H.

luster bright and sometimes waxy. Two systems of joints are usually present and the coal commonly splits also along the bedding planes. The fracture of the solid coal is §emiconchoidal or irregular. Fresh samples are usually brittle, but sometimes tough. The texture varies from dense to woody. Thin incrustations of gypsum flakes in the form of selenite crystals occur between the joint and bedding planes, especially on the weathered outcrop. Some mineral charcoal, fossil resin, and, rarely, iron pyrites were observed.

The coal of the Big Sandy district is hard and brittle. Its fracture is principally conchoidal. It has a bright black luster and two systems of joint planes, one of which is better developed than the other. These beds are more regular than the other coals of the Milk River field; that is, in the small area examined the sandstone, shale, and coal beds seem in general to be persistent rather than lenticular.

Chemical Character.

The composition of the coal of the Milk River field is shown by the following analyses: The samples from which these analyses were made were collected in conformity with the regulations of the United States Geological Survey and the chemical work was done under the direction of F. M. Stanton at the Pittsburg laboratory.

Analyses of coal samples from the Milk River field Montana.

Location

Ilavre district.

Laboratory sample No.

Sample as received:

[Moisture

Volatile matter

Fixed carbon

\Sulphur

H ydrogen

Carbon

Nitrogen

Calories

British thermal units

Lossof moisture on air drying.

Air-dried sample:

Moisture

Volatile matter

Fixed carbon

/Ash

\Sulphur

Hydrogen

Carbon

Nitrogen

Calories

British thermal units

NE. i sec. 28, T.33N., K. 14 E.

G649

8,244

5,258

SW. J sec. 29,

NE. i sec. 26,

sec. 29,

T.33N.,;T.33N..;T..'0N R. 15E.IR. 15E.R. Ifi E

NW. i sec. 31, T.33N., R. 16 E.

8,417

4,969 8,944

5,444 9,799

21). 58 10. Xj

4,540

My. 39

5,405 9,729

SE. J sec. 30, T.32N., R. 16E.

.(iO

4,563 8,213

5,400 9,720

4,388 7,898

16.00 ' 15.50 ; 16.30

9,437

E. j sec. 21, T.32N., R. 17 E.

7,475

Ne. J

T.31 N., R. 17 E.

8.(i53

&19

4,607 8,293

5,370 9,600

Ne. J

Bcc. 4,

T.31 N., R. 17 E.

&74

10,163

Milk Biveb Coal Fieu), Montana.

AndlyteM of coal samples/rom the Milk River field, Montana — Continued.

Location

Laboratory sample No.

Chinook district

p

Sample as received:

Volatile matter

Fixed carbon

JAsh

Hydrogen

1 Carbon Nitrogen Oxyien

Calories

British thermal units.

Loss of moisture on air drying.

Air-dried sample:

Moisture

Volatile matter

Fixed carbon

Hydrogen

2' Caroon

Calories

British thermal units.

8W.J

sec 29,

T.34N.,

R. 19 E.

Nw.J

sec. 18,

T.33N.,

R.19E.

G.90

4,685 -8,433

NW. J sec. 32, T.32N., R. 19 E.

2t'>.59

4,808

8W.J

sec. 30,

T.32N.,

R.20E.

8W. J

sec. 10,

T.33N.,

R.20E.

7,798

6,755

10,350

9,821

9,583

5,090 9,162

Uarlem district.

SW. i

T.33N., R.22E.

3,841

4,760

8,568

Big Sandy d&trict

Sw. J Se.

SOC J Of SOC'

T.28N., T.28N., R.14E. R.14E.

.18,

9,598

9,938

6,642

10,156

10,626

A study of the analyses of coals from the Havre, Chinook, and Harlem districts shows that the Judith River coals of this field are comparatively low in sulphur and high in moisture and ash, though in some samples the amount of ash is only medium. The heating value of these coals, ranging from 8,568 to 10,359 British thermal units on air-dried samples, and their poor keeping quality indicate that they should be classed as subbituminous coals. The coals bum with a medium-long, orange-colored flame which is smoky under ordinary circumstances. The ash is fine and has a gray color.

The Fort Union coal from the Big Sandy district contains a lower percentage of moisture than those from the other districts, and consequently stocks to better advantage, as it tends to slack more slowly than coal containing high amounts of moisture. The amount of ash varies from medium to high, and the heating value from 10,156 to 10,526 British thermal units on air-dried samples. The coal is therefore subbituminous, but close to the bituminous grade.

The low heating value, the low specific gravity (about 1 .3), the high percentage of volatile matter, and the low percentage of fixed carbon show the coals to be of value for gas-producer purposes and domestic and boiler use.

106 Contributions To Economic Oeolooy, 1908, Pabt H.

Two things are essential to insure the most economical results with fuel of this class when used under boilers. First, as the coal disintegrates rapidly on losing the large percentage of moisture which it contains, it is necessary to use a fine grate similar to the herringbone type in order to minimize the loss of coal passing through the grate bars. Second, a suitably high draft is necessary to insure perfect combustion.

Quantity Of Coal Available.

It has been pointed out in the foregoing pages that the greater part of the field with which this report is concerned is covered by glacial and alluvial deposits and that the complex structure is greatly obscured by this covering. Consequently, at the present time it is difficult to estimate even approximately the total quantity of coal available in the region. Future demands for this grade of fuel may encourage detailed prospecting with the diamond drill, which will give the data necessary for estimating the tonnage of available coal.

Conditions Of Mining And Transportation.

The largest and best-equipped mine in the field is that operated by the Havre Fuel Company, which has installed one of the most modern surface plants in the State. The cars are hauled in the workings of the mine by mules to the foot of the incline, where they are attached to a cable and drawn to the surface by steam power. From this place they are hauled by a 10-ton Baldwin Westinghouse electric locomotive to the tipple, about a mile southeast of the mine. Here they are weighed and automatically dumped, and the coal is loaded into box cars on a spur of the Great Northern Railway which has been built across Milk River from the main line of the railroad at Havre. The only other mine in the field having a steam surface plant is that of the Mackton Coal Company. At this mine the cars are brought to the surface by a steam hoist, dumped into a chute, and conveyed to bins, from which wagons are loaded. Coal from the Staton mine is hauled to Havre partly by wagon and partly by traction engine. A railroad line has been surveyed connecting this property with the main line of the Great Northern Railway at Havre, but as yet no grading has been done. The coal from the other mines in the field is transported by wagon.

The mines in the field employing the largest number of men are those of the Havre Fuel Company, 4 to 30; the Mackton Coal Company, 4 to 16; and the Staton Coal Company, 4 to 10. The other mines and prospects in the area employ from 1 to 3 men each.

The roof and floor in most of the mines and prospects in the field are soft sandstone or carbonaceous shale, making it necessary in

Milk Biveb Coal Field, Montana. 107

most places to leave coal in the roof to keep the entries from caving in. Extensive timbering will be necessary when mining is done on a large scale, and this will add to the cost of producing coal as there is no timber in the field suitable for stuUs, lagging, or props.

Future Development.

As the coal of the Milk River field is high in moisture and slacks rapidly on exposure, it can not be shipped great distances in uncovered cars. The rapid disintegration of the coal when burned, together with its low specific gravity, make it a poor railroad fuel with engine grates of the present pattern and the strong draft of the locomotive, as much of the finely-divided coal would be lost through the grate bars and the stack. Consequently the future development of the area will depend largely on an increase in the population of Milk River valley. If the several large reclamation projects which are proposed in this general region are completed, the population will greatly increase and there will be a greater local demand for the fuel.

A few carload shipments have been made to Seattle and Spokane, Wash., and to Helena, Great Falls, and Conrad, Mont., but the greater part of production, which was 24,847 tons® in 1907, is consumed locally.

o Mineral Resources U. S. for 1907, pt. 2, U. S. Geol. Survey, 1906, p. 50.

Notes On The Coals Of The Custer National

Forest, Montana.

By Carroll H. Wegemann.

Introduction.

General situation. — The Custer National Forest, comprising an area of approximately 950 square miles, lies to the eastward of Tongue River in southeastern Montana, a little north of the Montana- Wyoming line. Its coal field is a part of the broad area of coal-bearing rocks of Eocene age, which extends from North Dakota across Montana far into Wyoming.

In the spring of 1908 it was the writer's privilege to accompany a small party from the Forest Service engaged in the examination of timber in this region. In working from the camps it was impracticable to trace individual coal beds from township to township over the area. Beds were traced in separated localities as time allowed, and for correlation recourse was had to detailed stratigraphic sections. Although data of this nature are sometimes misleading, the information gathered in the four weeks spent on the work was sufficient to warrant the classification of four townships in the northern part of the forest.

Relation to other fields. — The yellow beds of the Fort Union formation are the only rocks exposed within the area. They lie practically flat. To the north thev are continuous with the rocks of the Miles City coal field ;° to the south with the rocks of the Sheridan field of Wyoming.''

Rovtes of travel. — The post-office of Ashland, the home of the forest supervisor, is situated at the junction of Otter Creek with Tongue River and is reached by daily stage from Forsyth, 65 miles away. There is also a main road up Tongue River from Miles City which runs through to Sheridan, Wyo. Stacey post-office, on the northeast border of the forest, is reached by a stage road up Tongue River and Pumpkin Creek from Miles City. There is a good road up Otter Creek, and wagon roads follow most of the larger tributaries of the above-mentioned streams.

Collier, A. J., and Smith, C. D., The Miles City coal field, Montana: Bull. U. S. Ceol. Survey No. 341, 1909, pp. 36-61. b Taff, J. A., The Sheridan coal field, Wyoming: Bull. U. S. Geol. Survey No. 341, 1009, pp. 123-150.

Coals Op Custeb National Forest, Montana. 109

Topography.

The topography may be discussed under three main heads, the lowlands, the badlands, and the uplands. Terraces*occur along Tongue River, but they are of small extent.

The lowlands consist of the present river flood plains. They constitute the lands available for irrigation and are very fertile, alfalfa and oats being the principal crops.

Badlands are not as typically developed in the yellow beds of the Fort Union formation, which show little variation in texture and hardness, as in the alternating hard and soft rocks of the sombercolored beds which underlie them. They are present, however, in this area along certain streams — as, for example. Pumpkin Creek and its tributaries. Here they form a transition zone between the uplands, which are but little affected by erosion, and the river flats, which have been completely leveled. They represent, in fact, the maturely developed topography of the region, sharp ridges and deep canyon-like valleys alternating with one another in such rapid succession that travel across the drainage lines is often difficult.

The uplands rise in abrupt escarpments from the lower levels of the badlands or in places directly from the river flats. Their existence is due to the heavy beds of baked sandstone and shale formed by the burning of the coals of the region. These slags " that cap or rim the uplands effectually retard the down-cutting of the streams which drain them and so protect the uplands from degradation. When the slag cap is once dissected and the soft rocks below are exposed to the conditions of erosion in an arid climate, badlands are formed, provided the main streams have sufficient gradient for rapid cutting and other heavy slag beds do not interrupt the work. Each heavy bed of slag determines an upland area. These may rise one above another in a series of benches to the high divides between the streams. Some of these benches are gently rolling, forming excellent grazing land, and in some places being suitable for farming,'' or the raising of crops without irrigation. Many of the ridges rise 200 to 300 feet above the valley floors. The total thickness of rocks exposed from Tongue River to the crest of the divide is 1,200 feet.

Drainage. — The portion of the forest examined is drained by Tongue River and two of its larger tributaries, Otter and Pumpkin creeks. Tongue River, which follows the western border, rises in the Bighorn Mountains of Wyoming and flows northeastward to join the Yellowstone at Miles City, Mont. The Custer Forest is situated about halfway along its course. Otter Creek rises a little south of the forest and flows northward across it to unite with Tongue River at Ashland. Pumpkin Creek rises on the eastern border of the forest and flows northeastward parallel to Tongue River for a considerable distance; then turning northwesterly it joins the main stream about 12 miles above its mouth.

110 Contbibutions To Economic Geology, 1908, Pabt U.

Stratigraphy. — As has been stated, the only rocks exposed withm the area are the yellow beds of the Fort Union formation, of early Eocene age. In the Miles City district the underlying dark shales of the somber-colored beds are also exposed, and the contact of the two may be traced as one rides up Tongue River. At a point a little below Coleman's ranch, about 10 miles north of Ashland, the sombercolored beds disappear beneath the river. The beds of the Fort Union formation are for the most part white and cream-colored shales and sandstones which present but slight variation in texture and color. At intervals occur thin beds of impure limestone which, being harder than the adjacent rocks, stand out in small ledges. Here and there thin beds of gray shale and of brown carbonaceous shale may be observed, but the beds most easily recognized in the section are the subbituminous coals and the slags formed by their burning. In fact, the coal beds furnish about the only means by which different portions of the section may be recognized.

About 400 feet above the base of the Fort Union formation appears a series of gray sandstones and shales approximately 100 feet in thickness. It contains numerous thin beds of ferruginous limestone which weather brown and red. The resemblance of this part of the Fort Union to the typical somber beds is striking. Whether or not these rocks are constant in character over any considerable area it is impossible to say. Their occurrence is probably of no great importance, simply showing that during the deposition of the Fort Union formation conditions recurred similar to those which prevailed while the somber-colored beds were being deposited.

All these strata are of fresh-water origin. Many of the thin limestone layers contain fossil leaves, and in the dark shales just mentioned there are several thin beds rich in gastropod shells.

Structure. — So far as could be determined the rocks withm the area are horizontal, the dips being too slight to be detected with the instruments employed.

Coal.

General Description.

Coal beds ranging from a few inches to many feet in thickness occur throughout the stratigraphic section in this region. They seem to be fairly constant in thickness and quality over considerable areas, but too much reliance should not be placed on this continuity, for shale seams appear in many places, rendering a coal valueless which at another locality is workable. Coal beds run out into bone or black shale or disappear altogether. On the other hand, if several exposures of good coal are found on the same bed at intervals of a tnile or two, the bed appearing to be fairly constant in thickness and

.COALS OP CUSTEB NATIONAL, FOREST, MONTANA. Ill

quality, it is very probable that the coal is good between the exposures, although it may be completely concealed.

Silicified logs were noted in many of the coal beds. Some of these logs appear as slabs representing but about one-third of the original trunk, the upper side being flat and the lower conforming to the shape of the original log. In some places the logs when partly decayed were undoubtedly crushed and flattened by the load above them, but it is possible that in others as the log lay in the bog the upper portion turned to coal while the lower under different conditions was silicified.

The coal of this field is somewhat darker than the Miles City lignite described by Collier. When first mined it has a brownish cast, but soon blackens on exposure. The grain of the original wood is for the most part well preserved, yet there are seams between the woody layers which have lost all woody structure. In them the coal is black and shiny with conchoidal fracture.

That the coal is subbituminous rather than lignite may be questioned. It lies near the border line between the two. On the whole, it resembles more the subbituminous coals of the Sheridan field than the lignites which occur east of Miles City, being darker than the hitter and containing a greater amount of material in which no woody structure is apparent. The Sheridan coals run as high as 10,000 British thermal units in calorific value; the Miles City lignite runs about 8,200 British thermal units. No samples for analysis were obtained from the Custer Forest, yet an idea of the probable calorific value of the coal may be formed from the values in these

adjoining fields.

Development.

Mining development has made but slight progress in the Custer Forest. Coal is so plentiful that almost every ranch has its own bank, where the coal is obtained by stripping the surface and mining from the open face of the bed. No drift or shaft was seen by the writer, and until a railroad runs up the Tongue River valley the demand for coal must be but local.

Detailed Descriptions.

In the following descriptions the area is taken up by townships, beginning at the northeast comer of the field examined and passing from east to west.

T. 1 S., R. 48 E, — Two beds of good coal with an interval of about 60 feet between them are exposed along a coulee in the southwest comer of this township (PI. VII, No. 1). The lower bed, which is 14 feet in thickness, has been worked to a moderate extent. The upper bed is about 7 feet thick. It has not been prospected at this locality,

112 C0N1Ribx7Ti0Ns To Economic Geology, 1908, Part H.

but about a mile to the southwest it has been mined. Both beds, like most of the coal of this region, have burned widely, forming marked ''slag'* horizons.

North of the Charles Daly ranch in section 18 coal is exposed in a hillside. The bed is at present so obscured by slumping that a measurement could not be obtained. It is stated, however, that this coal is of considerable thickness and was formerly mined. It is by barometer 110 feet below the HTfoot bed in the southwest comer of the township.

The coal outcrops in this township were not mapped. The coal area is probably confined, however, to the southwestern portion, as the beds described have been removed by erosion from the northern part of the township and the presence of lower workable coals is uncertain.

T. 1 S., R, 47 E. — Coal is mined for use at Stacey post-office in section 36 of this township, where about 7 feet of good coal is exposed. The bed probably corresponds to the highest of the three beds in the township to the east (PI. VII, No. IB). No coal outcrops were traced, but it is probable that the greater portion of the township is underlain by workable coal.

T. 1 S.J R. 46 E. — The high' divide between Beaver Creek and Liscom Creek runs across this township from northwest to southeast. Several coal beds are exposed on the higher slopes of this divide, but they underlie comparatively small areas. The important coals for the classification of the township are two in number. North of the Kelsey ranch on Beaver Creek, in sec. 6, T. 1 S., R. 46 E., over 7 feet of coal is exposed in a bank opened by Mr. Kelsey (PI. VII, No. 2A). The coal is of rather inferior quality, containing specks of clay and small particles of pyrite. Its outcrop is indicated on the map. Sixty feet above this coal is a slag which may be traced southeastward up Beaver Creek to an exposure of coal in the NE. sec. 27 (PI. VII, No. 2B). This bed is 11 feet 4 inches in thickness and apparently of good quality. This coal is by barometer 335 feet above Tongue River at the mouth of Beaver Creek. It is probably the same bed as that which is burning about 3 miles north of the Kelsey ranch across the divide, where along a coulee about 20 feet of coal is exposed, but the bed is separated into two benches by 2 feet of brown shale. It is possible that the coal which is here on fire corresponds to one of the two beds which have been described as burning 6 miles northeast of Ashland.

Two other coals occur, one 50, the other 75 feet below the Kelsey bed (PI. VII, No. 2). The lower is 3 feet 4 inches in thickness in the SW. i sec. 7. No lower coal beds of value were observed above the somber-colored beds in passing down Beaver Creek to Tongue River.

Coals Of Custer National Forest, Montana. 113

Liscom Creek within the limits of the township has not cut down to the horizon of the Kelsey coal, so that the whole township, except that portion along Beaver Creek indicated on the map, is probably underlain by workable coal.

T, 2 S., JR. 48 E, — Several coal beds outcrop along the slopes of the divide which occupies the western portion of this township, but the principal coal of the area is the heavy bed indicated on the map. In the NW. sec. 28 this bed outcrops at several points along a coul6e. A pit opened for mining exposes feet of clean coal without reaching the bottom of the bed (PL VII, No. 3A). In the SE. sec. 16 the same coal is exposed, but no other exposures of this bed were found within the township, the outcrop being traced by the heavy slag or clinker formed by the burning of the coal. The valley of Pumpkin Creek may be underlain by the bed of coal outcropping in section 18 of the township to the north. This bed is by barometer about 100 feet below the coal here mapped. There is no assurance of its presence in this township, however.

T. 2 S., i?. 47 £.— The Otter Creek-Pumpkin Creek divide, which reaches an elevation of nearly 4,000 feet above sea level, runs across the southwestern portion of this township. This divide contains several coal beds which are in general burned along the outcrop, but which probably contain much workable coal. Time was not taken to map these upper beds, as it was considered that the classification of the land would depend on the lower beds in the township. Of these there are two outcropping in the valley of Little Pumpkin Creek, in the northeastern portion of the township. A good exposure of the upper bed occurs in the SE. sec. 5. The bed is over 7 feet in thickness and the coal is said to be of excellent quality, burning with but Httle ash (PL VII, No. 4C).

A rather poor exposure of the lower coal occurs in the SW. sec. 35 of the township north of this. About 6 feet of coal were measured here (PI. VII, No. 4B). Across the divide to the northeast coal which is considered to be this same bed has been mined to a small extent in an open bank. Here the coal is 7 feet in thickness. The outcrops of these two beds were "traced in the mapping by means of the slag formed by the burning of the coal along the outcrop.

About 1 mile northeast of the exposure last described a bed 60 feet lower in the section has been worked for local use, and contains 14 feet of good coal. (See T. 1 S., R. 48 E.)

T, 2 8,, R, Jfi E, — This township occupies an area of considerable elevation between Beaver Creek and East Fork. No coal outcrops were traced here, but the whole area is believed to be underlain by workable coals which outcrop at lower levels in adjoining townships.

7963**— Bull. 381—10 8

114 Contbibutions To Economic Geology, 1908, Pabt H.

In the SW. sec. 32 about 7 J feet of good coal is exposed in the bed of a coul and is mined for local use. This coal is by barometer about 400 feet above Ashland.

7*. 2 S., li. Jfi E. — About 6 miles northeast of Ashland, in sec. 7, T. 2 S., K. 45 E., is a considerable area in which two beds of coal are at present on fire. The beds are about 60 feet apart, the lower being 265 feet above Ashland. Neither of these beds is exposed, but to judge by the amount of settling of the surface over the burned area they are of considerable thickness.

jT. S iS., li, Jfi E. — Near the Pete Daly ranch, at the mouth of the East Fork of Otter Creek, 4 miles southeast of Ashland, 38 inches of coal is exposed in the creek bed. The base of the coal is covered. It is probable that this is the same bed as that exposed on Tongue River near Ashland.

T. S 5., /;. U E.—ln sec. 10, T. 3 S., R. 44 E., 1 mile west of Ashland, a coal bed 6 feet 7 inches in thickness outcrops just above the level of Tongue River. The coal is of good quality and has been mined for local use. Six miles down Tongue River from this point, at tlie mouth of Culberts Coulee, a careful examination of the river bluff failed to show any coal over 2 feet in thickness at about this horizon. Whether this bed is thinning toward the north or whether it is simply obscured by the slumping of the soft shales is uncertain.

If the writer's correlations prove to be correct, five workable coal beds occur within the first 400 feet of strata above Ashland. Two higher coals wore measured, one 10 feet in thickness 700 feet above Asliland, the other 11 foot in thickness 650 foot above Ashland. Tlioso are found only on the high divides and extend over comparatively little country. Several heavy slags also were noted, the coals' of which wore not found. No mine openings were found on the two highest hods. This is not because they are inferior in quality to the lower bods, but bocauso, occurring only in the higher hills, they are more dillicult of access.

THE POWDER RIVER COAL FIELD, WYOMING, ADJA- CENT TO THE BURLINGTON RAILROAD.

By R. W. Stone and C. T. Lupton.

Introduction.

The present report is a preliminary statement prepared at the close of the field season, to give advance information concerning the coal resources of a portion of the Powder River coal field, in northeastern Wyoming, adjacent to the Chicago, Burlington and Quincy Railroad.

The Powder River coal field is a small part of a large area of coalbearing rocks, known as the Northern Great Plains Province. Beginning at Casper and Douglas, on North Platte River, in Wyoming, this province extends northward between the Black Hills and Bighorn Mountains, occupies the eastern part of Montana and all the western half of North Dakota, and reaches into Canada. The examination of that part of the province which lies in Wyoming alone is a matter of several years' work. In 1907 a Geological Survey party under J. A. Taff surveyed the Sheridan district, and another under E. W. Shaw examined the south end of the province between Douglas and Casper. In 1908 H. S. Gale surveyed a field in the vicinity of Buffalo and Trabing and the writers examined a block of townships along the Burlington Railroad, adjoining the areas covered by Taff and Gale, and extending to the eastern limit of the coal field.

The area described in this paper lies between Clearmont and Rozet. It has an east-west length of 60 miles and an average width of over 20 miles. It includes practically 1,400 square miles, or 39 townships.

The primary purpose of the investigation was to determine the amount of land underlain by workable coal beds and to locate the eastern limit of the coal field. The writers were assisted by F. D. Morrison and C. M. Holmes, jr., who, in addition to their duties as camp hands, rendered considerable service in making compass traverses, collecting fossils and coal samples, and assisting in the topographic work,

116 Contributions To Economic Geology, 1908, Pabt Ii.

Tlio region under discussion was surveyed by the General Land Offico in 1883, but practically no section comers bearing evidence of having been sot during the original survey could be found. Under those conditions it was useless to follow section lines, and on account of the rough character of the country it was impossible to travel in straight courses and to measure distances by pacing; therefore a 2i-mile base line was measured on the Powder River flat, 6 miles nortli of Arvada, a system of triangulation on prominent buttes was developed, and a topographic map of a part of the area, on a scale of a mile to the inch, was made by the use of 15-inch plane tables and open-sight alidades. A little less than half of the total area, or 600 and 700 square miles, was mapped in this way. The meandering course of Powder River above Arvada was mapped by a foot and compass traverse. The outcrops of the principal coal beds wert> vskotched with the topography. A profile of the Burlington Railroad, Otological Survey bench mai*ks along Clear Creek, and aneroid-barometer readings were used for vertical control.

ANI> COMMERCIAIi RELATION.

The position and outline of the district are shown on the index map (PI. VIII), which also shows its more general geographic nations.

The Rurliiigton Railroad is the only line at present crossing the Powder River coal held in northeastern Wyoming. The construction of a down Powder River to the Yellowstone is feasible, and such a road wouKl make a much larger part of the coal field readUy aoivssible. Thirty-nine townships lying along or close to the railroad, and thenfon mon nadily accessible and open to development whenever H demand arises for this coal, were selcKted for examinmiion bv the writers in 1 WS and constitute the area described in this paper.

Stt tiers an few in this count rv because of the scarcity of water. The principal ivrupation is cattle and sheep raising. Gillette, Arvada, and Cleamiont, the only villages, have a total population of alvnit Gillette is the lanjest, with about 300 people, and Arvada is the smallest, its numbering between 50 and 75, Aside the: villarts on the railroad, settlement is confined to the valloVs of the main stnams. the most desirable land lying along Woman and Clear crooks and Powder River. These stieams are jx-'Tvnnial, bxit all the others in the area aie intermittent, flowing onlv alxMit months in the ve4ir, Alon*: intermittent stieams windmills an iisti commonly for pumping water from deep wells for and domestic use. The Buriinirion Railroad pumps water deep wells at Felix and Gillette to supply its locomotives and section men. It is a common pmctice among the ranchers to store

Powder River Coal Field, Wyoming. 117

ice for drinking water during the summer as the ice water contains much less alkali and sediment than the normal stream flow.

Timber is scarce in this area, being limited almost entirely to Cottonwood along the main stream courses and to scattering pine and cedar in the hills.

Topography.

The Powder River coal field lies in the Great Plains province, between the Bighorn Mountains and the Black Hills. Much of it is 80 deeply dissected that the original plains character is suggested and represented now only by the crests of the main ridges, which are all at about the same elevation. The topography of the region between Clearmont and Oriva is mainly of the badland type, especially close to the main streams, but there are small areas of more gentle relief in Tps. 54 and 55 N., R. 76 W. Vegetation is scanty and when rain falls numerous rivulets form, each carving a channel in the soft clay or sand. The result is an intricately dissected and irregular surface over which it is difficult to travel. East of Oriva the topography is in large part of moderate relief, although there are some areas of extreme dissection.

In the badland areas bare slopes are everywhere conspicuous. From elevated points in these areas one sees innumerable steep-sided ridges, buttes, domes, precipitous bluffs, and, in places of recent sharp dissection, pinnacles capping the ridges and old valley bottoms dissected by vertical-walled coul6es.

In some parts of the area the coal beds are burned along the outcrop, the overlying clay being baked to a resistant mass that forms ledges in the steep sides and caps small mesas and numerous detached buttes.

The areas of more gentle topography are grass-covered and prairielike and exposures of bed rock are much less common in them than in the badland areas.

The altitude of the region ranges from about 3,600 feet above sea level on Powder River at the mouth of Clear Creek to about 4,900 feet on the hilltops in the divide near Sparta, west of Gillette.

Geology.

The rocks of this area consist of a series of clay, shale, sandstone, and coal beds, alternately stratified, apparently conformable throughout, and belonging to the Fort Union formation. In the Sheridan field the formation was divided Taff on lithologic grounds into a lower member, consisting of 2,500 to 2,800 feet of dull-drab, bluish, and brown shale, and an upper member, consisting of 2,200 feet of bluish and brownish shales and sandstones intei-stratified with many coal beds. He also subdivided the upper member into the Tongue

118 cosruiiiirnotH to kconomic geology, 1908, part n.

Ki vir, ami Ulm rml groujis, and this grouping will be foll()Wi*(l in th ]}rvHimi papr for convenience of description.

TIh? \imcr is exposed in this area only east of the line of biutud rock extending north and south through Mintum and marking eastern limit of the coal field. These beds are essentially all <'Jiiy or shiih and an ])revailingly light colored. They contain bands of (ltd! nnl and brown beds which, where weathered and washed down, may nuiNk the lighter beds and give a dull color to the whole. These IhmIn uIho contain numerous nodular concretions ranging up to several feet in length, which, because of their iron content, on weathering beyellow or rusty to dark brown. In clean-washed slopes these nodides nuke ctmspicuous dark spots in the light-colored clay; on dee])ly weathered slopes where the nodules are abundant and disintegra((d to fragments they give a dark tone to the surface.

Th( thickneNN of the lower member in this area is not readily measurable, but nuiy approximate 1,000 feet. The member contains two tlu'ee coal beds less than a foot thick.

Above t luse beds is a series of clay, sandstone, and coal beds called by TaiV the Tongue River coal group, from their occurrence on that Htivam. At the type locality the group is about 800 feet thick and etuituins seven workable coal beds. In the Powder River field the outciH>]is between Minturn and Gillette in a north-south belt, but it is so tiltetl and burnett that its thickness can not be measured. A portion of the coal is exposed also on Powder River, 6 to 10 miles below ,Vrvudn Between the lowest rocks on Powder River at the state the highest IhhIs of the group is an interval of 575 feet containing at least tive coal IhhIs. As the boise of the group is \mder cover at the state line the total thickness was not determined.

(>n Kiver the sequence of coal IhhIs is as follows:

luvoniil , 210

luisNo Mnxi S

Powder River Coal Field, Wyoming. 119

shale on the other. The sand is m general only slightly consolidated and for the most part is light colored, white or slightly iron stained, givmg to the coal group the name ''yellow beds/' In places the sand is cemented by iron or lime and forms ledges. The beds of sand vary in thickness from mere streaks to great masses measuring from 40 to 100 feet. Cross-bedding is common, but grits are rarely found. Owing to the horizontal position of the beds and the numerous large bare exposures in the badlands along the river, the thick beds of white sand can be traced with the eye for miles.

The Intermediate coal group, which is described by Taff as having a thickness of 1,150 feet in the Sheridan district and extending from the Roland coal bed up to the Lower Ulm coal bed, in this district seems to be about 900 feet thick. Sand and clay, with less abundant beds of shale, compose the group. It is more sandy in the lower than in the upper half. Bands of brown carbonaceous shale are scattered throughout, being the more numerous perhaps in the upper part. A conspicuous feature of the lower part of the group is a fossil shell bed which occurs about 175 feet above the Roland coal bed and which is so continuous and so readily seen as to make an excellent horizon marker. Above this shell bed, in places resting on it and elsewhere separated from it by 30 to 40 feet of sand, is a workable bed of coal. This is the lower coal of the two workable beds found in the group in this area. It is called the Arvada coal bed, from its occurrence at that place. The other is the Felix coal bed, which occurs about 350 feet higher in the section and has been mined at Felix, Echeta, and Croton, on Wildhorse Creek.

The Ulm coal group comprises the highest beds in the Powder River field. Its base is marked by a bed of coal which is widely distributed and which is found about 350 feet above the Felix coal bed. In the Sheridan district erosion has largely removed this bed and in the Powder River field it is found only in the highest hills, where it has been extensively burned along its outcrop. That part of the group which has not been eroded is nearly all white sand and is about 150 feet thick. Bands of carbonaceous shale, which may represent the horizon of the Upper Ulm coal bed, cap the geologic section in this district.

Baked shale and clay, made bright red by the burning of an underlying coal bed, occur at the various coal horizons in nearly all parts of the field.

Collections of fossil plants and shells made in this and adjoining districts have been examined by F. H. Kjiowlton and T. W. Stanton, who agree that the beds from which the fossils were obtained are of Fort Union age. This determination makes the age of the coalbearing rocks basal Tertiary, or, more definitely, lower Eocene.

120 Contributions To Economic Geology, 1908, Pakt Ii.

The geologic structure of the region is extremely simple. As has been described and figured by Darton," the country between the Bighorn Mountains and the Black Hills is a shallow structural trough having a steep western rim. In this rim the rocks dip sharply away from the Bighorn Mountains, but in the vicinity of Clearmont they are practically horizontal. The beds lie flat through the Powder River and Wildhorse Creek country, but begin to dip slightly to the west near Oriva. Frorn this point eastward to Mintum the dip increases to a maximum of about and flattens again near Rozet. The westward dip near Gillette is sufficient to bring the Tongue River coal group to the surface within a short distance. This slight monocline, near Gillette, strikes nearly north and south and determines the eastern limit of the coal field. Besides the main structural features there are minor warpings of the strata, but the vertical control of the map work was not of sufficient accuracy nor the plan of the work detailed enough to determine the amount or extent of the irregularities. One of the most conspicuous of the minor features is a low wave in the structure at the mouth of Twentymile Creek, just

east of Echeta.

The Coal.

Description Of Coal Beds.

General Outline.

In a brief preliminary report it is not possible to offer all the details of the geologic section or to give a large number of close measurements of coal beds. Neither is it possible to state with definiteness the correlation of certain features throughout the area described or their relation to adjoining areas. For this reason the statements which follow are in part somewhat generalized. They are intended to give the conclusions concerning the area and a fair amount of the data on which the conclusions are based. The accompanying map (PI. VIII) showing the distribution of the coal beds was reduced from the original map, contour lines being omitted. In a subsequent report, prepared after the material in hand has been more thoroughly studied, it will be possible to give more details of the numerous coal beds and to discuss scientific questions.

The principal coal beds in this area are five or more in number. They are generally free from partings of clay or shale and are of considerable known extent. The field work of 1908 was done under the coal-land classification schedule, which considered subbituminous coal less than 4 feet thick as nonworkable. Although it is possible that beds of coal less than 4 feet thick may be mined in this field in the distant future, the distribution of beds of much greater thickness is so widespread that those less than 4 feet thick were not mapped.

a Prof. Paper U. S. Geol. Survey No. 32, 1905.

Powder River Coal Field, Wyoming. 121

The beds of coal which will be described are as follows :

Principal coal beds in Powder River field.

Feet.

Lower Ulm or Healy coal bed 10- 15

Interval 300

Felix coal bed 6-30

Interval 375-400

Arvada coal bed 5- 10

Interval 125-225

Roland coal bed 3- 7

Interval 80

Smith coal bed 4-10

Besides the coal beds named above, there are numerous other beds of coal distributed throughout the geologic section above described. They range from a few inches to several feet in thickness, but the thicker beds are of small geographic extent.

The description of the coal beds will begin with the lowest in the geologic column exposed in this area and give briefly the character of the bed, its extent, and the points where it is well exposed.

Smith Coal Bed.

A coal bed which outcrops at or just above water level along the lower course of Clear Creek is believed to be the same as the Smith coal bed of the Sheridan field, described by Taff as occurring about 560 feet above the well-known Monarch coal bed. The best exposures of this bed are in the cut banks of Clear Cfeek in the northern part of T. 55 N., R. 78 W., where it has an almost constant thickness of 10 feet of clean coal. An analysis of a sample (No. 6460) cut from a fresh face in the creek bank (No.2) in the NW. NW. sec. 12, T. 55 N., R. 78 W., is given in the table on page 133. A coal bed at about the same horizon occurring about 75 feet above Powder River at the northwest comer of sec. 2, T. 55 N., R. 77 W., near the Lynn ranch has a thickness of 4 feet 3 inches. The outcrop of this bed along Powder River is not shown on the map.

Because of the practically horizontal position of the rocks and the fact that this coal is near water level in the lowest part of the district, it is readily seen that if this bed is continuous it must underlie the entire coal areaof this field.

Roland Coal Bed.

A coal bed at the top of the Tongue River coal group, described by TaflF as having a thicknet of 13 feet in the Sheridan district but diminishing to 2 feet toward the south, was called by him the Roland coal. A coal bed in the Powder River field having about the same geologic position, 150 feet below a conspicuous bed of fossil shells,

a Numbers in parentheses refer to locations on the map (PI. VIII).

ta ropyctpfrfiojift lo 9%y: ovAijer* ttK. pakt n.

IQM'/f ir tA/ifc //f yfWfU Hir0fr ml wMUrr fcrel by the mU uotiU Arvft/I*. Ifrm it has a thickneas of 7 feet, whidi it tuMUiMtvi fm ({hinnce, aa it is 7 feet thick near the \jyuu fMts'h $fu Mint at the north edge of the same township. ifu tUm C.ffk \itni mmih f4 the towmhip line (So. 7) in T. 55 X., R. 70 W/ Mi Wfihwi iUfn\ lyin beneath 20 to 30 feet of massive buff nnwinUfUtf in in two b#;nr;h#m, the upper one 7 feet 8 inches thick nwl Mmi Utwttr ntu 2 Uuti 3 inches thick separated by 3 feet of gray

On (ImU in m*v. 31, T. M N., R. 77 W., in the hills north of tliM ('UhfiMi f', what in to be the same bed has a thickness of ttHii H Uu'him, Uu'Uulinr a O-inch parting of brown shale. The of (JiIn on (*li*ar Orock in not shown on the map. As this i'mmI ImmI thn rivor at (campbell's, the outcrop in the Mi'MM hiM'M ilnwcrilMMl iii of Niniill extent. TIio bed certainly is worthy iif Monin rofiwiilnnil ion on Powdor River, but whether it is of workable lhli*hnnM for nny Hintiuico wliere deeply buried is a question wlilrli no( hr iinNwrrrd initil tlio area has been prospected by Iho drill.

Akvada Iiki).

Tlio mnno Arvmlu is to a oonl hod in the lower part of the Ai N nda, on KivtM\ About 1 nulo above Arvada this coal is at lovol, and Wildlunso CixMk it disappoai at the junction of tho and south forks. Ii outri\>ps for a of miles on i'loar i'lvok* bolow watiM lovol at the railnad bridge west of U ol a ImsI of >;raN vandsiono larrvini: an abundance of laige and w vx than ihc twk aK c and Ivlow thai it a kstviv xN\ op a tahi of solid . I'sually the sheUs MMUC plaxCv tV,c V\\ax5a coa! viirvily on the fiX55?il bed,

Powder Riveb Coal Field, Wyoming. 123

west side of Clear Creek (No. 1), in sec. 3, T. 55 N., R. 78 W., the Arvada coal bed has been dug by ranchers from the outcrop in the bank of a small tributary. The section of the coal bed at this point is as follows:

Section of Arvada coal bed near Davis ford (No. 1), sec. 5, T. 55 JV., R. 78 W.

Ft. in.

Coal 9

Shale brown carbonaceous 2

Coal 2 6

The coal here is separated from the fossiliferous sandstone below by 3 feet of brown shale.

J. N. Sweat has opened a mine on this coal bed in a ravine IJ miles north of Kendrick (No. 3), in the NE. i sec. 13, T. 55 N., R. 78 W. Here the bed averages 9 feet in thickness and is free from partings other than a half-inch streak of mineral charcoal.

The record of a well drilled at Gillette by the Burlington Railroad shows at a depth of 350 feet a coal bed reported to be 55 feet thick. The writers believe that this bed is at about the same geologic position as the Arvada coal, but question whether its thickness is so great as stated. It is likely that there is coal of considerable thickness, but it is probable that a part of the bed is brown shale; at least the evidence afforded by sand pumpings from a chum drill is not wholly conclusive.

From the character of the Arvada coal bed on Clear Creek, Powder River, and Wildhorse Creek, it may be concluded with some certainty that this bed underlies a considerable part of the area mapped and that it is of workable thickness.

Samples of the Arvada coal were taken at the Sweat mine (No. 6798) near Kendrick (No. 3), and at the Arvada mine (No. 9). At the latter point two samples were taken, one (No. 6459) representing the whole bed, and the other (No. 6461) representing the lower half or blocky part of the bed. Analyses are given on page 133.

Felix Coal Bed.

At elix, a station on the Burlington Railroad near the head of Wildhorse Creek, a thick bed of coal is conspicuously exposed both on the main stream and in a draw on the north. Being close to the railroad it attracted attention and a mine was opened here a dozen or more years ago. It will be called in this report the Felix coal bed, as this is probably the first place in the region where the bed was worked.

The position of the Felix coal bed is about 375 to 400 feet above the Arvada coal bed, or near the middle of the Intermediate coal group. East of Powder River it is for the most part 10 feet or more thick, is

124 Contributions To Economic Geology, 1908, Part U.

readily found in natural exposures in many coul6es, and where biimed is traced without difficulty by the red baked clay. Like the other beds of workable thickness in this area it consists of solid coal practically free from partings.

An exposure of tliis coal bed in the bank of Wildhorse Creek, onetliird mile below Felix (No. 20) has an apparent thickness of 40 to 50 feet. That this is the result of a slip was proved by a drift at the base running through the coal into clay. The bed at this point is actually about 16 feet thick. A small mine was opened here and operated for a sliort tune. On the first tributary of Wildhorse Creek entering from the north below Felix this bed is exposed at two or three points and is between 20 and 25 feet thick. The outcrop is maintained at water level for some distance by a slight westerly dip of the rocks.

The easternmost occurrence of the Felix coal bed in this area is at Gillotto. Here tlie rise of the rocks brings the bed to the surface and carries it above the plains to the east. The coal is mined 1 mile west of town bv W. F. Vines. The section at his mine is as follows:

Section of Felix coal bed at the Vities mine Gillette.

Ft. in.

Coal, with clay bands to 1 foot thick 9 10

Shalo and clay 1 6

Coal 1

CI ay , d ral> 5

8halo, bituminons 8

Coal, cloan and wlid 7 6

25 6

Steven miles duo south of GiHotte on the west side of tJie road (No, 27) in sec. 34, T. 49 N., K. 72 W., the FoUx coal bed, exposed in natural and alsi> partly excavated, has a thickness of 22 fivt, the 7 tliin bands of shale. Where this Caballo Ciwk, 7 miles farther south (Xo, 28>, a thickness of 0 fott S inches of is oxposotl in the creek bank. The bottom of the Kvl is not visible.

IV H. Uarker mines the Felix in a ravine about miles of Gillotto vXo. whon it lias tho foilowinir section:

CvxaI n

iX-ijU

iKr stirftv is pvon iXtv tvV42 in tho lahlo on pijo ci the lV*rkor tho iiodid <rf Riwhido Civk, tho boJ is si.>!mewitiit

Powdeb River Coal. Field, Wyoming. 125

thicker. An exposure ia the draw 2 to 3 miles north of Sparta is as follows (No. 24) :

Section of Felix coal bed near Sparta (No. 24).

Ft. In.

Coal 14

Clay, carbonaceous 3

Coal, woody structure, poor 2

Shale and clay, carbonaceous 5 6

Coal 9

On a branch of Rawhide Creek 3 miles northeast of Oriva (No. 23) the Felix coal bed is in two benches, but shows some variations from the section last given.

Section of Felix coal bed northeast of Oriva (No, iS).

Ft. in.

Coal 13

Shale and clay, carbonaceous 4 3

Coal, woody structure, poor 2

Shale and clay, carbonaceous 4

Coal 8

In the vicinity of Echeta the thick Felix coal bed is contained in massive white sandstone. Talus from the sandstone above, which is readily traced for miles, commonly conceals the coal. Grood exposures at wide intervals show that the coal bed maintains a considerable thickness over a large area in this part of the district. On Twentymile Creek, near the E. W. Haines ranch (No. 17), in sec. 18, T. 52 N., R. 74 W., the bed is well exposed and shows a clean face of 19 feet of coal with only three partings of clay, each less than 1 inch thick.

At Echeta the Felix coal bed has the greatest thickness seen in the district. In a ravine one-fourth mile west of the railroad station (No. 18) the bed is well exposed, one of the side gulches being wholly in the coal. Here the total thickness of the bed, which is free from partings, is fully 30 feet. An entry has been driven 60 feet on the coal. A sample taken at the face of the entry, including about 8 feet of the middle of the bed, gave the results (No. 6448) shown in the table of analyses, page 133.

The Martin mine was opened on the Felix coal bed at Ooton (No. 16) in 1902. Its development, however, never extended beyond a single drift without rooms. The bed at this point is 11 feet thick and the quality of coal is shown in analysis No. 6432 on page 133. In the hills north of Croton, reached by a rough road from Whittenmeyer's ranch, this coal bed is exposed in a number of coulees (No. 15) and ranges in thickness from 12 to 14 feet. It is overlain by about 50 feet of white sandstone and underlain by 20 feet of similar mate-

126 Contributions To Economic Geology, 1908, Pakt Ii.

rial. On the north side of the ridge between the south and middle forks of Wildhorse Creek (No. 14), in sec. 36, T. 54 N., R. 76 W., this hod has a tliickness of over 16 feet, but in the hills between the middle and north forks and in T. 55 N., R. 76 W., it is commonly from 4 to 6 feet thick. It is exposed at the road gaps in sees. 22 and 2S (No. 8), T. 55 N., R. 76 W., in the midst of a considerable thickness of brown shale, and in each place is 6 feet thick.

About 4 miles southeast of Arvada, in the hills behind Tinkham Butte (No. 10), the Felix coal bed is 10 feet thick without partings, and farther south, in the hills west of Lorah's ranch, 1 mile below the mouth of Crazy Woman Creek (No. 12), it measures 9 feet 6 inches. Here the massive yellowish-white sandstone commonly occurring above the coal is separated from it by 23 feet of drab clay. Near Pendorgraft's ranch, on the west bank of Powder River 2 miles above t he mouth of Oazy Woman Crock, the bed is much thinner.

Section of Felix coal bed near PendergrafVs ranch.

Shale, oarboimceous.

Ft.

in.

On tho east side of Powder River, however, about 1 mile above the mouth of Fortification Creek, the following section was measured:

ytctinn of'civil bed above Fortification Creek.

Ft. In.

rhu . drub 4

Shalo. 1

vMay. vlr.ib

o

A little farther south, alxut one-fourth mile east of the river, on the east side of sv, -V\ T. oJ N.. K. 77 W.. the same bed shows fivt inches of clean coal; and still father south, on the east bank of the river in sv. oJ, the seinion is as follows:

il"

n.

a 5

Powder Riveb Coal. Field, Wyoming. 127

These sections show that the Felix coal bed near the Pendergraft ranch varies considerably in thickness. East of the mouth of Crazy Woman Creek the bed shows 9 feet of coal in clean exposure in the coulees a mile or more back from the river.

West of Powder River, in the valley of Crazy Woman Creek, the Felix coal bed is thinner, and where it passes below water level 5 miles above the mouth of the creek it measures 5 feet.

Lower Ulm Coal Bed.

The Lower Ulm coal bed is about 400 feet above the Felix coal and is considered by Taff as the basal member of the subdivision which he calls the Ulm coal group. This coal in the Buffalo district is described by Gale as the Healy coal bed. ,

High in the hills over the greater portion of the area under discussion there is commonly a band of red baked clay which probably indicates the position of the burned outcrop of the Lower Ulm coal bed. In some portions of the area the abundance of baked rock suggests that practically the entire bed has been consumed, but in other portions the burning is limited to the spurs and unbumed coal is foimd at the heads of the draws. The amount of burned material and outcrops of unbumed coal indicate that the bed is of considerable thickness and therefore of some value.

This coal bed is not known to occur north of the railroad on the west side of Powder River, but between the railroad and Crazy Woman Creek its position is readily traced by the baked clay. Outcrops of the unbumed coal in this locality are few. The best exposure known to the writers is about 8 miles south of Arvada and 3 miles northwest of the schoolhouse near Stott's ranch on Powder River (No. 11). At this point the section of the coal bed is as follows :

Section of Lower Ulm coal bed in sec. 29, T. 53 N., R. 77 W. (No. 11).

Ft In.

Coal 2 6

Shale, carbonaceous 2

Coal 11

Shale, carbonaceous 1

Coal 1 6

The coal in the upper and lower benches of this section is somewhat dirty and therefore of little value, but that of the 11-foot bench is hard and clean. An analysis of it (No. 6444, p. 134) shows only 3 per cent of ash and less than 7 per cent of moisture when air dried.

In the hills on the west side of T. 52 N., R. 78 W., there is a coal a little over 5 feet thick. This probably corresponds with what is known as the Healy coal in the townships farther west. In the high

128 Contbibutions To Economic Geology, 1908, Part H.

butte 4 miles southwest of tiie mouth of Crazy Woman Creek, about 400 feet above the Felix coal, there are two beds of coal separated by 10 feet of clay. The upper bed is 2 feet and the lower one 4 feet thick. Whether these are at the horizon of the Lower Ulm coal bed is a question. It is possible that a thick bed of brown carbonaceous shale occurring about 75 feet below is at the proper horizon for the coal bed under discussion.

East of Powder River the extent and thickness of the Lower Ulm coal bed are well determined by good exposures. Northwest of Croton, in the top of the ridge between Wildhorse and Deer creeks, this coal bed has a thickness of 12 feet 6 inches, and at the head of Deer Creek (No. 13) it was found at one point 10 feet thick and at another 11 feet 3 inches. West of Felix, in the SE. i sec. 16, T. 51 N., R. 75 W., in the head of the coulfie which drains to the east (No. 19) the Lower Ulm coal bed measures 11 feet 10 inches without partings. South of the last-mentioned locality, probably in sec. 32, T. 51 N., R. 75 W., there are good exposures which show at least 10 feet of coal, and on Caballo Creek east of the 4 J ranch, in the southern part of T. 48 N., R. 74 W., it is at least 8 feet thick.

On the heads of Wildhorse and Rawhide creeks, north of Oriva, the Lower Ulm coal bed is burned extensively and probably only a little of it remains. The baked clay that marks the horizon is so resistant that it forms small mesas and round buttes, which give to the topography of this area an appearance somewhat different from that observed elsewhere in the field. Instead of the badlands which abound along Powder River, the surface here is that of a prairie thickly set with small round buttes, each with a capping of red baked clay. The amount of burning suggests that the coal bed in this locality was thick. Evidence on this point is shown at an outcrop on the east face of the hill 1 mile northeast of Sparta (No. 25):

Section of Lower Ulm coal bed near Sparta (No. 25).

Ft. In.

Coal 9

Shale, brown, woody 2

Coal 10 3

Shale, carbonaceous 5

Coal 6 3

Shale, brown, woody 4

Coal 6

26 11

This outcrop marks practically the oastorn limit of the Lower Ulm coal bed, for the monocline extending north and south brings lower rocks to the surface within a short distance. There are a few outliers farther east, but it is that in most of these the coal is burned. Antelope Butte, 8 miles south of Gillette, is capped by baked clay marking the horizon of this coal.

Powder River Coal Field, Wyoming. 129

Other Coal Beds.

The eastern limit of the Powder River coal field is determined by a broad irregular belt of baked clay and slag which extends north and south from the railroad in Rs. 71 and 72. The coal beds that have been the source of this burning are exposed at only a few places. Near Mintum a coal bed which has been prospected by Andrew Ditto in the NE. J sec. 2, T. 49 N., R. 71 W., measures as follows:

Section of coal bed and associated rocks near Mintum.

Ft. In.

Clay, pandy 15

Shale, brown, woody, with coal streaks 3

Clay, drab 4

Clay, sandy, yellow 3

Shale, brown, woody, thin roal streaks. .' 19

Coal 2 6

Shale, brown, woody 1 10

Coal 10

Clay, brown and black 1

Coal, base of bed not reached 8-f

Total coal 11 4-f

It is reported that a prospect sunk 18 feet on this lower bench failed to reach the bottom of the coal.

Nine miles north of Gillette, in the NE. i sec. 10, T. 51 N., R. 72 W., at what is known as the Hulbert mine (No. 22), there is a coal bed similar to the one at Mintum.

Section of coal bed at Ilulbert mine {No. iiJ).

Feet.

Sandstone, yellowish gray, with lenses of clay, brown 20

Coal and brown shale 6

Coal, good, bottom not reached 22 -f

Neighboring ranchers obtain fuel here and some has been hauled by wagon to Gillette. An analysis (No. 6602) of a sample taken at this mine is given in the table on page 134.

The following section (No. 21) was measured about 7 miles farther north, at the western edge of the burned area in the NE. J sec. 3, T. 52 N., R. 72 W. It represents the coal bed 2 miles north of John Grant's ranch.

Section of coal bed in sec. S, T. 52 N., R. 12 W. {No. 21).

Feet.

Sand and sandstone 10d=

Clay, drab lodb

Coal and brown shale 4

Coal, good, black 16

Coal, fair, brownish 5

Clay, yellow 1

Clay, drab 6

Total coal 25

7f3"— Hull. ;W1— 10 J)

130 Contributions To Economic Geology, 1908, Pakt Ii.

This bed is well exposed in a bluff, and Mr. Grant obtains coal here by prying it from the outcrop with a crowbar.

The three outcrops described above are at the western limit of the slag-covered area. In view of this fact and the similarity of the sections, it seems possible that these are all sections of the same coal bed, but they could not be correlated owing to the lack of expoeuree.

The Chicago, Burlington and Quincy Railroad Company sunk a chum-drill hole to a depth of 865 feet at Gillette in 1897 to procure a supply of water. In 1906 a second hole, within a few feet of the first, was drilled to a depth of 1,560 feet. Generalized sections of these wells as reported are given below :

Sections of water wells at Gillette.

No. 1. Xo. 2.

Feet. V9tL

Sandstone and shale 345 Soil, shale, and sandj'tone :. 335

Coal 55 Shale, dark, with coal streak.* 65

Shale, white, black, and blue 85 Clay, shale, and sandstone 90

Coal 35 *Coal 22

Shale and sandstone 345 Shale, sandstone, and limestone. . . 1, 048

865 i.seo

In the first well, at 345 feet below the surface, 55 feet of coal is recorded; in the second well, at the same depth, 65 feet of dark shale with coal streaks is reported. As the wells are only a few feet apart, and such an abrupt change in character in so short a distance is not common, this carbonaceous member is probably the same in both wells. Pumpings were not kept, however, and there is no way of telling whether it is actually a very thick bod of solid coal or a series of alternating beds of dark shale and coal. In both wells, at about 490 feet below the surface, or 85 to 90 feet below the upper coal, there is a second coal bed of considerable thickness. It is recorded in one as 35 feet and in the other as 22 thick. The first well was sunk 345 feet and the second well 1,048 feet below the lower coal without finding another coal bed. It seems probable that these two thick coal beds, 90 feet apart, the upper one at a depth of 340 feet below the surface, at Gillette, are tlie ones that outcrop at Minturn, 6 miles to the east, and have the source of the burning over the broad, irregular belt mentioned above. At least they belong in the Tongue KivcM* coal group.

Besides the coal beds already described there are a number of others, {)robably of local extent only, which are in places of workable thickness. In the vicinity of Px'heta tliere is a 5-foot coal bed about

ft

150 feet above the Felix coal bed and overlain hv white sandstone. What may the same bed is present east of Tinkham Butte, also underlying a white sandstone but much thicker and with a number of partings, in reality a mass of drab chiy and brown, woody shale, containing beds of coal varying in thickness up to 2 feet 6

Mgton

Powder River Coal Field, Wyoming. 131

inches. Still higher in the section, possibly 50 feet below the Lower Ulm coal, there is a bed exposed at the head of Deer Creek, which has the following section:

Section of coal bed at head of Deer Creek.

Ft. In.

Coal and lo.v'A v/(xk1 2

Clay, gray 3 4

Clay, drab I 8

Coal 3

Shale, brown, woody 2

Clay, drab 4

Coal 1

Considering the number and extent of the coal beds, averaging over 10 feet in thickness, already described, it seems unnecessary to give further details of the lesser beds.

Location of mines, prospects, and outcrops in the Powder River coal Md, Wyoming,

adjacent to the Chicago, Burlington and Quincy Railroad.

No. on ri. Ixxratlon. Page.

1 Near Davis ford, sec. 3, T. 65 N., R. 7cl W 123

2 i Bank of Clear Creek, sec. 12, T. 65 N., R. 78 W 121

3 i 14 miles north of Kcndrick, sec. 13, T. 65 N., R. W 123

4 Near Lynn's ranch, sec. 3. T. 65 N., R. 77 W 122

6 CampMl's ranch, sec. 22. T. 65 N., R. 77 W I 122

6 I Near Camplieli's ranch, sec. 27, T. 65 N., R. 77 W i 122

7 ' Joe Creek, sec. 6, T. 65 N.. R. 76 W ' 122

8 ' 7 miles northeast of sec. 2<, T. 66 N., R. 7ii W ! 126

9 Near.Vrvada. sec. 21. T. 64 N.. R. 77 W 122

10 ' 4 miles southeast of 31, T. 54 N., K. 76 W 126

11 I 4 miles northwest of Stott's ranch, sec. 2J, T. 63 N.. R. 77 127

12 ' Lorah's ranch, sec. 9, T. 62 N.. R. 77 W 126

13 , Head of Deer Creek, sec. 14, T. 62 N., R. 75 W

6 miles north of Croton, sec. 36, T. 64 N., R. 7 i

4 miles north of Croton , sec. 14. T. 63 N., R. 70 W

Croton. .vc. 2. T. 62 N. R. 76 W

Haim's ranch, sec. 18, T. 52 N., R. 74 W

Echeta, sec. 2S, T. 52 N., R. 75 W

3 mUe s west of Felix, sec. 16. T. 61 N., R. 76 W

fVllx ' sec. 13. T. 61 N., R. 75 W

2 miles north of Grant's ranch, sec. 3. T. 62 N., R. 72 \v'

HuUiert mine. 9 miles north of Gillette, sec. 10, T. 51 N., R. 72

3 miles northeast of Oriva. 34. T. 61 N.. R. 73

3 miles north of Sparta, sec. 2. T. 50 N., R. 73 W

12K

la's

26 . 1 mile northeast of Sparta, sec. 13. T. 50 N.. R. 73 W 128

26 I Barker mme. west of Gil'etle. sec. 18. T. 60 N.. R. ',2 124

27 ! 7 miles south of Gillette, stv. 34. T. 49 N., R. 72 W ' 124

28 ' Caballo Cn'ck, sec. 36, T. 48 N., R. 72 W 1-.4

Character Of The Coal.

Physical Properties.

All the coal in this district is subbituminous, of the variety commonly called black lignite, and varies but little in the diflferent beds and in diflferent parts of the area. The fresh coal is shiny black and the weathered coal is dull black. It reduces to a black but the streak made on unglazed porcelain is dark brown. The fresh coal is tough and emits a dull sound when struck sharply with a hammer. In texture it is either dense* or woody. In some of the coal having woody texture the grain of the wood from wliich it

132 Contributions To Economic Geology, 1908, Part Ii.

originated is perfectly preserved. This feature of the coal is most common in the eastern part of the field; it occurs at the Arvada mine and at other points as far west as Powder River, but is said to be rare in the coals mined in the vicinity of Sheridan. The specific gravity is about 1.3.

Close examination of the apparently dense and homogeneous coal shows that it is minutely banded. The predominating dull black is brightened by paper-thin discontinuous bands of jet-black coal.

When exposed to a dry atmosphere, subbituminous coal begins to check at once. The checking may be along the bedding and at right angles to it, or in irregularly disposed, hackley lines, resulting in chips very irregular in shape bounded by conchoidal faces. The checking is due to the evaporation of the moisture contained in the coal and is accompanied by a snapping sound. A lump of tliis coal freshly mined and exposed to the hot sun will be deeply checked in a few hours and will readily fall to pieces.

Subbituminous coal is distinguished from lignite by its color, the former being black and the latter brown, and from bituminous coal by the manner in which it weathers. Bituminous coal breaks along straight cleavage plains into prisms and disintegrates very slowly on exposure to the weather.

Subbituminous coal bums with a short yellowish-red flame and for a short time after ignition emits a white smoke that has a bituminous odor. After the early combustion of tlie volatile matter the coal continues to burn with scarcely perceptible smoke. It leaves a fine white ash.

Small globules of resin are found in some of the coal and commonly there is less than 2 per cent of sul[)hur. Thin bands of mineral charcoal are also present.

Chemical Properties.

Nine samples of coal were collected in this district for chemical analysis. They were taken from freshly exposed faces of the beds in prospects and small mines in different parts of the field and should fairly represent the quality of tlie coal, so far as it may be represented by samples from a field where absolutely unweathered coal is unobtainable for lack of deep mines. In collecting]: these samples the surface of the coal bed was cleaned to get rid of any dirt, and all weathered or checked coal was careful! v removed, so that tlie analvsis might represent as nearly fresh coal as possible. A groove was then cut in this clean surface from the top to tlie bottom of the bed. The coal thus obtained was caught on a rubber blanket or piece of canvas to keep out dirt and moisture from the floor, was crushed to i-inch size, thoroughly mixed, and quartered, the (quarters discarded, and the remainder remixed. This jirocoss was continued until the sample was reduced to 1 quart, which was carefully sealed in a galvanized-iron can and sent to the chemical laboratory.

, Field, Wyoming.

ha

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134 Contributions To Economic Geology, 1908, Part Ii.

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Powder River Coal Field, Wyoming. 135

The air-dried samples show an average of 8.05 per cent moisture, 7.22 per cent ash, and 1.60 per cent sulphur. The heating value of these coals is shown by the calorific determinations to be practically the same as that of the coals in the Sheridan field.

Utilization.

The coal resources of this field are practically undeveloped. Scanty population in the area and the production of coal on a large scale in the Sheridan field have retarded development here. There are several openings and prospects from which ranchers and others obtain coal for winter use, but no active mining is carried on. The more important of these openings are described below.

A small mine was opened at Kendrick in 1908, and a few cars were loaded with coal from the Arvada bed. A company is now contemplating the sinking of a shaft near Kendrick. The plan is to sink deep enough to reach three or four coal beds and work them all from the same shaft. Development is being pushed by J. N. Sweat and J. W. Smith.

A small mine in the bank of Powder River, about half a mile south of Arvada, is the source of fuel supply for some of the people living near. This mine was opened in the winter of 1905 and several cars of coal were shipped. The coal was hauled to the railroad in wagons. Active mining continued only about five months, but the bank is kept open for the small supply which is obtained here each winter.

On the west side of Powder River, about 6 miles above Arvada, in the NW. i sec. 22, T. 53 N., R. 77 W., there is a prospect in the Felix bed, from which near-by ranchers get an occasional load of coal. There are other small prospects in this bed at other points on Powder River and Crazy Woman Creek, but they are little more than cleaned outcrops where a rancher or two has taken a few loads of coal.

Near the station at Croton an entry has been driven 120 feet on the Felix coal bed. Four or five carloads were shipped to Gillette in 1902, but since then no coal has been mined here, except by one or two ranchers living in the neighborhood.

At Echeta, where the Felix coal bed has a thickness of 30 feet, a company is now preparing to strip the coal. As the cover is thin it is planned to strip and quarry as long as the overburden is not too great. The relation of the coal bed to the railroad is such that it will be possible to build a level track from the bottom of the strip to the tipple at the railroad, one-fourth mile away. The manager of this company, P. J. Barr, was grading the track in the fall of 1908.

A small mine was opened in the creek bottom at Felix several years ago, and it is reported that coal was shipped by rail. The industry was short lived, however, and the only output now is an occasional

a nu:J. r. S. r.col. survey No. 341. 100!), pp. 135-136.

136 Contributions To Economic Geology, 1908, Part Ii.

load taken from prospects in the first draw north of Felix. The Felix coal bed is mined in a small way near Gillette by W. F. Vines and B. H. Barker. It sells in the village for $2.75 to $3 a ton.

A workable coal bed comes to the surface at Mintum. A prospect pit in the NW. i sec. 2, T. 49 N., R. 71 W., about 1 mile south of the railroad, is said to have gone down 18 feet in coal and not reached the bottom of the bed. A few loads are dug here each \vinter by neighboring ranchers.

Another source of fuel supply of local reputation is the Hulbert mine, situated about 9 miles north of Gillette, in the NE. i sec. 10, T. 51 N., R. 72 W. This is a bed 22 feet thick. An opening 15 feet wide extends probably 15 feet back into the hill. Eight feet of coal is left in the roof and from 6 to 7 feet of coal is mined. In spite of the distance some of this coal is hauled by wagon to Gillette.

Conclusion.

The production of coal in this field at present is limited practically to the small amounts taken by ranchers for their own use. The near future, however, is likely to see active mining of coal at various places along the railroad.

In 1900 the Chicago, Burlington and Quincy Railroad Company began a series of tests of the Sheridan coals in its locomotives and found that with specially constructed grates of large area and modified fire boxes and stacks the coal could be used successfully. Now all locomotives on the Wyoming division of this road are fired with Sheridan coal. As the Powder River coal field is the eastern continuation of the Sheridan field, and as the physical and chemical properties of the coal are practically the same, it is expected that the Powder River coal will prove equally efficient.

Experiments made by the United States Geological Survey show that subbituminous coal (such as that in the Powder River field) develops an efficiency 2.7 times greater with the gas producer and gas engine than when used in the common steam engine. In fact, the Powder River coals, when used in a gas producer and gas engine, will in all probability produce as much power per ton as the best West Virginia bituminous coals when used with a steam engine. With the further development of the producer and gas engine the mining of these low-grade coals should greatly increjise.

As the demand for coal increases, capital will be invested in the development of the large beds described in this report. With a railroad already built through the area, and the Powder River valley north of Arvada offering an abimdance of coal and an route for a new railroad, it may be expected that in a comparatively short time this portion of the great undeveloped region will be making a large addition to the annual coal production of Wyoming.

The Buffalo Coal Field, Avyoming.

By HoYT S. Gale and Carroll II. Wegemann.

Introduction.

The Buffalo coal field of Wyoming is part of a broad area of coalbearing strata in Wyoming, Montana, and the Dakotas, commonly known as the Northern Great Plains province. Certain fields or even local districts of this province have become more or less well known as coal-producing centers, but little authentic description of this great area has been available prior to the investigations that have been carried on by the United States Geological Survey in the last few years.

The examination of the Buffalo coal field in the sunmier of 1908 was a direct continuation of similar work that had been done in the preceding year by Joseph A. Taff in the Sheridan field, to the north. The Buffalo and Sheridan fields are also continuous with or a part of the extensive and valuable coal fields to the east and south . of them. A part of this province contiguous with the Buffalo and Sheridan fields, including an area reaching eastward from the vicinity of Clearmont along the route of the Chicago, Burlington and Quincy Railroad, was examined in 1908 by R. W. Stone and C. T. Lupton, whose work forms the subject of the preceding paper in this volume.

The field party in the Buffalo area included, besides the authors, Doane Gardiner, temporary field assistant, who measured many of the detailed hand-level sections given on Plate IX, Alcott F. Elwell, and W. H. Beekly.

Topography.

Relief.

The topography of the Buffalo field may be described in a very general way as that of more or less typical plains, although in detail it presents a- variety of types and features which are in many places sharply contrasted. Ck)|igidered broadly, it comprises portions of the foothill province of the Bighorn Mountains or front range of northern Wyoming ai:i4 the extreme outer margin of the Great Plains area that stitches between the Bighorns and the Black

138 Contributions To Economic Geology, 1908, Part It.

Hills. The area included in the coal field proper belongs both geographically and geologically to the plains province.

In a broad way the plains in this area exhibit two general types of topography. Along the foot of the mountains there is a belt characterized by broadly rolling and smoothly rounded slopes, largely covered with surficial deposits of sand, gravel, and bowlders, the surface of which is usually grass covered. Contrasted with these smooth grassy plains are the hills,'' which occupy a more extensive territory to the east and northeast, and which through the intricate systems of dissection and erosion slopes developed upon them merge into the most rugged badland forms. Each of these types may be again subdivided into two more or less distinct classes, so that the topography of the field as a whole may be described under four fairly comprehensive headings, as follows, the arrangement being the order of their position with respect to the mountains: Foothills and upper terraces; smooth grass-covered plains and lower terraces; red hills; badlands.

Skirting the foothills of the Bighorn Mountains and extending down the valleys of the principal streams that head wdthin the mountains is a series of remarkably well-developed gravel-covered terraces. Some of them form broad alluvial plains for a distance of 5 to 10 miles from the mountains, but beyond these plains they are confined to the larger stream valleys, which tiiey follow for great distances. In some places four or five of these gravel-covered terraces may be observed from one point, rising one above another. The slope of their surfaces away from the mountains is usually pronounced. The gravel cap is composed of rounded stream material wliicli varies in size from small to fair-sized bowlders and whose constituents represent most of the igneous and sedimentary rocks exposed in the mountains near from which they were derived.

The mantle of sand and gravel on these surfaces is not heavy, a fair estimate being perhaps 5 to 10 feet on the stream terraces. Nearer the mountains the gravel is thicker, but probably its thickness does not exceed 40 or 50 feet in most places. On the surface the gravel has been concentrated by subaerial erosion into a layer 6 to 10 inches thick, forming a protecting cap to the terrace which tends to check its further degradation. This feature is well represented along Crazy Woman Creek near Trabing, where the gravel terraces form a line of low hills along the stream valley, the country back of them, which is covered by a thinner mantle of gravel, having been reduced to a somewhat lower level. Unmistakable glacial polishing was observed on bowlders included in some of these deposits. One locality in which the glacial pebbles were found is cm a broad terrace 1 mile north of Buffalo, in the SW. sec. 23, T. 51 N., R. 82 W.

Buffalo Coal Field, Wyoming. 139

Between the terraces and the red hills to the northeast is an area of gentle slopes and broad, open valleys. At certain points remnants of terrace gravel occur within this area, and it seems not unlikely that at one time the greater part of it was covered by this deposit. Three miles southeast of Buffalo an extension of the terrace area forms the divide between Clear Creek and Dry Creek, and, as it were, bridges the gap between the terraces and the red hills.

In sharp contrast with the broad, grassy slopes described in the preceding paragraphs is the region of more rugged topography, made conspicuous by its red-capped summits and slag-covered slopes. As mentioned in the discussion of structure (p. 147), the baked rock formed by the burning of the Ulm group of coal beds ceases along a line which crosses the field from northwest to southeast in the line of the general strike of the beds. (See PI. X.) The area of burned coal is not over 12 or 15 miles in width from northeast to southwest. It follows in general the trend of the mountains. On the northeast the slag has been removed by erosion and the boundary of the red hills is most irregular.

The topography of the red hills is in places very rugged. The beds of baked sandstone and shale resist the agencies of erosion and so form the cap rock of most of the hills. Below the protecting cap the slope of the softer rocks tends to remain steep. The slag beds are almost horizontal over most of the area, so that hills capped by the same bed are of nearly equal altitude. The topography thus developed is that of flat-topped mesas separated by canyon-like valleys. Where erosion has progressed further the mesas are reduced to cones and the valleys are broadened. The baked rock is of many shades of red, brown, and purple, the colors being due to the oxidation of the iron in the rocks by the heat of the burning coal. The contrast between the yellow sandstone and shale of the slopes and the brilliant red rock of the crests of the hills is most striking and enlivens a landscape in many ways dull and unattractive.

Badlands of the usual type occupy the territory of lower altitude to the northeast of the red hills. Here the coals have not burned to any great extent and the topography is not influenced by heavy beds of baked rock. Flat uplands exist at localities which are determined by the presence of thin beds of limestone that form the more resistant layers and prevent the erosion of underlying beds, but the topography is for the most part one of minute dissection. Sharp-crested ridges alternate with steep, narrow valleys. There is no water except that of a few miry springs that seep from the coal beds and what is left in depressions of the coulee bottoms after torrential rains. The slopes of the hills are covered with patches of sagebrush and scanty buffalo grass or are entirely bare. Travel over such an area is often exceedingly difficult.

140 Contributions To Economic Geology, 1908, Part Ii.

Drainage.

The drainage system which carries off the surplus water of the Buffalo field includes two important tributaries of upper Powder River — Crazy Woman and Clear creeks, both formerly referred to as "forks'' of Powder River proper. Each of these streams is in turn fed by numerous branches of various sizes. Piney Creek, a fork of Clear Creek, is equal in size to that stream, so that the perennial streams of the field are really three in number.

The water in Crazy Woman Creek is somewhat alkaline, but that of Piney Creek and Clear Creek is remarkable} pure, being derived directly from the wooded slopes and snow-capped peaks of the Bighorn Mountains. All the other streams of the area are of intermittent character.

Lake De Smet is a body of water about 3 miles in length by a mile in width, lying in the western part of T. 52 N., R. 82 W. Its long axis is approximately parallel to the strike of the rocks in this region, about N. 45° W. The lake has no outlet. At its north end it receives a small stream known as Shell Creek, which flows across a broad, flat meadow almost as wide as the lake itself. A narrow valley to the north connects this flat with the flood plain of Piney Creek. It is stated by General Carrington® that in 1866 Shell Creek flowed through this valley and emptied into Piney Creek, the lake having at that time no inlet. At the southeastern extremity of the lake a broad valley may be followed into that of Boxelder Creek.

The Buffalo region is one of comparatively scant precipitation, and away from the foot of the mountains springs are rather rare. The most common are small seeps along the channels of dry or intermittent stream courses. Many of these probably represent the underflow of the valley, a part of which may be brought to the surface by a barrier of some sort or by a relative shallowing of the detritus zone in which it flows. Such waters occurring in the area of comparatively less consolidated Fort Union (Tertiary) strata are in general rather heavily charged with alkaline salts, as are the soils over which they pass.

Springs of another type are locally somewhat common and many of them afford good water. These usually occur along the outcrops of coal beds and, like the underflow currents, are most common along stream channels or in valley bottoms, the most favorable points for water to reach the surface. The coal beds arc the best water-bearing strata of the Fort Union C*De Smet") formation, the others being relatively impervious clays and clayey layers. Their waters are fre-

oCarrlngton, II. B., Alwaraka, land of massacre, 1878, p. 142. "The water is deep and Intensely alkaline and there is neither inlet nor outlet, as the little creek which is crossed iK'fore reaching the lake passes by the west end at a few hundred yards distance and turns westward to the Piney Forks, emptying Its stream their junction."

Buffalo Coal Field, Wyoming. 141

quently charged with iron and sulphur compounds and sometimes with alkaline salts, but usually not to a very objectionable degree. These springs are so numerous within the coal field that it may fairly be assumed that a spring is a good indication of a coal bed, although the coal itself may be concealed by alluvial wash.

Stratigraphy. Introduction.

So far as the older sedimentary formations are concerned, the general stratigraphy of this field has already been discussed at length in the reports by Darton and others. In the present review of the Mesozoic and later rocks, however, some modification of the stratigraphic classification used in former reports is now required, to conform to more recent geologic and paleontologic information.

The vicinity of Buffalo does not offer very favorable opportimities for the study of the Cretaceous and older rocks in the foothill region of the Bighorn Mountains. The rocks on the east flank of the range are steeply tilted and the structure is complicated by faults that tend to obscure the normal relations of the strata. The chief difficulty is, however, that the extensive outwash deposits of bowlders and gravel along the base of the mountains have largely obscured the underlying rocks and only fragmentfiCry information concerning them can be obtained.

Pre-Tertury Rocks.

Of the several formations into which the Cretaceous rocks of this region are divisible, only the upper one, to which Darton has given the name Piney formation, contains coal in commercial quantities. For that reason the other Cretaceous formations will not be considered in this report.

Piney Formation.

The name Piney was used by Darton to designate ''the lowest formation of the thick series of fresh-water sandstones and shales of later Cretaceous age formerly designated Laramie ' lying in the great basin adjoining the Bighorn uplift.'' It embraces all the rocks between the Parkman sandstone below and the Kingsbury conglomerate member of the Fort Union above, or, in the absence of the Kingsbury conglomerate, between the Parkman below and the *'De Smet'' (now referred to Fort Union) above. Whether the rocks thus described are a formational unit as Darton considered them, or should

a Darton, N. H., Geology and underground water resotircos of theceninil I'lains: Prof. Taper I'. S. Oeol. Survey No. 32, 1905; (ieology of the liignom Mountains. Trof. Paper U. S. Geol. Survey No. 51, 1906. Cloud Peak-Fort McKlnney folio (No. 142), Geol. Atlas V. S., U. S. Geol. Survey,

6 Darton, N. H., Geology of the Bighorn Mountains: Prof. Paper U. S. Geol. Survey No. 51, 1906, p. 59.

142 Contributions To Economic Geology, 1908, Part Ii.

be referred as a whole or in part to the Fort Union, is now an open question. On account of lack of more positive evidence on the subject the name Piney is here retained as originally used.

As described by Darton the Piney formation southeast of Buffalo is about 2,000 feet thick.

The lowest beds are sandstones and shales of light color, and the upper members consist of white, red, and green sands and sandstones alternating with layers of green and yellow clays, dark shales, and iron concretions, the latter composed of sand cemented by iron oxide. This formation is extensively exposed along the north side of Rock Creek southwest of Lake De Smet, also on the west slope of the high ridge south- of Johnson Creek, and notably in the slopes a mile southeast of T. A. ranch, where it forms badlands.

About 9 miles southeast of the T. A. ranch and 4 to 5 miles southwest of Trabing, in the western part of T. 47 N., R. 81 W., the upper portion of the Piney formation, together with the overlying Fort Union (*'De Smet'*) formation, is well exposed. Near the top of the formation are several thin beds of coarse sandstone which breaks into sharp angular blocks. Associated with these sandstones are beds of pink shale. The underlying strata are dark-brown and drab shales containing numerous beds of coal, several of which are of economic importance. Here and there shale of a greenish cast may be noted. Coarse, friable sandstone also occurs and there are numerous thin beds of blue limestone which weathers to dark reior brown. Shale grades into sandstone and sandstone into shale, vertically and horizontally. It is rare to find an individual bed which can be traced for any great distance. The coal beds form one exception to this statement, for, although varying in thickness and quality, many of them extend over considerable areas.

Near Buffalo no coal beds of importance are known in this formation, south of Crazy Woman Creek coal is mined at various points in T. 44 N., R. 81 W.; T. 43 N., R. 79 W.; and T. 42 N., R. 77 W., in beds which probably correspond to those near Buffalo. Although this upper portion of the Piney formation resembles in many ways the somber-colored shale which underlies the typical Fort Union in the vicinity of Miles City, Mont., there is some doubt as to its exact correlation.

In T. 43 N., R. 79 W. (see PI. XI) the rocks underlying the typical Fort Union come to the surface along the flank of a broad dome drained by Salt Creek. The northeastern portion of the township is covered by the tine-grained buff sandstones and shales of the lower portion of the Fort Union, which is here barren of coal beds. This sandy piiase passes into darker shale below without any sharp line of contact between the two formations. The shale is approximately (300 feet thick. It is of various shades of gray, some layers

a hix\ cit.

Buffalo Coal Field, Wyoming. 143

being nearly black and others almost white. In its upper part are several pinkish beds. About 300 feet below the top are two beds of coal to be described later. Numerous thin beds of blue limestone which weather to a dark-red color occur, especially near the base of the shale and in the imderlying sandstone. This sandstone, about 500 feet in thickness, forms a very prominent pine-covered ridge. It is for the most part bluish white in color and fine grained.

Below the sandstone is a mass of shale with thin sandstone and limestone beds and below this a white sandstone which forms a less prominent ridge than the one just described. In the shale valley between these two ridges some plant fragments were collected which, although they are not sufficient for a definite determination, are said by F. H. Knowlton to have decided Fort Union affinities. Below the lower of the sandstone beds is a great thickness of beds of alternating sandstone and shale with a few thin limestone layers. Dinosaur remains, including the frill bone of a TriceraiopSy were found in this formation in the NW. i sec. 4, T. 42 N., R. 79 W. It would seem, therefore, that these beds may represent a formation in eastern Wyoming and Montana which has been called by various names, "Lance Creek beds,*' Ceratops beds," ''Hell Creek beds,'* etc.

Bamum Brown, in an article on the Hell Creek beds " of Montana,** described a series of lignite-bearing beds below the typical Fort Union and above the Hell Creek beds.'' It is possible that the darkcolored shale which conformably underlies the Fort Union in the township under discussion may represent this same lignite-bearing formation. If so it is doubtful whether the sandstone ridges belong with the upper shale or with the Ceratops-hesLving beds below. In passing northward along the base of the mountains the sandstone ridges become less and less conspicuous until they seem to give place to shale and are not observed as sandstone in the exposures west of Trabing.

Numerous plant fragments and some imperfectly preserved leaves were found in the beds underlying the Kingsbury conglomerate member, but unfortunately these were not adequate for a positive age determination.

Tbrtury Rocks. Fokt Union C*De Smet") Formation.

The Kingsbury conglomerate member of the Fort Union formation is one of the most conspicuous and prominently exposed rock divisions in the Buffalo region. It takes its name from Kingsbury Ridge, a prominent topographic feature about 6 miles southwest of Buffalo,

a The Hell Creek beds of Montana: Bull. Am. Mus. Nat. Hist., vol. 23, 1907, p. 834.

144 Contributions To Economic Geology, 1908, Part Ii.

near the Klondike-Hazleton road. Here it is characteristically exposed and probably attains its maximum thickness. It is also well exposed on Rock Creek, northeast of Buffalo, and still farther north beyond the area covered by this report. Darton treated it as an independent formation, although he stated that it was probably developed out of the ''De Smet" formation. That the conglomerate is a member of the Fort Union formation there seems no longer any doubt, and it will be so treated in this report.

The conglomerate is composed of water-rounded gravel and bowlders, derived from the older sedimentary rocks of the adjacent mountain range and including also specimens of the granitic core of the range. So far as observed none of the basic dike rocks from that region are to be found in these beds. Among the pebbles identified are coarse red or gray granite; flat pebbles characteristic of the Deadwood (Cambrian) formation; brecciated and weather-pitted fragments or pebbles of the Bighorn (Ordovician) limestone; massive, crystalline rock of the Madison (Mississippian) limestone, containing numerous crinoids and spirifers; and other limestones, sandstones, and shales of the later formations, which are not so clearly identifiable as those of the older rocks. These pebbles are cemented in a coarse sandy matrix, and seem in their present state to have been laid down in channel deposits of exceedingly irregular bedding. The conglomeratic strata, which are in many places thick and massive, are interstratified with finer-grained, more uniformly bedded layers of sandstone and shale, dull greenish gray or drab in color, much resembling the rocks of the underlying somber-colored beds. In many places the conglomerate, even where forming prominent ledges, constitutes but a fractional part of the actual strata represented, the coarse debris resulting from its disintegration covering and concealing the softer beds.

The Kingsbury conglomerate member is evidently a shore, delta, or alluvial-fan deposit. It is clearly unconformable with the underlying formations, as its outcrop transgresses obliquely across them and its dip is somewhat discordant with that of the adjacent beds. Its deposition, therefore, appears to have followed or to have marked the culmination of a period of uplift and denudation at this particular locality and is tliought to represent the erosional activity awakened at one of the more important stages of uplift of the Bighorn Mountains. Tlie transition from the Kingsbury conglomerate to the finer sediments overlying it is by no means an abrupt one. Ijocal beds of conglomerate, apparently of lenticular form, occur throughout a considerable thickness of strata, perhaps even thousands of feet above the main conglomerate mass.

To the north and also to the soutli the Kingsbury conglomerate member lingers out and disappears and the normal Fort Union C'De

Buffalo Coal Field, Wyoming. 145

Smet strata succeed the dark shale of the Finey formation without sign of break between them. The Fort Union age of the Kingsbury conglomerate now seems very well determined by stratigraphic and paleontologic evidence.

The shale and sandstone of the Fort Union CDe Smef ) formation are prevailingly light yellow in tone, in more or less decided contrast to the dark shale of the Piney below. However, somber-colored shale occurs in the Fort Union at many localities, especially in association with coal beds, and in places it is necessary to examine a considerable exposure to distinguish the two formations. The Fort Union consists for the most part of shale and line-grained sandstone, alternating here and there with thinner beds of calcareous sandstone that are commonly fossil bearing. Most of the valuable coal beds of the Buffalo region occur in the Fort Union C*De Smef ) formation.

In the immediate vicinity of Buffalo, as already stated, the shale and sandy beds interstratified with the Kingsbury conglomerate member are of a dull-greenish cast, weathering to a drab or even yellowish clay or sand when dry. They are thus indistinguishable in appearance from much of the imderlying Piney formation, but, as a rule, the Fort Union does not present the peculiar banded appearance, due to the alternation of light and dark shales, so characteristic of the Piney formation. Of these duller-colored strata of the Fort Union, there is a rather imcertain thickness below the principal coal-bearing group. An estimate based on observations along a section extending from Rock Creek to a point near Lake De Smet seems to indicate that there are about 2,000 feet of beds above the Kingsbury conglomerate member and below the lowest important coal of the Ulm coal group, as represented at the local coal banks or mines at the southwest side of the lake.

The coal-bearing portion of the Fort Union in the Buffalo region includes the upper 600 or 800 feet of the section as represented in the detailed stratigraphic sections inade during the present investigation and published in this report. The coal is described in detail on pages

Sihcified trees are of common occurrence in association with the coal-bearing beds. They afford evidence of the climatic conditions and indicate rapidity of deposition during the period in which they and the coal beds were laid down.

The occurrence of surficial deposits of sand and gravel that cover the terraces along the base of the mountains has been noted under the heading Topography. These deposits occupy very consider-

Stanton, T.W.," Cct-o/op* beds" of Wyoming and Montana: Proc. Washington Acad. Scl.. vol. 2, No. 4, 1900, pp. 2C8. Knovrlton, F. H., Stratigraphic relations and paleontology of the "Hell Creek beds,'' " Ceratop$ beds," and equivalents, and their reference to the Fort Union formation: Proc. Washington Acad. Scl., VOL 2, No. 3, IflOB, pp. a09, 212.

7963**— BuJl 3aX— 10 10

146 Contributions To Economic Geology, 1908, Part Ii.

able areas in the Buffalo field, and in many places mask the underlying rock formations continuously for miles, practically preventing any direct study of the bed-rock structure or strata.

Rock Structure.

The rock structiu-e of the Buffalo coal field is comparatively simple. The strata of the plains are practically horizontal or have dips so low that they are in places difficult to detect. Along the eastern flank of the Bighorn Range, however, the coal-bearing strata are upturned sharply, their outcrops occupying a comparatively narrow strip of territory along the base of the mountains. To a large extent details of the major structure are concealed by the outwash deposits of gravel and sand along the mountain foot. The structure where revealed, however, shows the fold to be fairly uniform, but broken here and there by faults of considerable extent. With the older, more sharply folded strata this report has little to do, for tlie coals are confined to the younger and relatively flat-lying rocks of the plains. The dips in the later formations are generally slight, but are important, as bearing on the extent and position of the valuable coals.

By a comparison of accurately determined altitudes, based on United States Geological Survey bench marks, of certain coal beds along Clear Creek between the mouth of Piney Creek and Buffalo, the dip of the rocks to the northeast is foimd to average but a fraction of a degree. This dip is far too slight to be recognized in any particular locality or outcrop, and is obscured by the creep of rocks on many of the steep slopes. On the east side of Lake De Smet the dip is too slight to be observed, but at the coal bank on the southwest side of the lake the beds dip 4° away from the mountains, with a strike of N. 45° W. The dip increases toward the southwest, and near the comer of the township it is 25°. In sec. 3 of the township west of Lake De Smet a dip of 10° was observed, the strike being the same as that near the lake. Along the western shore of the lake, especially near the north end, occur several parallel ridges of slag, which correspond in direction with the strike of the beds. These ridges apparently represent the outcrop of coal beds at the Healy horizon, and the straight course and narrowness of the band of slag seems to indicate tliat the beds at this place dip more or less. No slag occurs southwest of this locality. The coal beds below the Healy do not, as a rule, form noticeable slag.

An inspection of the map will show that a line drawn along the southwest side of Lake De Smet and ])arallel to its long axis corresponds to tlie strike of the rocks in that locality, and if continued southeastward to the southern border of T. 50 X., R. 81 W., in general marks the western limit of the burned area. From that point on, the boundary of the slag swings a little more to the eastward, north of

Buffalo Coal. Field, Wyoming. 147

the Bilderbach Lakes. These facts may be significant of a structure that has not yet been determined from the observed bed-rock exposures.

Southeast of the Clear Creek valley at BuflFalo, in sees. 16, 21, 22, and 27, T. 50 N., R. 81 W., several parallel ridges of slag similar to those near Lake De Smet mark the limit of the burned area. They are approximately on the line of strike of the beds at Lake De Smet. Slags from several different coal horizons are here so intermingled that it is difficult to make accurate determinations of the amount of the dip or the identity of the individual beds. The dip, if any, is but slight. A mile to the west, in sec. 18, a dip of 1® NE. was observed on a bed of carbonaceous ale. West of this point the observed dips are low for about 6 miles, but in sec. 30, T. 50 N., R. 82 W., the beds are upturned sharply and within a mile stand almost vertical.

Southeast of Lake De Smet, in sec. 2, T. 51 N., R. 82 W., a dip of 10° 20' was observed in a coal bed taken as representing the Walters coal. From that point for some distance southeastward the slag beds are so confused that no dip determinations could be made. Just east of Buffalo there appears to be a gently folded syncline, for in the Munkre and Mitchell mines the coal beds dip at low angles to the southwest, while at Buffalo and north of Buffalo the dips are to the east. About miles east of Buffalo the slags of the Healy and higher coal beds cease in a rather abrupt escarpment, but no marked dip was observed there.

In sees. 17, 20, and 29, T. 49 N., R. 80 W., occur two shallow ponds. Each depression is opposite a small tributary of Crazy Woman Creek and is separated from the Crazy Woman Creek drainage basin by a very low divide. In sec. 8 the rocks dip to the northwest and in sec. 21 to the east. There appears to be a low anticline just east of the lakes, its axis trending about north and south. The lakes themselves seem to occupy the former heads of the two valleys above mentioned, as if the drainage had been interrupted by the warping of the strata after the valleys were formed. In the township west of the lakes the dips are low and the surface so covered that but little is revealed of the structure.

Along Crazy Woman Creek at intervals for 25 miles below Trabing a coal known as the Dry Creek bed outcrops at water level, showing that the dip of the rocks to the northeast, although locally undulating, is on the average equivalent to the fall of the stream. Five miles west of Trabing, however, the base of the Fort Union is brought to the surface and the underlying dark shale of the Piney formation is exposed, showing a dip of 12°. The ridge formed by the upturn of the strata can be seen extending outside of the area studied. To the south it traverses T. 47 N., R. 81 W., with a strike of N. 27° W.

148 Contributions To Economic Geology, 1908, Part H.

and dips of 6° to 8°. The ridge is formed chiefly by portions of the Piney formation. It appears to extend continuously southward to Powder River, which it crosses below the mouth of South Fork. From that point it tiuns somewhat toward the east, crossing the southern portion of T..43 N., R. 79 W., and continumg southeastward along the periphery of a broad dome or anticline which occupies the general region drained by Salt Creek.

The Coal.. Quality And Physical Properties.

The coal of the Buffalo field should probably be classed as subbituminous, although in character it is not far removed from lignite. It differs from lignite in color, texture, and calorific value. Its color is dark brown or even black, in contrast to the more woody brown of lignite. Although the original grain of the wood is to be observed in much of the coal, the cellular structure is not so distinct as in lignite and in some beds or parts of beds is lacking entirely. The coal is more brittle than lignite, breaking with a conchoidal fracture. Its calorific value averages about 10,000 British thermal units; this is somewhat in excess of that of the lignite of North Dakota, which averages only about 8,400 British thermal units. It may be observed that the more woody layers of the coal, dark brown when first mined, quickly blacken on exposure and appear to lose much of their woody texture. The coal in this dried condition is brittle and, when freshly broken, lustrous black in color. It breaks as readily across the grain of the original wood as it does parallel to it. On continued exposure, however, the coal loses its luster and finally crumbles or ''slacks" to a fine powder.

Small masses of resin are embedded in the coal at many places and it is reported that some of them are several inches in diameter. From this occurrence of resin and the amount of coal that shows evidence of woody structure it seems probable that the greater proportion of this coal was formed from tree trunks rather than from the finer deposits of a bog. The occurrence of silicified logs and tree stumps in many of the beds helps to substantiate this view. The logs are embedded in the coal, mostly in horizontal positions. In some cases it is evident that part of the log was changed to coal while otlier parts were silicified. The occurrence of petrified logs is not at all uncommon in the sandstone and shale above the coal beds. Some trunks of trees are standing in their original positions half covered by coarse sandstone formed from the sand which originally buried them. They range in diameter from a few inches to 3 or 4 feet.

BtJFFALO COAL FIELD, WYOMIKO. 140

The coal beds of this field range from thm seams of only a few inches to heavy beds over 30 feet thick. The thickness of some of the beds is comparatively constant over broad areas; that of others varies widely. However constant in thickness a bed may be over a large area, it is evident that toward the limits of the ancient marsh in which the coal was formed tlie coal must be expected to change in thickness and quality and finally to end entirely.

The various beds of coal in the section differ in quality as well as in extent and continuity. A coal clean at one point may be continuous with and merge into a bony coal or carbonaceous shale which is worthless, this difference being due apparently to a difference of conditions in the marsh at the time of formation of the coal, changes in the character of vegetation, the introduction of foreign matter by water currents, etc. In certain places along the outcrop of a coal bed is observed a thin parting of shale, which thickens in passing along the strike, separating the coal bed into benches in such a manner as to render worthless a bed that in other localities is valuable.

Although a coal bed may change greatly in character from place to place, as has been observed, its horizon may usually be recognized and the interval between it and the next important bed above or below may be determined. In many cases this interval seems to be constant and may be used in identifying beds in different portions of the field. The constancy of such an interval is probably the result of the uniform rise or fall of water level with respect to a low-lying land surface over a wide territory and the consequent uniform horizontal distribution of the material laid down below and filled up to the temporarily estabUshed water level.

Chemical Analyses.

Owing to the location of this field at a distance from lines of transportation there is little demand for its coal and only a few mines have been opened to supply fuel for local consumption. On account of the scarcity of working mines it was impossible to procure many samples of coal for analysis. In the following table are given the analyses of the samples that were collected, followed by a description of the location and the conditions at the time of collection. Each sample was obtained by cutting a channel across the coal bed or the particular bench of coal to be sampled, and pulverizing and quartering the coal thus' procured. The samples were sent to the chemical laboratory in sealed galvanized-iron cans.

150 CONTRIBUTIONS TO fiCONoMlO GfiOLOdlf, 1908, PART tt.

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6469 (PL X, 18). From the bench above the one at present worked in the Mitchell mine. The upper part of this bench is 1 foot SJ inches thick, the lower part 2 feet 8 inches; the two parts are separated by 2 inches of bone, which was not included in the sample. The sample was taken from the wall of the slope near its foot. The coal had been exposed to the air of the mine for some months, but as there was considerable moisture present the face of the bed was as firm as when freshly mined. About 3 inches of the face was removed before the sample was cut. The cover above the coal at this point is about 100 feet thick and consists in great part of coal and coaly shale beds.

6470 (PI. X, 18). From the bench at present worked in the Mitchell mine. This bench consists of four parts whose thicknesses, in descending order, are 3 feetSinches, 11 inches, 7 inches, and 1 foot 8 inches. The thin shale partings between them were thrown out in taking the sample, which was cut about 20 feet north of the foot of the slope. The mine had been opened the year before, but coal had been mined at this particular place only a few days before the sample was taken. The face of the coal showed no sign of weathering and no moisture was seen at this place. It is believed that the coal was practically unweathered. There is about 120 feet of cover above the coal.

6410 (PI. X, 19). From the bench at present worked in the Munkre mine. The coal bed is 6 feet thick and carries a thin bone parting in some parts of the mine. This is an old mine, but the sample was obtained from a face of coal which has been worked recently about 200 feet from the foot of the slope. There is about 85 feet of cover at this point, consisting of shale and coal beds with a little alluvium at the surface. No moisture was to be seen and it is believed that the coal was practically unweathered.

6434 (PI. X, 9). Represents an upper bench, 2 feet 6 J inches thick, of a coal bed exposed in the bank of a coulee from which coal is obtained for local use. This coal is under about 8 feet of cover, which is for the most part alluvium. Coal from this place had been mined on the day before the sample was taken, but the face of the coal had already begun to check. About 3 inches of the surface was removed before the sample was takn. Although the coal appeared hard and bright, it seems probable that changes had taken place in it due to long exposure to surface conditions. This description applies also to sample 6435.

6435 (PI. X, 9). From lower part of same bed as sample 6434. Several thin shale partings are present, as shown on Plate X. These were thrown out and the sample was obtained from the three parts of the bench, 1 foot 7 inches, 11 inches, and 1 foot in thirkneps.

Burning Of Outcrop.

Certain of the coal beds of the Buffalo field have burned extensively along their outcrops, baking and partly melting the rocks above them. These baked rocks are of various shades of pink, brown, red, and even purple, and form one of the most conspicuous features of the landscape. Being hardened by the heat, they resist erosion much more eflfectively than the unaltered soft sandstone and shale, and thus form the capping rock of many of the hills. In certain localities coal beds are at present on fire, and the phenomena of the burning, the settling of the overlying beds, and the formation of fissures may be observed in actual process of development. It seems probable that the beds take fire by spontaneous combustion. Such firing of piles of slack of subbituminous coal is of common occurrence. In nature the undercutting of coal banks by streams and the consequent camg of the

152 Contribution'S To Economic Geology, 1908, Part 11.

coal furnishes similar slack piles, and it is not unreasonable to suppose that they take fire in a similar manner.

It should be remarked, however, that certain beds seem to have burned much more extensively than others. The Fort Union coals of the Buffalo field (the Ulm coal group as defined by TaflF**) form marked areas of slag, but the coal beds of the Intermediate coal group, which being lower in the section are exposed farther to the northeast, are not burned to any considerable extent. The lowest coals of the Fort Union, which have been termed by TaflF the Tongue River coal group, are widely burned. The coals of the underlying somber-colored shale have burned but little. All these coals are subject to practically the same conditions of climate and erosion and it seems probable that the differences in the amount of burning are due to slight differences in composition that render some more prone to spontaneous combustion than others.

Many facts are difficult of explanation, however. For example, the Healy coal is universally burned along its outcrop over broad areas to the northwest of Crazy Woman Creek, but southeast of that stream, although the same coal bed is present, it is very little burned, the creek marking the boundary between the burned and unbumed areas.

Correlation With Other Fields.

As already mentioned, the coal beds of the Buffalo field belong to the group designated by Taff in the field to the north the Ulm coal group. They occur in the upper portion of the Fort Union formation. Theoretically the coals of the Intermediate and Tongue River coal groups, as defined by Taff and exposed in the fields to the east and north of Buffalo, if continuous should underlie this area. Along the base of the Bighorn Mountains the flat-lying strata of the plains- are tilted slightly eastward, so that in approaching the mountains one passes across the edges of the upturned beds. It is significant that no outcrops of coal beds much below the Ulm coal group can be found in this area except in one place west of Trabing, where coals at the base of the Fort Union are brought to the surface. The margins or shores of the ancient marshes in which the coals are supposed to have been formed })robably lay somewhere along the base of these mountains, and along these lines the vegetal deposits would therefore cease. In the absence of more positive data as to the extent and character of coal beds lower in the section it seems impossible to make definite statements concerning any beds than those exposed at the surface within this area.

oTafl, J. A., The Sheridan coal flekl, Wyoming: Bull. U. S. (Jeol. Survey No. 341. 1909, pp. 123-250.

BtJFALO COAL FIELD, WYOMING. 153

Important Coal Beds Of The Buffalo Field.

There are, to speak generally, three horizons at which coal occurs throughout the Buffalo field. The lowest coal is termed for convenience the Dry Creek bed, from its occurrence along that stream. About 130 feet above this bed is the coal that is mined near the Healy ranch, which is referred to in this report as the Healy coal (d). In some parts of the field there are at this horizon two workable beds with an interval of 50 or 60 feet between them. About 175 feet above the Healy horizon is a thick coal bed workable in some portions of the field, which has been mined to a small extent in the NE. sec. 16, T. 52 N., R. 81 W., for use at the Walters ranch on Clear Creek, and which is here termed the Walters coal. Other beds occur at intermediate horizons and are locally important. There are also remnants of higher coal beds preserved in some parts of the field.

Description By Townships.

In describing the coals of tlie Buffalo field the area will be considered by townships, beginning at the northeast corner and going from east to west across the field, each tier of townships being discussed in order from north to south.

jT. 53 N,, B. 79 W. — The principal coal bed within this township is the Healy, which occurs at an elevation of about 4,400 feet above sea level. The bed has been removed by erosion over tlie larger portion of the township. Its remnants appear principally iilong the divide between Clear and Crazy Woman creeks. In many places, especially where the coal has been left in small patches upon hilltops, it has burned, forming a marked slag. Near the west side of sec. 20 a detailed section (No. 8) was made that shows the bed to be 18 feet 6 inches thick counting the included shale partings.

About 40 feet below this bed occurs another coal that is usually over 3 feet tliick. The outcrops of the two as represented on the map are practically identical, although the endeavor has been made to map the upper bed only. In the strata from 100 to 200 feet below these coals are several thin beds of coal and carbonaceous shale, none of which are known to be over 2 feet 6 inches thick and none of which form noticeable slag by burning, (hhy ii.)

Practically nothing is positively known concerning other valuable coals that doubtless occur in the strata below water level in this area.

a Letters in parentheses refer to section.s on Plate IX.

Numbers in parentheses refer to sections of coal Ixds on Plates X and XI.

154 CONTRiBtJTIONS TO ECONOMIC GEOLOGY, 1908, PABT M.

Sections On Plate Ix.

a. Sec. 24, T. 50 N., R. 81 W. Section starts at coal in bed of Dry Creek and extends to hills on the east.

h. Sees. 13 and 14, T. 51 N., R. 82 W. Section starts at the burning coal bed in SE. i sec. 14.

c. Sec. 25, T. 51 N., R. 81 W. Section extends from coal exposed in dry stream bed to slag-capped hill on the east.

d. Sees. 9 ana 14, T. 51 N., R. 81 W. The lowest coal shown is that reported in the well at the Healy ranch in sec. 9. Its quality is unknown. The second coal is that opened at the Healy mine in sec. 14.

e. Sec. 8, T. 51 N., R. 81 W. Section starts from bench mark 4395 at gate of Healy ranch.

/. NE. SW. sec. 3, T. 51 N., R. 81 W., and southeast into sec. 10. Section begins at level of Clear Creek.

g. Sec. 32, T. 51 N., R. 80 W. Section starts at coal in creek bank and extends southeast to slag-capped butte.

h, NE. 1 NE. sec. 12, T. 52 N., R. 82 W. Section starts at level of Boxelder Creek.

i. NW. NE. i sec. 10, T. 52 N., R. 82 W.

;. NW. sec. 8, T. 52 N., R. 82 W. Section begins at water level of Ike De Smet and extends to peak west of Kennedy ranch.

h, SE. i sec. 3, T. 52 N., R. 82 W. Section starts at an opening on a coal taken to represent the Healy bed and extends to a hill one-fourth mile to the northwest.

7. Sec. 36, T. 52 N., R. 81 W. Section starts at opening on Healy coal, m. Sees. 2G and 35, T. 52 N., R. 81 W. Section starts at creek level.

n. Sec. 24, T. 52 N., R. 81 W. Below C. N. Walters ranch on Clear Creek. Section starts at creek level.

o. Sec. 24, T. 52 N., R. 81 W. About 1 mile above Watts ranch on the east side of Clear Creek. Section starts at creek level.

p. Sec. 12, T. 52 N., R. 81 W. Section begins at water level on Clear Creek, half a mile above Copp ranch.

q, NE. sec. 1, T. 52 N., R. 81 W. The lowest coal shown is 10 feet above water level of Clear Creek below Copp ranch.

r. See. 35, T. 52 N ., R. 80 W. The heavy coal is that about GO feet above the Healy bed. The slag represents the "upper coal."

8. T. 52 N., R. 80 W. A general pcction for the eastern portion of the township. The thickest coal ehown outcrops in sec. 3; the higher coals were noted in sec. 23.

t. Sec. 13, T. 52 N., R. 80 W. Section extends from the coal at Rattlesnake Springs to the slag capping the butte to the northwest.

u. T. 52 N., R. 79 W. A composite section for the western portion of the township. The highest coal shown cx'curs in the hill on the east side of sec. 18.

V. Sees. 3 and 24, T. 52 N., R. 79 W. A barometer section. "The lowest coal shown is at creek level in sec. 30 of the township east.

w. NE. sec. 33, T. 53 N., R. 82 W. Section extends from creek level below the old Senff ranch to the peak above the road.

X. Sec. 27, T. 53 N., R. 82 W. Section extends from creek level near the Flying E ranch to the old mine shaft 1 mile southeast.

?/. NW. i sec. 26, T. 53 N., R. 82 W. Section extends from the "upper slag" to the monument on Monument Peak.

2. Sec. 23, T. 53 N., R. 82 W. Section extendi from creek level near Collin ranch to the mine on the "upper coal," thence south to Monument Peak.

aa. SW. sec. 14, T. 53 N., R. 82 W. Section extends from mine above Collin ranch to the "upper slag" farther south.

66. NE. i sec. 14, T. 53 N., R. 82 W. Section starts at creek level.

cc. SE. i sec. 12, T. 53 N., R. 82 W. Section starts at creek level.

dd. NE. i NE. i sec. 24, T. 53 N., R. 81 W. Section starts from bench mark 4153.

ee. NW. i NW. i sec. 13, T. 53 N., R. 81 W. Section starts from level of Piney Creek.

//. SE. i sec. 10, T. 53 N., R. 81 W. Section starts from level of Pinev Creek.

gg, SE. i sec. 5 and NE. i sec. 8, T. 53 N., R. 81 W. The highest slag is that of the "upper coal."

hh. SE. 1 sec. 4, T. 53 N., R. 79 W. Section from bed of coulee to supposed Healy coal.

a. T. 53 N., R. 79 W. A general 82ction for the northwestern portion of the township, compiled from a profile section from Clcarmont to the "double crossing" of Clear Creek.

U. S. Oeolooical Survev

VUffAlJb COAL FIELD, WYOMIKG. 155

The record of the deep well at Clearmont, about 4 miles north of the township line, showing a section doubtless equivalent to that underlying most of this area, is as follows:

Record of deep well at Clearmont.

Feet.

Sandstone and shale 195

Coal 12

Sandstone and shale 101

Coal 18

No evidence of tlie quality or value of the beds thus reported has been obtained.

T. 53 A'., R, 80 ir. — The lowest coal bed exposed in this township is represented in the western part, where a rather pronounced group of coal beds outcrops on Clear Creek, approximately at water level, but the group is so broken by shale and bony partings that it rarely contains 30 inches of solid coal, so far as it has been observed within this particular township. This bed is doubtfully correlated with the Dry Creek bed to the south.

The Healy coal, which is the principal workable bed, is approximately 15 feet thick and occurs at an elevation of about 4,400 feet above sea level. It Jias been removed by erosion from the greater part of the township, but some areas remain, especially in the southwestern part, and to a smaller extent in the northwest corner. In many places, especially where the coal has been left in small areas on hilltops, it has burned, forming a conspicuous slag. A still higher bed, the Walters coal, about 170 feet above the 15-foot bed, remains in a few places. It is about 35 feet thick where exposed at its full thickness, but contains a great number of shale partings which render it of doubtful value.

Several other coal beds also are exposed, but though they are of good quality none of them are known to be above 2 feet 6 inches in thickness.

T, 53 N., R, 81 W, — The coal occurring near water level along Piney and Clear creeks, at the eastern edge of this township, clearly contains workable benches at some points. At this horizon 3 feet 9 inches of coal was measured at the mouth of Boxelder Creek, near the Hogerson ranch in sec. 14 (No. 7). Approximately the same bed, 6 feet or more in thickness, has been mined in the bank of Piney Creek opposite the old Sam Dickey ranch in sec. 8 (No. 5). It may be noted that this horizon is described as of no value in the report on the township to the east. A coal from 5 to 15 feet thick which probably represents the Healy bed is recognized at a horizon from 130 to 150 feet above this lowest coal, and another bed occurs from 150 to 170 feet above the Healy. (dd, ee,ff, gg.)

156 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1608, PaM tt.

The upper coal beds occurring above water level are largely burned along their outcrops. The uppermost bed is burned more extensively than those below and for this reason probably the greater part of the area noted as occupied by slag from this bed may be entirely devoid of this coal. In many places the underground extent of the burning is a matter of much uncertainty.

T, 53 N,j /?. 82 W, — Two principal beds are here recognized — the Healy and the Walters. Other coals near water level have been noted along the valley of Piney Creek and doubtless belong to the same group as that described at approximately the same elevation in the township to the east. Nothing is known concerning the coal beds that may be present below water level. The Healy bed is approximately 120 to 150 feet above water level and the Walters coal 150 to 170 feet above the Healy. The Walters coal is extensively burned on its outcrops along the summits of the higher ridges and may be completely burned out over a large part of the area occupied by the slag of this bed. In a small area in the southern portion of the township coal beds at still higher horizons remain and have been prospected to a slight extent, {w, x, y, z, aa, bbj cc.)

T. 53 N.y R. 83 W. — No complete sections of the coal-bearing rocks were obtained in this township. But one bed of coal was noted which may be over 30 inches thick. Unfortunately, no good exposures of this bed were found in which the coal could be measured or sampled. It is represented in the northeastern part of the township by an extensive bed of heavy slag, which was traced as shown on the map. It is thought to be the bed elsewhere described as the Healy coal of the Ulm coal group. A natural bank in the NE. sec. 2 revealed coal and brown carbonaceous shale to a thickness of 15 feet or more without exposing any bench tliat appeared of workable quality. This is, however, but negative evidence, for the great amount of burning at or near this horizon may be interpreted as indicating the possible existence of some more valuable portion of the bed. The western limit of this and other possible coal beds is concealed by the overwash of gravel. Coal is reported by several inhabitants at Kearney to have been mined for local use from a pit in the bed of Piney Creek, about one-fourth mile below the bridge that crosses that creek near the post-office. This locality, which would be about in the NW. J SE. sec. 26, was searched, and, although considerable coal of a woody, subbituminous quality was found scattered about in and near the creek, the coal bed was not seen in place and was probably covered by stream wash. An old map of Fort Phil Kearney published in Carrington's description of this territory in the pioneer days of early settlement" shows a bed of coal

aCarrlngton. H. B., Absaraka, land of massacre, 1878, p. 147.

Buffalo Coal Field, Wyoming. 157

in the bank of Little Piney Creek, evidently somewhat west of the present road crossing. This coal was not found in the present work. A well at Chris Hepps's ranch, a little over one-fourth mile south of the above-mentioned locality, is also reported locally to have been drilled to a depth of 200 feet, encountering much coal through a thickness of 100 feet. These beds are thought to represent approximately the horizon of the Healy coal.

Much slag was noted in the wSE. J sec. 36 and extending beyond the limits of this township, continuous with the one or more coals that are extensively burned about Lake De Smet. It can not be stated from the evidence at hand whether coal is or is not present at the horizon of the upper burned bed, but if valuable coal exists near stream level in Piney Creek near by, that lower bed, unbumed, doubtless underlies much of the adjoining area.

Little can be said as to the possible existence of other coal beds which may exist at considerable depth and whose outcrops are buried under the terrace and alluvial cover. Valuable coals of a considerably lower horizon than those exposed here are described by TafF as existing in the Sheridan field, composing the intermediate and Tongue River coal groups. He also notes, however, that as that part of the Fort Union including these lower coal groups is traced southward the coal beds thin out and disappear as the outer fringe of the conglomerate strata is approached, presumably owing to the more abrupt changes in sedimentation at places where the coarser deposits were accumulating in strong currents of water. It seems likely that the Kingsbury conglomerate member is a broad alluvial or delta deposit which locally represents the coal-bearing strata of adjoining fields and the extent of which, beyond the base of the mountain mass, is very uncertain.

T. 52 N,y R. 79 W, — As in the township to the west, three principal coal beds are here represented. The highest occurs at an elevation of 4,650 feet above sea level. It has been almost entirely removed by erosion. One exposure was found in the eastern part of sec. 18, where the coal measured about 9 feet (u). If this is to be correlated with the Walters coal in the township to the west, the bed evidently thins toward the east.

The only important beds in the township are the two at altitudes of 4,530 and 4,470 feet, which are taken to represent the general horizon of the Healy coal. Exposures of the two beds one above the other were found in the NE. J sec. 21. They are both of workable thickness and quality. A good exposure of the lower bed occurs in the NW. J sec. 3 (No. 16) and another near the south line of sec. 30. The two beds occur also near the east line of sec. 1. Their thickness varies but is everywhere more than 3 feet. They do not, however, form marked areas of slag in this township, although they ac vsx.

158 Contributions To Economic Geology, 1908, Part Ii.

many places burned to a slight extent. Owing to the character of the surface and the absence of burning it was impossible to trace a continuous outcrop of the coal, and for purposes of classification dependence must be placed on the contours with some allowance for possible errors in vertical control.

Numerous other beds of coal occur in this township, especially in the lower part of the stratigraphic section. It is thought, however, that none of them are constantly over 30 inches in thickness. They are too thin, too poor in quality, or too variant to be considered valuable.

According to R. W. Stone, as already stated, a 5-foot bed of coal outcrops at the level of Crazy Woman Creek, about the middle of the township east of this. It sliould be stated, however, that this bed seems to thin toward the west. Along Wildhorse Creek, 18 miles farther east, it varies from 8 to 30 feet in thickness, and along Clear Creek it seems to be represented by a bed which is not over 2 feet thick. wStill lower valuable beds outcrop on Powder River above and below Arvada, 9 miles northeast of this township.

In the deep well at Clearmont, 9 miles north of this township a 12-foot bed of coal is reported at 195 feet and an 18-foot bed at 308 feet; these beds may extend continuously underneath this area.

T. 52 iV., R, 80 W, — There are three beds of coal that deserve attention in this township. The highest, which is here termed the Walters coal, occurs at an altitude of 4,650 feet and where not removed by erosion has been for the most part burned. It is from 25 to 30 feet thick, but contains many bony seams and appears to vaiy much in quality from place to place.

At 120 feet below the bed just described occurs another, which, as measured m sec. 35, has a thickness of 13 feet (r). It is of good quality. Several exposures of this bed were found in the southeastern part of the township on the nortlieast flank of the divide, but in the northwestern part of the township no measurements were obtained, although several sections indicate coal or slag at this horizon.

Sixty feet below this bed, at an elevation of 4,470 feet above sea level, occurs another coal bed of about the same thickness. The two beds were found, one above the other, in sec. 3 of the township just south of this. They are taken to represent the general horizon of the Healy coal. In sec. 11 of this township a coal bed 13 feet thick appears to correspond to the lower of the two beds (No. 14). Heavy slag commonly occurs along the outcrop of these coal beds in the township. As the two beds are but 60 feet apart and are similar to each other, it is very difficult to distinguish between them in isolated exposures.

In the NW. sec. 32 of the township to the south, 1 1 feet S inches of coal is exposed in the bed of Dry Creek. If this bed is constant it

Buffalo Coal Field, Wyoming. 159

should underlie the greater part of this township, but its equivalent was not found here.

T. 52 N,, R. 81 W. — The lowest coal recognized in this township is approximately at water level. It was noted in sec. 35 and also in sec. 1. As it appears to differ in thickness and quality in different places and is usually much broken by shale and bony partings, it is doubtful if it can be considered generally workable, (n, o, p, q.)

In the NW. sec. 35 a coal bed 5 feet 10 inches thick was discovered 70 feet above water level (m). It seems probable, however, that this coal is not above 30 inches thick over an extensive area.

Probably the most important bed in this part of the field is that designated the Healy coal. This is noted at altitudes of 4,450 to 4,475 feet in the southern half of the township, west of Clear Creek. The altitude of a bed thought to be the same in the northwestern part of the area is slightly above 4,500 feet. A number of sections of this bed show the thickness to be from 13 to 19 feet, including $hale partings, which are, however, of minor importance. This bed has been mined for local use in the SW. SW. sec. 36, and a detailed section of the bed is given in Plate X, No. 13. It seems fair to assume that this is a workable coal bed throughout the township wherever it exists. Its outcrop is commonly indicated by a marked slag.

The so-called Walters coal, 170 feet above the Healy bed, is extensively burned in the higher ridges in this township, but where it remains unbumed it is of considerable thickness. It measured 28 feet of coal, including partings in the NE. NW. J sec. 3; 34 feet in the NW. NE. sec. 16; and 28 feet 4 inches in the NW. SE. sec. 18. The character of this coal bed is simihir in nearly all the exposures. In eath place some of the coal is evidently good. The weathering of the bed, however, brings out numerous thin bone and shale partings that break up the coal into minor benches, making the bed difficult to mine. If mined the coal would probably be high in ash. It is doubtful if the bed in many places is at present commercially valuable.

T. 62 iV., R, 82 W, — The principal coal bed within this township is somewhat doubtfully correlated with the Healy coal. The slag of three higher beds is present, but the coal is for the most part completely burned. No good exposures of the higher coal beds occur, although in the hill on the south side of sec. 4 an old entry on one of these beds was observed.

One of the pnncipal coal openings in this township is on the Healy bed in the SE. SE. sec. 3. The coal is exposed in the bed of a draw. The bed as shown in section No. 9, Phite X, contains about 9 feet of coal, excluding the shale partings, (See also t.)

160 Contributions To Economic Geology, 1908, Part Ii.

In the SW. sec. 12 is exposed a coal bed which is supposed to be the same as that in sec. 3, just described. The total thickness of the bed is 18 feet 7 inches, but the coal is too badly weathered to permit a detailed section.

In sees. 19 and 20, on the southwest side of Lake De Smet, two workable beds come to the surface at a horizon that seems to correspond to the Healy. The beds dip 4° NE. The interval between them was not measured but is approximately 60 feet. The upper bed is 6 feet, the lower 5 feet in thickness (No. 10). The coal in both is of good quality and has been mined to a small extent.

In the SE. sec. 1 of the township to the west at least 4 feet of coal is exposed in the bank of Shell Creek. This coal has probably been removed by erosion from portions of the alluvial flat north of Lake De Smet. No other exposures of the bed occur.

No coal beds were discovered southwest of those just mentioned near Lake De Smet. The coal beds near Arvada described by Stone and those of the Sheridan district described by Taff, were they continuous, should underlie this area and come to the surface between it and the mountains. No trace of those coal beds was found, however. The surface is partly obscured by the mantle of gravel that skirts the mountains, yet outcrops of bed rock may be found along the stream beds. It seems probable that the lower coal beds do not exist here and that they may be represented and replaced by the Kingsbury conglomerate member. (See also Jiy i, ;.)

T. 52 .v., R, S3 ir. — No coal bed is known in this township, the southwest half of which is occupied by rocks older than the Fort Union. The strata dip to the northeast.

Slag in the northeast corner of the township (in and near sec. 1) indicates a coal bed that appears to be for the most part burned. This bed is very doubtfully correlated with the Walters coal to the east. If this correlation is correct, there should be workable coal 170 feet below this bed. Little weight should be attached to such an assumption, as the information is too meager to warrant much more than a guess. The outcrop of the workable coal at the southwest end of Lake De Smet would probably be exposed through a part of this area were it n(>t concealed by the extensive gravel and bowKler beds, but that coal bed is known to vary in quality and thickness and can not be assumed to be continuously workable.

Coal was observed in the stream wash on the upper waters of Rock Creek, in the northwest corner of sec. 24. This is of a quality similar to that of the workable coals ()f this district, but no evidence of its source was found. It is assumed to be from some (>f the carbonaceous beds of the Piney formation, which are of no value in this general i*egion.

Buffalo Coal Field, Wyoming. 161

r. 61 N., R. 80 W. — The Dry Creek coal bed is exposed along the stream of that name in sees. 22, 29, and 32 (Nos. 23, 24, g). In sec. 32, 11 feet 8 inches of good coal was measured. No outcrops of this bed were found in the northeastern portion of the township.

The coal elsewhere referred to as the Healy bed occurs about 150 feet above the Dry Creek bed. It measures 16 feet in the NW. sec. 16, the coal being of good quality. It underlies an area of about 6 square miles in the northern part of the township and about 2 square miles in the southern part.

A thick bed of carbonaceous shale, including some coal, represents the Walters coal in this area and is found from 150 to 170 feet above the Healy.

T. 61. N., R. 81 W. — There are two principal coal beds in this township. The lower, which is here termed the Healy, occurs at an elevation of 4,500 feet above sea level. The Walters coal is 175 feet above the Healy bed.

A good exposure of the Healy coal occurs in the NW. SE. sec. 14 (d). Coal is obtained here for the Healy ranch on Clear Creek. The portion of the bed exposed is 10 feet thick and the coal is of excellent quality (No. 21). An exposure of the same bed occurs in the SW. SW. sec. 36 of the township to the north, where 17 feet 6 inches of coal is exposed (No. 13). A bed taken to be the Healy outcrops in the southern part of sec. 5 and in the NE. sec. 7. Just west of the township line, between sec. 18, T 51 N., R. 81 W., and sec. 13, T. 51 N., R. 82 W., are several abandoned entries which appear to be at the same horizon. A little east of the center of sec. 25 coal appears in the bed of a draw. It is of excellent quality and has been mined to a moderate extent. It appears to be at the Healy horizon (c). Coal of rather poor quality has been mined from a bed exposed in a draw in the western part of sec. 36. The interval to the next slag above is 150 feet. This coal is probably somewhat above the Healy horizon.

The Walters coal appears in small isolated areas along the divide between Clear and Dry creeks. In the southern part of sec. 13 the bed was formerly worked as an open bank. It measures 34 feet in thickness, but is so broken by partings of bone that it is inferior in quality to the Healy coal.

In the SW. sec. 20 a coal bed 12 feet thick is exposed which seems to be about 50 feet below the Healy (No. 22). In sec. 9 a bed of coal 3 feet thick appears at about this horizon, but no other exposures of the bed were f oxmd. It seems not unUkely that it varies in thickness and quality.

It is reported that in drilling a well at the Healy ranch a coal bed 30 feet thick was struck at 160 feet below the flood plain of Clear Creek. A few miles down Clear Creek, in the next township noTtk,

7963'— Ball. 381—10 11

162 Contbibutions To Economic Geology, 1908, Pabt Ii.

a coal bed at this horizon comes to the surface, but is much broken by shale and is of little value. (See also €,/.) .

T. 61 N., R. 82 W. — The slag that occurs along the east township line probably represents the Healy and Walters coals, the latter being 175 feet above the former. In many places the slag beds are so badly confused by slumping that it is difficult to distinguish the different horizons. Just east of sec. 13 several entries have been opened on a bed of coal, which is taken to be the Healy. In the SE. sec. 23 an entry has been opened at about the same horizon. This coal is said to have been rather poor in quality. In the SE. sec. 14 a series of beds at the same horizon is exposed in a coul6e (No. 17, 6). One of the beds is burning to a slight extent.

The Mitchell mine, in the NE. sec. 26, was opened in 1907. A section of the coal beds exposed in the slope is given in No. 18, Plate X. The bed at the top of the section was first worked. It contained good coal, but is so broken by shale partings that an attempt was made to reach other beds. A series of coals was encoimtered, of which the lowest bed is the one at present mined. Another bed over 4 feet thick occurs 10 feet above it. The coal beds dip slightly in a direction S. 40 W. When visited the mine was putting out about 50 tons a month. The slope is 220 feet in length and has an inclination of 33° from the horizontal. It is necessary to pump 3,000 gallons of water from the mine every twenty-four hours.

In the western part of sec. 36 is the oldest mine in this township, owned by G. W. Munkre. The coal bed here mined is 85 feet below the surface. Above it are numerous beds of bony coal, said to be of no value. The coal dips slightly toward the southwest. A section is given on Plate X (No. 19). The output of the mine during the winter months is about 27 tons a day.

It is reported that on the hill just southeast of Buffalo a drill hole was put down to the depth of 185 feet and that 52 feet of coal was encountered in the last 64 feet, but none of the beds was over 2 J feet in thickness.

In the western portion of the township outcrops are obscured by extensive gravel beds, and no coal is known.

T. 51 N.y R, 83 W, — So far as known no coal of value occurs within this township. In the northeast corner, however, some beds of coal and brown carbonaceous shale were found overlying the Kingsbury conglomerate member. The largest of these is in the bank of Rock Creek, near the township corner. Here one bed of coal measures about 6 feet in thickness, but is so poor in quality that it is probably of no value. Other carbonaceous beds doubtless occur in the older Cretaceous rocks of the area; but, as elsewhere stated, they are, so far as known, of no commercial value.

Buffalo Coal Field, Wyoming. 163

The rocks that outcrop in this township consist of the lower part of the Fort Union (' *De Smet and older formations. As these have a general northeasterly dip, they pass heneath and normally underlie the more valuable coal beds of this region, which occur at a horizon well up in the Fort Union formation, their base being estimated to lie from 1,500 to 2,000 feet above the Kingsbury conglomerate member. Several of the lower beds of this group are represented at the mines near Lake De Smet, about 2 miles northeast of this township, as already described.

T. 60 N.y R. 80 W. — A thick bed of coal has been observed outcropping at many localities near water level on Crazy Woman Creek in this township. It is thought to represent the bed elsewhere described as the Dry Creek coal, which is well exposed near the Healy sheep pens, on Dry Creek, a short distance north of this township. The measured sections of this bed near the southeast comer of the township are shown graphically in Plate X (No. 27). As this bed appears to be workable both northwest and southeast of this township, ranging from 6 to 12 feet in thickness, and as it also .outcrops in sec. 8, T. 49 N., R. 80 W., with a thickness of 6 feet, it seems fair to assume that it underlies the whole area and is also workable there.

The coal elsewhere referred to as the Healy bed occurs about 150 feet above the Dry Creek bed. Just west of the township line, in sec. 24, T. 60 N., R. 81 W., this coal is exposed in the creek bank. It is 11 feet thick and the quaUty is good (No.V26). The same bed outcrops in the NE. sec. 7, the NW. sec. 8, the SE. sec. 3, and the NE. J sec. 10. Exact measurements were not obtained, but the bed appears to be of fairly imiform thickness. It underlies a considerable area along the divide between Dry and Crazy Woman creeks, as shown on the map.

From 150 to 170 feet above the Healy bed is found the Walters coal, which is here a thick bed composed largely of carbonaceous shale with coaly streaks and is of doubtful commercial value. Slag on one or two of the highest summits near the center of the township represents coal beds higher than the Walters coal. These are, however, completely burned out.

T. 60 iV., R. 81 F.— Above the road in the NW. i sec. 5 of this township several entries have been made on a coal bed just below the slag that caps the ridge. The old workings are now abandoned and no exposure of the coal was seen. On the flat in the SW. sec. 5, a slope has been sunk to a bed some 25 feet below the surface. This coal is reported to be of excellent quality and to have a thickness of about 10 feet (No. 25).

In the NE. sec. 24 a coal bed that is taken to represent the Healy occurs at creek level (a). It is 1 1 feet in thickness and of excellent quality (No. 26). In the NW. sec. 12 an exposure of a bed of boivY

164 Contributions To Economic Geology, 1908, Pabt U.

coal occurs at almost the same horizon. These beds may be identical, but it is the opinion of the authors that one occurs a little above the other, the two being so near together that it is impossible to distinguish them in isolated exposures. A good coal appears at this horizon in sec. 25 of the township north of this.

The coal beds above the Healy coal in this area may be disregarded so far as present availability is concerned. They occupy only a small area and are for the most part burned.

About a mile northeast of this township a 10-foot bed of good coal outcrops at water level in Dry Creek. On Clear Creek a bed at the same horizon is so broken by shale partings as to be of little value, but to the south along Crazy Woman Creek this bed runs from 6 to 8 feet in thickness as far as Trabing. It seems probable that this coal underlies the township under discussion, but, as stated, it may vary in quality and section.

r. SO iV., R. 82 F.— The southwestern half of this township is occupied by rocks older than the Fort Union. Of the Fort Union itself chiefly the lower portion, which is apparently barren of workable coal beds, is exposed within the area. The strata dip to the northeast at very slight angles. The upper Fort Union coal beds occur just north and east of the township. The Munkre mine in sec. 36, T. 51 N., R. 82 W., is about half a mile due north of sec. 1 in this township. An exposure of coal over 3 feet thick outcrops less than one-fourth mile east of the southeast comer of sec. 1. A well on the Jones ranch in the center of sec. 7, T. 50 N., R. 81 W., half a mile east of sec. 12 of this township, is reported to have shown the following strata:

Section of coal beds in well in sec. 7, T. 50 N., R. 81 W.

Feet.

Clay and gravel 20

Coal 32

Clay 5

Coal 8

Clay 4

Coal 8

Clay 1

Coal : 32

Interval drilled below this, but showing no coal 50

In interpreting this well record, however, it must be remembered that the thick beds of coal noted therein may not have been of workable quality and that a carbonaceous shale might easily have been interpreted as coal by a driller not experienced in the identification of workable coal. From the evidence in the adjoining townships it would seem fair to assume that at least a portion of the valley area

Buffalo Coal Field, Wyoming. 165

in the northeast comer of the township may be underlain by beds of workable value.

T. Jfi N.f R. 80 W. — The township is underlain by the upper beds of Fort Union age, 'including the coal beds of the Ulm coal group as distinguished by Taff in the Sheridan district. The strata show a low dip to the southeast through the northern part of the township, although the principal workable coal bed remains approximately at water level along Crazy Woman Creek across the whole township. Some slight structural irregularity was noted east and northeast of the Bilderbach Lakes, this being apparently a low anticlinal warp separating them from the valley of Crazy Woman Creek.

A large part of the western half of the township is composed of low, broad, flat valleys and slopes covered by a white clay soil strewn with scattered pebbles and bowlders, but showing no bed-rock exposures. Beyond these lower valley lands are terrace or mesa remnants capped by heavy deposits of gravel and bowlders. Over most of this area no evidence whatever of the underlying bed rock or the coals that it may contain was to be had from a mere examination of the surface.

The Dry Creek coal is exposed at various points along Crazy Woman Creek throughout the township, as already mentioned. In the northem portion of sec. 23, 10 feet of coal was measured. The bed is of considerable thickness also on the north side of sec. 1. In the NW. sec. 8 is exposed 6 feet of good coal which is thought to represent the same bed. The slight doming of the strata in the central part of the township makes the distribution of this coal bed uncertain. Over portions of the area it has been removed by erosion and the rolling grassy surface makes the outcrop difficult or impossible to trace.

A bed of good coal that occupies small areas in the central and southeastern portions of the township is about 130 feet above the bed of Dry Creek. It is thought to represent one of the coal beds at the Healy horizon. In the SE. J sec. 22, feet of good coal is exposed in this bed. In the SE. sec. 15, 5 feet of coal is exposed, but in the SW. sec. 11 this bed appears to be worthless. Because of the doming of the strata the area underlain by this coal in the central part of the township is probably not over 2 square miles. In the southeastern portion of the township the same bed was noted in the SW. i sec. 35, where 5 feet of good coal is exposed.

T. 49 N., R. 81 W. — The greater part of this township is occupied by the gravel terraces that skirt the mountains. The rocks belong to the lower portion of the Fort Union formation. They dip northeastward at very low angles. So far as known only one exposure of coal occurs within the township, and this bed is but 2 feet in thickness. It occurs in the NE. sec. 35. In sec. 2 an exposure of slag occurs, but the coal by which it was formed was evidently much

166 Contributions To Economic Geology, 1908, Part 11.

broken by shale partings. The valuable coal beds lie to the northeast outside the limits of the township.

T. 48 N.J R. 80 W. — As in adjoining townships, the geologic structure and stratigraphy of this area are very simple. The underlying strata are of Fort Union age, including the Ulm coal group as distinguished by Taff in the Sheridan* district. They lie nearly horizontal, showing at places a low dip to the east, but in the absence of accurate level data the dip can not be positively detennined. The northwestern part of the township is largely covered by surficial beds of bowlders and gravel that form an upland terrace or area of rolling topography and conceal most of the bed rock. The broad bottom lands of Crazy Woman Creek are largely concealed in a similar maimer by the more recent alluvial deposits. The outcrops of coal from 6 to 8 feet thick that were discovered at various places along the creek valley apparently represent an approximately continuous horizon, which is taken to be that of the Dry Creek coal bed, but its extent beyond the limits of the actual outcrops is very uncertain. East of Crazy Woman Creek the bed-rock formations are more continuously exposed but show very little evidence of coal either in outcrops or by burning. Coal reported on the Powder River side of the divide, east of this township, may correspond to the coal found in Crazy Woman Creek. This appears to give some warrant for supposing the whole area east of the creek to be underlain by workable coal.

The Dry Creek coal mentioned above is mined in the bank of the creek in the SE. sec. 30, where about 10 feet of good coal is exposed. In the SW. sec. 21 this coal appears in two benches of 7 feet and 4 feet (No. 30). In the NW. sec. 15, 10 feet of coal is exposed (No. 29), and in the SE. sec. 3, 5 feet on the same bed (No. 28). Other exposures occur along the creek at intervals throughout the township-

T, 48 N.J IL 81 W. — The greater portion of this township is covered by the Fort lnion formation. The beds rise gradually from northeast to southwest across the township, and in sees. 30 and 31 the underlying shale of the Piney formation comes to the surface with a dip of 10° and a strike of N. 17° W. For the most part the country is gently rolling and grass covered. Along Crazy Woman Creek marked gravel terraces are developed. No coal is exposed within this township]).

In the SE. sec. 30 of the township to the east 10 feet of good coal outcro])s in the bank of Crazy Woman Creek, as already described, and this bed may be traced downstream throughout the township, its dip being about equivalent to the grade of the creek. This coal bed may or may not underlie the eastern part of the township under discussion. No trace of it was found, as there are very few bed-rock exposures of any kind in this area.

Buffalo Coal Field, Wyoming. 167

In sec. 17 of the township to the south two coal beds 8 feet thick come to the surface with a dip of 7® and a strike of N. 18® W. These beds appear to vary in thickness along the outcrop. No exposures of them were found north of Crazy Woman Creek, and it seems doubtful whether or not they are present in this township.

T. 47 N., R. 80 W, — Very few exposures of any sort occur within this township. The country is for the most part gently rolling and grass covered. The rocks are probably of Fort Union age. To judge by dip readings north and west.of the area, there appears to be a slight dip to the southeast in the northwestern part of the township. For the most part, however, the rocks seem to be horizontal.

In the SE. sec. 30 of the township to the north 10 feet of coal has been worked in the bank of Crazy Woman Creek. This bed can be traced downstream throughout the township. If it is continuous southward it underUes the township under discussion, but no definite statements can be made concerning it.

In the western portion of the township to the west several coal beds from 3 to 8 feet thick come to the surface with a dip of about 7® and a strike of N. 18® W. These beds do not, however, appear to be constant in thickness along the outcrop. It is not unlikely that they vary in quality and thickness from place to place and that they underlie this township at too great depth for profitable mining.

T. 47 N., R. 81 W. — The eastern half of this township is covered by the rocks of the Fort Union formation. These rise gradually toward the west, and in the middle of the township the basal beds come to the surface with a dip of 9® and a strike of N. 18® W. Farther west the shale of the Piney formation appears below the Fort Union.

There are two groups of workable coal beds in this township, one at the base of the Fort Union and one at the top of the Piney. The best exposure of the Fort Union coals occurs in the eastern part of sec. 28 in a deep coul6e (No. 36). At the base of the section exposed is a bed of good coal about 6 feet thick. Above this are a number of unimportant beds of coal and coaly shale. The bed may be traced for three-fourths of a mile northeastward, but beyond this point it is covered. No exposure of a bed comparable in thickness to this one is to be found to the southeast, and it is impossible to say how regular this coal may be in thickness and quality.

Considerably above this horizon, about three-fourths of a mile to the east, a bimk has been opened in the NE. J sec. 27, where 4 feet of good coal is exposed. This bed seems to be about on the strike of the line of slag hills in sees. 10 and 15 and may represent the same bed. No other exposures of the coal bed are to be found, however.

Two workable beds of coal near the top of the Piney formation are exposed in sec. 17. The upper bed contains 7 feet 6 inchfta ol

168 Contributions To Economic Geology, 1908, Part H.

solid coal. An entry 60 feet in length has been run in on this bed, in the SE. i SW. i sec. 17, to supply coal for local use (No. 33). Ten feet above this bed is another one 3 feet 4 inches thick.

Some 30 or 40 feet lower in the section is a bed containing 8 feet of coal (No. 32). Although somewhat broken by shale partings, this bed is still workable.

In the NE. J sec. 29 and the NW. i sec. 28 (No. 35) coal beds 30 inches or more in thickness were found, but they are in no way comparable to the beds above described. If they represent those coals, the beds have decreased greatly in value. In the northwestern portion of the township, along the line of strike of these coals, exposures are obscured by the alluvium of Crazy Woman Creek or by gravel.

T. 43 N,, R. 79 W. — This township is situated on Powder River, 18 miles south of the area shown on Plate X. It was examined at the close of the field season, after the disbanding of the party, in anticipation of future work. It gives a general idea of the geology of a considerable belt of coal-bearing rocks which come to the surface along the fiank of the Salt Creek dome in this region. As the township is outside of the area of the large map, a separate diagram from the original field sheet is here reproduced (PL XI).

The general succession of the rocks has been described under Stratigraphy. '' On the north side of the river most outcrops are obscured by extensive gravel-covered terraces. Here the rocks appear to be for the most part horizontal, but in the NE. i sec. 8 a dip of 1° NE. was observed, with a strike of N. 75° W. South of the river the beds rise gradually, with increasing dips, until they form a marked ridge extending across the southern portion of the township, in which the beds dip from 15° to 18°. Behind this first ridge is a valley and south of that still another ridge, the rocks dipping The strike in the southwestern portion of the township is N. 81° W. In following the ridge westward the strike swings somewhat toward the north.

In the SW. i sec. 30 a dip of 22° was observed. It is estimated that from that point northeastward about 5,100 feet of strata are exposed. No dips were measured southwest of this point, but the beds gradually flatten in that direction. The coals are confined to a narrow belt just north of the marked sandstone ridge. Detailed stratigrapliic sections of the barren strata were not made.

Coal occurs at only one horizon in this townsliip, flanking the high pine ridge on the northeast. There are two principal coal beds 90 feet apart (Nos.37, 38, PI. X, 1, 2; PI. XI). In the northern portion of sec. 36 both are good, and coal is obtained for local use from the upper bed. In sec. 26, only three-fourtlis of a mile northwest of the open mine, the upper bed is bony and of no value, but the lower bed

Coal min*

Coal protfMct or expourc

Strike and dip of rock*

-f

comer found

Buffalo Coal Field, Wyoming. 169

appears to be good and was formerly worked in the SW. sec. 26 for a short time (PL XI, 2). H. W. Davis states, however, that the coal ran so high in sulphur that it could not be used as a domestic fuel. It is impossible to trace the coal beds beyond the middle of sec. 27, for they are concealed in the Salt Creek valley and on the rolling grassy divide beyond. Beds which appear to represent the same horizon are worked in T. 44 N., R. 81 W.

There seems to be no doubt that these coal beds vary in quality and thickness. It is calculated that the upper bed is approximately 1,200 to 1,300 feet below the surface at the Davis ranch. It probably underlies all the northeastern portion of the township at about that depth, as the rocks are nearly horizontal.

The Coal Field In The Southeastern Part Of

The Bighorn Basin, Wyoming.

By E. G. Woodruff.

Introduction.

This paper is a preliminary report on the coal field in the southeastern part of the Bighorn Basin, Wyoming,* extending from No Wood Creek, on the north, around the southciastern point of the basin to Bighorn River.

During the summer of 1907 C. W. Washbume examined the coal fields on the east side of the basin from a point north of the Montana line as far south as No Wood Creek, and during the same* time the writer examined the coal fields on the west side from the Montana line to Bighorn River. The field described in this report lies between the two just mentioned and the work in it completes the study of the coal beds of the Bighorn Basin. All of this work was done imder the immediate supervision of C. A. Fisher, who had previously made a reconnaissance survey to obtain data for a report on the geology and water resources of the region.

Max A. Pishel served as principal assistant in the field and rendered valuable services in the office in compiling data for the map. Jay H. Cather and Roy L. Nelson also assisted in the field work and much of the value of this report is due to their intelligent cooperation. The purpose of the work was to examine the coal beds and to determine their situation with respect to the points located by the land surveys of the area, in order that the public land containing coal might be segregated from noncoal land and a value placed on each legal subdivision containing a workable bed of coal. As a basis for this classification the coal beds and geologic formations were studied in the field and their position and extent were shown on a map made during the progress of the work. A copy of the map is included in this report as Plate XII. The relative positions of objects shown on this map were determined by horse pacing in the northern part of the field and by a system of triangulation by plane table in the southern part.

Marked land corners were found to be lacking except along No Wood Creek and Bighorn River, where resurveys have been made.

a A detailed report on the eoal of tlie Bighorn Basin is now in course of preparation, to be Issued later as a separate bulletin.

b Fisber, C. A., The geology and water resources of the Bighorn Basin, Wyoming: Prof. Paper U. S. Gol. Survey No. 53, 1906.

COAIi IN S0UTHEA8TEBK PABT OF BIGHOBN BA8IN, WYOMING. 171

As a result of this condition the outcrops of coal beds can not be accurately located with regard to land lines. It should be borne in mind, therefore, in consulting the map, that locations in the interior of the field are only relative and not determined with reference* to land comers.

Location And Extent Of The Field.

The coal-bearing rocks outcrop in a belt 6 to 12 miles wide, extending southeastward from the lower course of No Wood Creek along Sand and Cottonwood creeks to the east side of the ''Honeycombs," then turning west across No Water Creek to Bighorn River. The field contains about 600 square miles. It is limited on the west and northwest by badlands and on the east and southwest by the dissected plains adjacent to No Wood and Kirby creeks. The region partakes of the character of both provinces — badlands on one side and broken plains on the other. The extent of the field is shown on the map (PI. XII), and its location in a larger area by the smaller index map on the same plate.

Topography.

The accessibility of coal and the ease with which it is transported from any region depend on the topography ; hence a detailed description of the siurface features is given. Erosion is rapidly progressing everywhere, forming deep, narrow valleys, across which wagon roads are maintained with difficulty. In the northern part of the field Sand Creek follows the strike of the beds from the southern part of T. 47 N., R. 91 W., to No Wood Creek, in a narrow gorge joined by many small branches flowing in deeply cut channels from the moderately dissected regions on either side. One wagon road from Bonanza to Worland crosses this coul6e in the northwestern part of T. 48 N., R. 91 W., and another from Tensleep to Worland extends across the badlands near the head of the stream. On both of these roads the grades are so steep that heavy loads can be hauled over them only with great difficulty.

Cottonwood Creek, which drains the region east of Sand Creek, has a number of branches in the badlands in T. 46 N., Rs. 89 and 90 W., that join near the north line of the township to form the main channel. From the junction of these branches the creek flows northward in a broad, moderately open valley. The Worland-Tensleep road crosses this creek miles north of the junction of the main branches. Another wagon road from the north extends up the valley to the small coal mine in sec. 34, T. 47 N., R. 90 W., and thence over the divide to Little Cottonwood Creek. The road to Tensleep is very hilly, but the one in the valley crosses only a few hills and most of these are short.

The head branches of Little Cottonwood Creek have cut the ate north and northwest of Tensleep Butte into sharp iidgea xA

172 Contbibutions To Economic Geology, 1908, Part U.

points separated by narrow V-shaped valleys. Though no wagon road crosses this area, it would be possible to construct one from Bud Elmball Draw leading through the badlands west of Tensleep Butte and along a divide into the valley of Cottonwood Creek.

Bud Kimball Draw and Buffalo Creek rise on the edge of the badlands locally known as the ''Honeycombs" and extend eastward across the area. There is a narrow belt of badlands about the heads of these streams along that part of the west side of the field, but elsewhere the topography is that of a moderately dissected plain crossed by coul6es or narrow steep-sided gorges. This portion of field can be traversed with moderate ease along the streams or divides, but passage across them is difficult. The only wagon road leading to this district enters from the east and terminates in the district; the badlands on the west and coul6es difficult to cross in a northsouth direction prevent access over roads from other directions. One of the minor roads follows Bud Elmball Draw from the valley of No Wood Creek to the mine at the head of the draw and has a northeast branch to Tensleep; another leads along the divide between Buffalo Creek and Bud Kimball Draw to coal prospect No. 6, near North Butte.

The southeastern part of the field is traversed by No Water Creek and its branches. The name aptly describes the character of this stream, though at times the flood water from a large area finds its way to Bighorn River through its channel. The stream enters the field from the southeast in T. 44 N., R. 90 W., and continues in a northwest course for about 15 miles. The branches from the southwest are short and steep from their soiurce along an escarpment of northeastward-dipping beds; the branches from the northeast are longer and have a smaller gradient. A road with many short, steep grades follows the valley in general, but is forced away in many places by deep, narrow gorges cut by the branches where they enter the main channel. This road passes the No Water mine and fiu:- nishes a difficult outlet for the coal. Other roads enter the No Water Valley from the area across the divide to the east.

Kirby Creek drains the southwestern part of the field, and a few short, steep-sided ravines rise in the high rugged Winchester Hills and extend directly to tlie narrow valley of Bighorn River. Wagon roads extending down the Kirby Creek valley and coming into it from the north lead to fords at several places along the river.

The workable coal beds of tliis field are not easily accessible, because of the rough character of the country as described above. They lie in badlands or slightly dissected plains, and, with the exception of the beds near Bighorn River, are more than 10 miles from market. The region is uninhabited except along No Wood Creek and Bighorn River, and the only running water found throughout a great part of the area is derived from alkaline springs. One well in the valley of Buffalo Creek contains a small quantity of slightly alkaline water, And another in the vp" 'ttonwood Creek at the crossing of

COAIi IN SOUTHEASTEBN PART OF BI6H0BN BASIN WYOMING. 173

the Worland-Tensleep road furnishes about a barrel a day. No crosses the coal field, though a branch of the Chicago; Burlington and Quincy Railroad runs along Bighorn River, on the westem edge of the area mapped, to Kirby. In many places the wagon roads are poor and have uneven gradients.

Geology.

Stratigraphy.

The only geologic report on this field is that of C. A. Fisher,* who recognized that the coal-bearing rocks were susceptible of subdivision into several formations, but the time at his command and the nature of his work demanded the mapping of only broad divisions.

As recognized by the present writer, the order, age, character, and thickness of the formations are shown by the following table:

Coal-bearing and associated formations in the southeastern part of the Bighorn Basin,

System.

Group.

%

H

Formation.

Wasatch formation.

Fort Union formation.

Character.

Sandv shale and conglomerate, gray, pink, and yellow colors alternating.

Unconformity.

This formation occurs in two divisions; the upper member is vellowish tan, gray, and lavender colored sandy shale and sandstone; the lower member is yellowish tan and rusty colored, slightly sandy shale, with lenses of coal locally developed in the lower part.

Unconformity.

g

UndllTerentlated Montana.

These roclpi may be separated Into three divisions. The upper member consists of gray and yellowish tan sandy shales, alternating with brown carbonaceous shale and coal beds. These where recently eroded form a somber-colored banded exposure.

The middle member consists of very soft yellow sandstone and sandy shale and soft sandstone concretions. This member thins rapidly to the west.

The lowest member is made up of soft gray sandstone, slightly cross-bedded, containing occasional thin layers of mud-ball conglomerate and macerated carbonaceous material.

Claggett (T) formation.

Eagle (T) sandstone.

Yellowishtan massive thick-bedded sandstone and tan-colored sandy shale, and a few beds of gray and brown sandy carbonaceous shale.

Colorado shale.

Yellowish-gray massive thick-bedded sandstone and yeUowish-gray sandy shale Beds of carbonaceous shale and. coal occur here and there in the sandy shale member.

The upper part of this formation is tan-colored thin-bedded sandstone and sandy shale.

Thickness (feet).

Not wholly exposed in this field.

1,200

to

2,900

200 to 300

100 to 200

Not wholly exposed in this field.

The ceolocy and water resources of the Bighorn Basin, Wyoming: Prof. Paper U. S. Qeol. Survey No.

III nMUMlMii part of the area all these formations are more shaly than

174 Contributions To Economic Geox,Ogy, 1908, Pabt H.

The lines between the formations given in the above table are based on a consideration of both stratigraphic and paleontologic evidence. The beds have been examined by T. W. Stanton at several points between the type localities in Montana and the Bighorn Basin; and by C. A. Fisher at closer intervals in the same area, and have been traced from Bridger, Mont., in the Clark Fork valley, to Basin, on Bighorn River, by C. W. Washbume. Mainly on stratigraphic evidence these observers report beds which probably represent the Eagle and Claggett, and they find some indications pointing to the presence of the'Bearpaw and Judith River, though the evidence for exact correlation of these upper rocks with formations recognized elsewhere is insufficient. T. W. Stanton and F. H. Knowlton visited the field discussed in this report and have since examined the fossils collected during the progress of this work. They report that the fossils are not sufficiently distinctive to prove with certainty that the Eagle sandstone and Claggett formation are represented, and are still more doubtful concerning the correlation of the upper beds. Some species found elsewhere in the Judith River formation occur in the lowest members of the undifferentiated Montana, but they are not sufficiently distinctive to prove that these beds are of Judith River age. A consideration of the combined stratigraphic, lithologic, and paleontologic evidence, however, points to the presence of the divisions of the Montana group given in the table. The identification of the Fort Union is based on fossil plants, which have been identified by F. H. Knowlton as undoubted Fort Union forms. Some species of fossil plants found in these beds also occur in the " Laramie '' of neighboring regions, but no fossils clearly distinctive of that formation were found in the southeastern part of the Bighorn Basin.

The upper part of the Colorado shale is exposed on the eastern and southern borders of the area mapped on Plate XII. It is a mass of yellowish, slightly ferruginous, thin-bedded sandy shale and shaly sandstone, 200 to 300 feet thick. North of Kirby Creek it contains lenses of massive sandstone 20 to 30 feet tliick and several miles long. The middle part of the formation, which is exposed just outside of the area mapped but passes beneath it, consists of several hundred feet of dark-colored shale, which grades upward into the rocks of the upper part, just described.

The Eagle (0 consists generally of two yellowish-gray massive members, one at the top and the other at the bottom of the formation, and a thick bed of sandy shale between them, but locally three or four beds of sandstone and intervening shale are present.

Wliere it is exposed just east of Bighorn River, near Kirby, the formation is composed of a massive yellowish-tan sandstone 50 feet

COAIi IN SOUTHEASTERN PART OF BIGHORN BASIN, WYOMING. 175

thick at the bottom, overlain by 80 feet of gray sandy shale containing beds of carbonaceous matter and two coal beds of workable thicknesSf and at the top a massive yellowish-gray sandstone 60 to 75 feet thick. The formation contains similar members where it is exposed at the north end of the field near No Wood Creek, but toward the middle of the area the sandy beds lose their massive character and become more shaly, until the formation is changed entirely from its typical aspect, the carbonaceous shale becoming less abundant and. the coal beds disappearing.

The Claggett(?) formation lies conformably above the Eagle (?) sandstone, but differs from it in lithologic character. Near Bighorn River it consists of yellowish-tan massive beds, but to the east the sandstone gradually becomes shaly until the whole formation is composed of yellowish-tan shale beds with a few irregular sandstone members. Beds of brown carbonaceous shale and coal are numerous within the sandy shale, but none of the coal beds is thick enough to be mined.

The beds lying above the Claggett(?) formation and below the unconformity that separates the Montana group from the Fort Union are imdifferentiated in this area because of insufficient paleontologic evidence. The fossils show that the beds are of Montana age, but they are not distinctive of either the Judith River or the Bearpaw formation. On lithologic grounds the rocks are divided into a lower, a middle, and an upper member. The lower division consists of gray cross-bedded sandstone, containing thin, irregular layers of flat arid mud-ball conglomerate with macerated plant fragments and mineral charcoal. East of Bighorn River and about Tensleep Butte this member is eroded into prominent gray cliffs, and between Buffalo Creek and Bud Eamball Draw small areas of toadstool forms mark its line of outcrop. This member contains only small amounts of carbonaceous matter and no coal.

The middle division of the undifferentiated Montana is formed of beds of rusty-colored shale with here and there a layer of ferruginous sandstone. It diminishes in thickness from 90 feet at the north to less than 40 feet at the south. It is uniform in character from top to bottom, and contains no coal beds. No fossils were found except a few casts of small worm burrows.

The upper division of the undifferentiated Montana is composed of beds of ash-colored, tan, and drab sandy shale and brown carbonaceous shale with beds of coal. These beds range in thickness from a few inches to several feet. When freshly eroded the member is easily recognized by the somber-colored banded exposure. On account of an erosional imconformity above, the thickness varies greatly. Fossil leaves foimd in various locahties indicate that the

176 Contributions To Economic Geology, 1908, Part H.

beds are of fresh-water origin and possibly of Judith River age. Beds of coal are found in the member wherever it is exposed, and beds of workable thickness occur in the valley of No Water Creek on both sides of the channel. A section of one of these beds (No. 7 where it has been mined on No Water Creek shows 4 feet 11 inches of good coal, above which there is 7 inches of drab shale, then 6 inches of coal. Other beds almost thick enough to mine are exposed along Sandy Creek and between Buffalo Creek and Bud Kimball Draw, east of the "Honeycombs."

The Fort Union formation comprises two membera, which can be distinguished more or less clearly throughout the field. The lower one consists of yellowish sandy shale and rusty sandstone resting unconformably upon the undifferentiated Montana. These beds weather so uniformly to yellow that in the field they were termed "yellow beds.'' The member is about 775 feet thick where it is crossed by the Worland-Tensleep road, and 2,300 feet near Bighorn River east of Kirby. These two measurements represent about the average limit of variation. This part of the Fort Union contains coal at the head of Bud Kimball Draw, where a mine has been opened on a lenticular bed 5 feet 6 inches thick at its maximum (No. 4), and also at the head of Cottonwood Creek (No. 3), where a little mining has been done. Some coal has also been mined from a small outlier northwest of Cedar Ridge (No. 6).

The upper member of the Fort Union in the northern part of the field is composed of gray and grayish-drab sandy shales and many thin lenses of yellow sandstone. To the south, however, the sandstone members become more numerous, massive, and yellow, but are still darker than the yellow beds below. This member contains no coal beds. Where crossed by the Worland-Tensleep road it is 225 feet thick; east of Kirby it is 600 feet thick.

The Fort Union as a whole contains an abundance of leaves, from which its age has been determined. It is composed of beds rapidly deposited under climatic conditions unfavorable to the accumulation of vegetable matter and consequently contains little coal. The formation is separated from the Wasatch above by an unconformity which is not clearly displayed in most localities but is sufficiently well shown at a few points to establish the break with certainty.

The Wasatch formation consists of sandy shale, mostly tan-colored, with some yellow, brick-red, and maroon beds. The bright colors give a banded appearance to the freshly eroded surface and where the rocks are weathered impart a pinkish cast to the detritus. The formation is exposed along the western and northern margins of the field, and in the great badland area to the west in the central part of the Bighorn Basin. The Wasatch contains no coal in this field.

o Numbers in parentheses refer to locations on Plate XII.

COAIi IK 80UTHEA8TEBK PAST OF BIQHOBN BASIN, WYOMINQ. 177

Its age is fixed by vertebrate fossils found elsewhere in the Bighorn Basin by previous workers.

Structure.

The area here considered lies on the edge of a broad, moderately depressed structural basin. The beds have a general dip to the westnorthwest, north, or northeast, varying from 3° to 56°, modified in only a few localities by minor folds or faults. From north to south the minor structural features may be described as follows: Between the north line of the field and the Worland-Tensleep wagon road the beds dip between 3° and 32° a little south of west. To the southeast, about Tensleep Butte, the dip is less and the strike changes more to the south. Northeast of this butte a small fault cuts the lower beds. The direction of this and other faults in the field is shown on the map (PI. XII). Farther south, in the vicinity of the "Honeycombs,'' the rocks have a gentle dip, but to the east of that locality they are broken by a small fault. In the southern part of T. 45 N., R. 89 W., the beds are moderately folded, the strike turns sharply to the west, and the dip increases to 56° in sec. 35, T. 45 N., R. 90 W.*, but toward Bighorn River the dip again decreases to 10°. Near the river the beds are broken by several small faults. Wherever the coal beds are exposed in the area, however, the structure is not unfavorable to coal mining.

The Coal. Occurrence And Development.

This field contains coal beds of workable thickness in four separate districts — near the head of Cottonwood Creek, on Bud Kimball Draw, along No Water Creek, and north of Kirby Creek, near Bighorn River. Beds of considerable thickness, but too thin to mine, outcrop along Sand Creek, between Bud Kimball Draw and Buffalo Creek, along No Water Creek, and in the region between Kirby and No Water creeks. Beds of coal are widely distributed throughout the area, but their location is not given on the map, because they are too thin and of too small extent to be commercially valuable now. The outcrop of the beds of coal and sections measured at various places along the exposures are shown on the map (PI. XII).

It has been stated previously that one object of the survey was to determine the relation of the coal beds to land lines. This object could not be successfully accomplished because no reliable corner stones or posts were found, except along No Wood Creek and in the southwestern part of the area, near Bighorn River. The land lines could, therefore, not be established in the field, and the lines shown on the map are only suggestive and are not supposed to show the exact

178 Contributions To Economic Geology, 1908, Part H.

position the lines will occupy when they are resurveyed. Locations in the greater part of the area were found by a system of triangulation that established with a fair degree of accuracy the position of the coal beds in relation to hills, streams, and other landmarks.

Beds of coal thick enough to be mined occur in the Eagle ( t) sandstone, the upper member of the undifferentiated Montana, and the lower member of the Fort Union formation. In adjoining areas, notably in sec. 29, T. 48 N., R. 89 W., a coal bed occurs in rocks which are geologically older than any that outcrop in this area and to which Darton has given the name Cloverly formation.

It is generally supposed that the coal in the older geologic formations is of better quality than the coals deposited later. In this field only a few hundred feet of strata separate the lowest and highest beds and all have been influenced by the same structural movements. If there is a difference between the lower and higher coals due to geologic conditions it has not been detected by field study; however, the analyses given in the table (p. 183) seem to show that the coal in the lower beds is slightly better than that in the upper beds.

The mines of this field are small; in fact, none of them are more than prospects, though at several places a few tons of coal have been mined annually for a number of years. To begin at the north end of the field, the first coal bed which has been prospected is on Sand Creek, in the NW. i NE. i sec. 10, T. 49 N., R. 92 W., in the undifferentiated Montana. At this locality there is a prospect 100 feet deep on a bed which dips 18°. A section of the coal bed measured at a point 25 feet down the slope from the mouth is shown by section No. 1 on Plate XII. An examination along the entry and the outcrop of the bed shows that it is very lenticular and contains a large amount of shale and sandstone. The coal is subbituminous.

The next opening to the southeast has been made on a bed of coal in sec. 8, T. 48 N., R. 91 W., also in undifferentiated Montana rocks. The location of this prospect and a section of the bed at that point are shown on the map (No. 2). The dip of the beds here is 27° SW. The prospect in which the section was measured was driven about 75 feet and abandoned. It was found by following along the outcrop that this bed of coal disappears beneath surface cover a short distance to the north, but where last seen it is thinner than at the prospect. In the opposite direction from the opening there is only 14 inches of coal in an exposure one-fourth of a mile south, and in sec. 17 only a few inches of coal occur at this horizon.

Farther south along Sand Creek thin beds of coal outcrop at a number of points. The thickest bed in this group is exposed on the east side of Sand Creek, about 3 miles northwest of the Worland-

o Darton, N. 11., The geology of the Bighorn Mountains: Frof. Paper U. S. Oeol. Survey No. 51, 1906, p. 50.

COAIi nr SOUTHEASTERN PABT OF BIGHORN BASIN, WYOMING. 179

Tensleep wagon road. The coal at this place is in two benches, the thicker of which contains 1 foot 8 inches of good coal capped by 6 inches of carbonaceous shale. A bed of coal about 2 feet thick is expQ3ed about 1 mile farther southeast along the outcrop.

The only mine in the northern part of the field which is operated, even at intervals, is located on the east side of Cottonwood Creek, about miles south of the crossing of the Worland-Tensleep road. The opening is at least 50 feet deep and widens out irregularly, but the extent of the development could not be determined because of the quantity of water in the mine at the time of examination. A section measured near the entry is shown by No. 3 on the map (PI. XII). The bed is a lens in the lower part of the Fort Union formation. Valley wash covers the outcrop a short distance west of the mine and the bed is only a few inches thick one-fourth of a mile to the east. Some coal from this mine has been burned by ranchmen in the valley of No Wood Creek and plans have been made for its further development.

The most important mine in the area south of Tensleep Butte is in the badlands at the head of the north fork of Bud Kimball Draw, in sec. 33, T. 46 N., R. 89 W. More coal has been taken from this mine than from any other in the southeastern part of the Bighorn Basin. A section of the bed at the mine is shown by No. 4 on the map. The mine consists of an irregularly widened entry about 75 feet deep. Owing to its mode of weathering, the coal is classed as subbituminous. It has a pitchy luster, medium hardness, and subcubical jointing or cleavage. It contains small nodules of amber-colored resin and thin bands of mineral charcoal. It is probably a noncoking coal and does not stock well. The chemical properties of the coal are shown by analysis 6709, on page 183. The coal is in the Fort Union formation, and, like most of the beds in the field, is lenticular. One-fourth of a mile to the northeast the bed contains only 6 inches of coal, and an equal distance along the strike to the southeast an exposure shows an 8-inch bed included in carbonaceous shale. Although there is suflBcient coal in the bed to furnish considerable fuel for local consumption, development has been prevented by the distance to settlements and the difficulty of maintaining wagon roads for transportation.

About miles south of the mine on Bud Kimball Draw there is an exposure of a coal bed at the base of a small isolated hill northwest of North Butte. The body of coal at this place is about 1 acre in extent and forms an outlier of a lens which originally was thinner toward the northwest, but now a dry coulee cuts the west side of this outlier. Where the bed is exposed across the coul6e, it contains only 18 inches of coal at the thickest place. A section of the coal bed, shown by No. 6 on the map (PI. XII), was measured in an open-pit

180 CONTBIBUTIONS TO ECONOMIC GEOLOGY, 1908, PABT n.

mine on the west side of the hill, where the most favorable conditions for working the coal are found. The small extent of the bed at this place and its thin cover make it impossible for this mine to be more than a small country bank. A few tons of coal have been mined at this place by ranchmen and hauled over the divide road to the valley of No Wood Creek for fuel, but the coal is so dirty and the distanc/e so great that the effort is scarcely repaid.

There are several coal beds in the upper member of the undifferentiated Montana where it is exposed east and northeast of the " Honeycombs/' in T. 45 N., R. 89 W. Section No. 5 was measured a short distance north of the wagon road leading from the mine northwest of North Butte to No Wood Creek. The coal is subbituminous and occurs as a lenticular deposit. An entry driven into the bed in any direction may show an increasing or a decreasing thickness of coal, depending on whether the entry is driven toward the center of the lens or toward its margin. The locality is not favorable for mining.

A lower formation (the CI overly of Darton), which is exposed to the east and dips under this field, contains a bed of coal where it is exposed in the valley of No Wood Creek, on the ranch of Dr. G. H. Walker, in sec. 29, T. 48 N., R. 89 W. The coal occurs as a lens, which extends for less than one-eighth of a mile along the outcrop. When examined in July, 1908, the mine was filled with water and an examination of the unweathered coal was impossible. At the mouth of the mine there is 2 feet of coal in a thick bed of carbonaceous shale. The bed is reported to be much thicker below the surface and this is probably true, because of the lenticular nature of the bed and the crossbedded condition of the rocks above it. An opening was first made in this bed twelve yoai ago, and since then coal has been mined periodically. Mr. Diehl, who owns the property jointly with Doctor Walker, estimates that 2,000 tons have been taken out. The owners expect to reopen the mine and produce coal for the local ranch trade. The Cloverly formation does not outcrop in the area covered by this map, and in adjoining areas cursory observation and the reconnaissance by C. A. Fisher show that it contains only a small amount of coal.

The southern part of the field from the head of No Water Creek to Bighorn River contains more coal than the northern part, but owing to the lack of water and the entire absence of settlers there has been little development. Sections of coal beds measured at various points in the No Water area are shown on the niaj).

The only mine which has been opened in the Xo Water district is about 1 mile northwest of creek, near the wagon road, about 3 miles southwest of South Butte. A section of the bed is shown by No. 7 on the map. The beds dip 23° N. The mine consists of an entry about 100 feet long with no side entries or rooms. The coal

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Poal In S0Uthea8Tebn Pabt Of Biohobk Basin, Wyoming. 181

seems to be subbituminous and of excellent grade. . It is pitchblack with a vitreous luster, has a conchoidal fracture, and appears to slack slowly on exposure. A sample of the coal from this opening was analyzed nth the result shown by Xo. 6708 in the table on page 183. About 150 tons of coal haye been mined and the conditions at the mine are favorable for more extensive development , but its isolation in an uninhabited region wJ;Lich can be reached only over poor roads will probably prevent extensive working for some time to come. Along the strike to the east the bed is concealed for more than a mile, but where it reappears the dip is steeper and the coal bed is considerably thinner. West of the mine the coal bed dips less steeply and is more favorably situated for mining.

Coal is found on the east side of Bighorn River in the same formation that contains the beds mined at Gebo and Crosby, west of the river. The dip of the beds in this area is only 10°, which is less than it is farther west. Two coal beds separated by 22 feet of sandstone and shale are exposed in the low hills north of the valley of Kirby Creek, east of Bighorn River. These beds have been prospected at a number of places with verj promising results and some coal has been mined for local markets. It is probable that the cheaper production of coal by the large companies west of the river has prevented further development, because they supply the only market open to the area that lies east of the river. The coal is of the same quality as that west of the river, but probably the betls are not so thick. The region is traversed by small coul6es, along which roads can be constructed easily and railroad grades leading to mines would be moderate. There is no doubt that as the coal beds west of the river become exhausted the coal to the east will be developed.

Character Of The Coal.

The coal of this field has the same general physical properties as that from other fields in the Bighorn Basin at corresponding geologic horizons. It is of pitch-black color, vitreous luster, cubical jointing or cleavage, and moderate hardness, and shows a dark-brown powder or streak on glazed paper. Small nodules of amber-colored resin are abundant. Sulphide of iron forms little flat disks along the joint planes, but seems to be absent in the body of the blocks. Minute seams parallel to the bedding planes are more higlily bituminous than the body of the coal and when broken produce thin but highly vitreous and shiny bands. The coal appears to stock well, but from samples exposed at the mines it is thought that this property is apparent rather than real. It is probably explained by the dryness of the mines and is due to the condition which arises when dry coal is exposed. Very little moisture finds ready escape, the coal does not

182 CONTRIBUTIONS TO ECONOMIC GEOLOGY 1908, PART n.

shrink much or unequally, and the blocks do not fall to pieces as soon as wet blocks of coal, which lose moisture rapidly.

The coal weathers on dumps to brown, slightly fissile, irregular grains, but where longer exposed to slower weathering becomes a fine brown powder resembling carbonaceous shale. So close is this resemblance that it is difiicult to determine on surface exposures the line of separation between the coal bed and the associated carbonaceous shale. Fragments no larger than half an inch in diameter, though weathered outside,* generally contain less altered material within, which shows some of the properties of the unweathered coal in the bed.

There were only two places in this field at which samples for chemical analyses could be taken, where the coal had been exposed recently below the zone of weathering. These two points were the mines on Bud Kimball Draw and on No Water Creek. Samples were taken at these mines by selecting a representative face of coal, freeing it from powder stain and surface impurities, and cutting a channel across the face about 1 foot wide and deep enough to yield 5 pounds of coal per foot of thickness of bed. From this cutting partings and binders more than three-eighths of an inch thick were rejected. The sample was then broken to pass a inch mesh sieve and then repeatedly quartered, the opposite quarters being rejected until a small representative sample was obtained. A galvanized-iron can holding about a quart was filled from this sample, sealed with adhesive tape, and forwarded te the chemical laboratory for analysis. The table below shows the result of analyses of coal samples from this field and from the Gebo field west of Bighorn River.

COAIi IN BOUTHEASTEBN PABT OF BIGHOBN BA8IN, WTOMlltO. 183

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184 Contkibutions To Economic Geology, 1908, Pabt U.

6708. The coal for this analysis was dug at the bottom of a slope about 100 feet long, at a point where the cover is nearly 75 feet thick. The face had been exposed to the dry air of the region for several months previous to sampling. This condition probably has produced oxidation and a lower moisture content than will be found where the mine is extended to a depth of several hundred feet.

6709. This sample was taken in a dry unoperated mine 75 feet from the mouth of the entry and under about 50 feet of cover. Though the twice from which the sample was taken had been exposed for several months, there was no evidence of weathering, but probably some change had taken place due to the action either of water percolating from above or of dry air absorbing some of the moisture. The coal was dry and the mine dusty; consequently, the analysis probably shows the result of oxidation and less moisture than will be found when the mine is extended deeper.

6707. The mine from which this sample was taken is not located in the field described in this report, but is 2 miles farther west across Bighorn River. This analysis is introduced because the sample is believed to be fodrly representative of the unweathered coal in the Eagle (?) sandstone. The sample was taken at a point 615 feet down the slope from the main entry, where mining was progressing at that time at a depth of about 150 feet below the surface, and the coal seemed to be entirely un weathered.

The coal bums with a yellow flame and only a small amount of smoke. The ash ia fine and does not clinker badly.

The coal is best adapted for domestic use, though with proper grates and drafts it can be used for steaming purposes. It is too light and slacks too readily to give the highest eflBciency imder forced draft, because in such fire boxes small particles of the coal are blown from the fires before they have a chance to bum.

In stoves the coal bums freely with a quick heat and little smoke and does not clinker. It slacks readily but may be kept in small quantities for a long time; so that this property is not objectionable at present, because the local ranch men usually mine only a few tons at a time.

Amount Of Coal Available.

It is difficult to estimate the amount of coal in this field, owing to the uncertainty which the occurrence in lenticular beds gives to such computation. Any estimate may be as much as 25 per cent too small or too large. The northern part of the field contains a little coal in very irrecrular lenses. As the badlands to the west of the Cottonwood Creek and Bud Kimball Draw districts form a barrier to any market except that of the ranchers along the valley of No Wood Creek, it may be stated that in this part of the field there is coal to furnish sufficient fuel for many years if the mines are properly laid out and maintained, but the present unscientific, wasteful methods will greatly shorten the period of profitable production. The southern part of the field contains more coal than the northern part. It is estimated, on the assumption that the coal has a specific gravity of 1.3, that there are 62,000,000 tons of coal in this region in beds more than 3 feet thick and less than 2,000 feet deep. It is

COAIi IN SOUTHEASTEBN PABT OF BIGHOBN BASIN, WYOMING. 185

impossible to mine more than 75 per cent of this amomit by present mining methods; hence not more than 46,500,000 tons are available as a future source of supply.

Market.

It has been stated that market conditions are imfavorable except for a small area in the extreme southwestern part of the field. The coal must be hauled by wagon at least 10 miles over rough roads and much of it a considerably greater distance. The demand is for fuel on ranches, as no towns are near enough to afford a market. The coal to the southwest near Bighorn River is within a few miles of a railroad, where it can be marketed now by hauling a short distance by team. It can be reached by a short railroad spur when the coal is in sufficient demand. The only competing fuel in the field is wood, which is not abundant.

Future Development.

It is expected that the area of coal near Bighorn River east of Kirby will receive attention from miners as soon as the coal to the west becomes a little more difficult to obtain. Elsewhere in the field the conditions are not promising for future development beyond the Tnining of a few tons each year by local ranch men who can overcome the difficiilties of haulage. Further, owing to poor land surveys the coal areas can not be segregated and valued ; hence title to them can not be obtained from the Government imtil a resurvey is made. These conditions will delay development.

The Eastern Part Of The Little Snake River

Coal Field, Wtoming.

By Max W. Ball and Eugene Stebinger.

Introduction.

The Little Snake River coal field includes an area of about 1,150 square miles, approximately 900 square miles of which is in Carbon and Sweetwater counties, Wyo., and 250 square miles in Routt County, Colo. It is separated from the Yampa field on the south by the crest of the Elkhead Mountains, and from the Great Divide Basin field on the north by the watershed between the Pacific drainage and that of the Great Divide Basin. It was first mapped geologically by the King Survey in 1871-72. In 1902 the part of the field lying generally north of Little Snake River and east of Battle Mountain was included in Spencer's map of the Encampment copper district.* The Wyoming portion of the field has been the subject of two seasons' field work with especial reference to coal. During the summer of 1907 a party consisting of Max W. Ball, B. L. Johnson, J. T. Singewald, jr., J J. Reinecke, Robert D. Sawin, and Ray D. Sawin surveyed the area north of Little Snake River and west of a line passing through Dixon, Five Buttes, and Bridger Pass, including that portion of the Great Divide Basin which lies south of the Union Pacific Railroad. In the season of 1908 a party comprising Max W. Ball, Eugene Stebinger, C. L. Baker, and Arthur M. Douglass completed the mapping of tlio Wyoming part of tlie field, as well as of a few small areas in Colorado nortli of Little Snake River, and in addition made a further study of some of the area examined during the previous season. This [)a[)er is a brief report of the results of the investigations of 1908 and of necessity duplicates or revises, both in map and text, many of the statements pi-esented in the preliminary* paper on the western part of the field.'*

A. r.. vloinslts of KncAinpment district. Wyomlag: Prof. Paper U.S. Geol. Survey

h UiUl. M. W.. Tho wtvttorn part Little SnAkv Kiver coal field. Wyomlnc: BuU. U. 8. Geol. Survey No. 341. 1*15>. pp. 'J43-iVv,

BASTBBN LITTLrE SNAKE RIVEB COAL FIELD, WYOMING. 187

The mapping in the field was done on a scale of 2 inches to the mile, with contour intervals of 100 feet. A few small areas were sketched by plane-table methods, but the greater part of the work was done by pacing land Unes on horseback from section comer to section comer, each comer found being used as a new and correct location for continued work. The horizontal control of the map thus depends largely on the presence of land corners, and the location of features with respect to land lines is accurate in proportion to the number of monuments found. North of the fourth standard parallel north comers are rather numerous and easily discovered ; south of that line they are relatively scarce. E. Lambert, as county surveyor, established comer stones in most of T. 16 N., R. 92 W., and in portions of T. 15 N., Rs. 91 and 92 W. From the township comer just southeast of Five Buttes a Une of original comers extends 3 miles west; another runs possibly 3 miles south; about one-third of the original comer stones are present for 6 miles on the line north ; and a line of unmarked stones continues 3 miles east. A number of comer stones were found in T. 12 N., Rs. 89, 90, and 91 W., and T. 13 N., Rs. 90 and 91 W., and a very few in T. 14 N., R. 89 W.

In the summer of 1907 a line of levels was run diagonally across the field from a United States Coast and Geodetic Survey bench mark at Rawlins, on the Union Pacific Railroad, to Baggs, bench marks being set about every 3 miles from Rawlins to Muddy Bridge and two between Muddy Bridge and Baggs. From these bench marks and from those in the area east of Battle Mountain estabUshed during the topographic survey of the Encampment special quadrangle in 1901, flying levels were carried by telescopic ahdade and stadia to the various temporary camps of the party, furnishing control for the aneroid and hand-level altitudes used in sketching.

From the field sheets a complete contour map on a scale of 1 inch to the mile was compiled in which the lengths of the land lines as given by the oflScial Land Office surveys were accepted as correct and were plotted by so balancing the recorded distances about a vertical and a horizontal right line intersecting near the southeast corner of T. 16 N., R. 91 W., that the distortions due to convergence of meridians and errors of survey are theoretically distributed equally over the sheet. As a result of this balanced plotting of the recorded lengths of land lines rather than their bearings, the length of the sides of any particular township or section is the same as*that given on the corresponding Land Office plat, but the shape of the township or section may be different from the shape shown on that plat. From the contour map, by reducing the scale and eliminating everything but the more important drainage and cultural features, the base was prepared for the accompanying map (PI. XIII), on which are indicated the different geologic formations in the coal area, the

188 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1908, PART n.

of the principal coal openings, and such other geologic facts as have a direct bearing on the occurrence or development of the coal. No attempt is made to show the subdivisions of the geolcc column except in the coal-bearing part.

There are represented in the field and its vicinity sedimentary rocks down to the Beds" of the Triassic, but neither the formations below the Mesaverde nor the igneous rocks upon which the "Red Beds" rest unconformably are indicated on the map. All the beds nbove the Upper Laramie," including the Wasatch and later Tertiary formations and part of the alluvial deposits are shown by a single pattern.

Acknowledgment is due to a large number of persons in the field who in person and by correspondence have facilitated the work through information given and courtesies extended.

Surface Features.

The Little Snake River coal field presents every topographic gradation from the heavily timbered slopes of the Elkhead Mountains and Sierra Madre to the alkali flats of the Red Desert. Little Snake River, in the drainage basin of which the field lies and from which it takes its name, originates in the confiuence of three tributary streams a short distance east of the coal field and crosses it in a course trending almost directly west through a fertile flat-bottomed valley from half a mile to 2 miles wide, flanked here and there by benches or mesas whicli increase in number toward the western margin of the field. Immediately north of the river in the eastern part of the field the lava-capped eminences of Sheep Mountain, Mule Mountain, Horse Mountains, and, highest and most prominent. Battle Mountain, overlook abruptly a great plateau extending eastward to the base of the Sierra Madre and northwestward to Browns Hill and Five Buttes. In this comparatively level upland Savery and Battle creeks and their tributaries have cut precipitous canyons, whose bottoms in many places are ricli agricultural land. The regularity of this upland is interrupted in the vicinity of Browns Canyon and Rubey Springs by a higher mesa, with white escarpment faces. North of this higher mesa, toward Sulphur and Bridger Pass, the upland loses most of its plateau characteristics and becomes a series of high ridges with toward tlie east and dip slopes toward the west. Muddy Creek crosses tliis highland in a deep, narrow canyon known as the Upper Narrows of the Muddy, and its headwaters have hollowed out a valley called Muddy Basin between the eastward-facing cliffs and the higher mesa that extends northward and eastward from Rubey Springs. West of the plateau is a depression, in places a simple valley, elsewhere a broad area of low, irregular relief, terminated on the west by

Eastebn Little Snake Biveb Coal Field, Wtominq. 189

a series of hogbacks and transverse ridges, with a few high points such as Muddy Mountain. In the area described in this paper the western limit of the hogback region is marked by a brilliantly colored escarpmenty which constitutes approximately the western margin of the coal field and the eastern border of a great, almost waterless area of badlands, broken dip slopes, and isolated buttes locally known as desert." Along the face of this scarp from the old Washakie stage station southward Muddy Creek meanders through a flatbottomed valley to its junction with Little Snake River at Baggs.

Geology.

Structure.

The geologic structure of this area is dominated by the uplift of the Sierra Madre just east of the field. The attitude of the coal-bearing formations varies from horizontahty to a dip of 35°, the dip being generally greatest near the western margin of the area. The direction of dip is slightly west of north in the north end of the field and swings through due west to southwest in the vicinity of Little Snake River. Along this river above Savery Creek there are many minor folds which produce dips of as much as 4° in every direction and give to the outcrop of the lowest coal-bearing formation, the Mesaverde, a width of approximately 15 miles, as compared with 3 miles, both in the vicinity of Bridger Pass, near the north end of this field, and at Wolf Mountain, in the Yampa field. The dips of the beds overlying the coal-bearing formations are uniformly low. The Wasatch dips generally from 1° to 4° W., although in places it has a higher dip immediately in contact with the older beds ; the Bishop ( ?) conglomerate (Tertiary) is either horizontal or dips 1° or 2° E.

Only one fault of any magnitude was observed in the field. This crosses the river in sec. 16, Wyoming, and sec. 17, Colorado, T. 12 N., R. 88 W. Its throw could not be ascertained, but probably is not less than 50 feet. The location is within a mile and a quarter of the highest point on Battle Mountain, which is probably, like its neighbor, Sheep Mountain, the site of the vent whence issued the basalt now forming its cap.

Stratigraphy. General Section.

A section of the rocks of the field from the Sierra Madre westward would give an incomplete succession of the formations from the pre-Cambrian upward. In the following table the general char-

FenneiiMO, N. H;, and Gale H. 8., The Yampa ooal field, Routt County, Colo.: Bull U. S. GeoL Sor- ▼ey No. 297, UOft.

190 Contbibutions To Economic Geology, 1908, Pabt Ii.

acter and approximate thicknesses are given for only the coal-bearing and associated formations:

Generalized section of coal-bearing and associated rocks in the southern part of the Little

Snake River coal fields Wyoming.

System.

Formation.

Thickness (feet).

Bishop ( T) conglomerate.

U nconformlty

4)

a

H

Wasatch formation.

Unconformity 1

"Upper Laramie" formation.

1,000±

Top not seen.

Characteristics.

White to light-gray calcareous sandstone and sandy limestone north of Bird Gulch; yellow to white beds of poorly consolidated sand and gravel in south end of field. Basal conglomerate.

Variegated clay , passing upward into brown and gray shales, sand, and sandstone. Highlv calcareous conglomerate at oase in some pcu-u of field.

4(

Laramie" formation.

0 to 4,000.

3,500.

a

Lewis shale.

1,G00.

o

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up.

o

o

es

Mesaverde forma- 2,000.

es

tion.

a

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'1

Gray and brown sandstones and grav and drab shales, with many coal beds.

White to dark clay shale.

Heavy sandstone, with Interbedded shale and numerous beds of good coal; conglomerate at base.

Brown and gray shaly and concretionary sandstones and dark shale, with several beds pf coal. In parts of the field the lower half is yellow, softer, and more sandy, and apparently contains less coal than the upper half.

Drab, slightly sandy, highly gypsiferous shale, with a few beds of thin soft sandstone.

Upper two-thirds alternating sandstone and shale beds, with heavier sandstone beds in upper part. Bottom third made up of massive cross-bedded sandstone with some Interbedded shale.

Dark-drab concretionarv calcareous shale, with several thin beds of soft brown sandstone.

Coal resources.

Not coal bearing.

Not coal bearing.

Coal bearing throughout except in white to dark day shale member. Bottom part contains coal beds.

Contains some ooaL

Not coal bearing.

Upper two-thirds contains many coal beds and principal mines in the field. Bottom third not coal bearing.

Not coal bearing.

Montana Group.

Shale.

Immediately underlying the lowest coal-bearing formation in this field is a non coal-bearing shale, the equivalent of the upper part of the Mancos shale as mapped and described in western Colorado. It has a thickness of not less than 2,000 feet, is dark drab in color, weathers almost white in places, is somewhat concretionary and very calcareous, and contains numerous thin beds of soft brown sandstone,

ZAffXt&S LITTLE SNAKE BIVEB COAL FIELD, WTOMINQ. 191

especiall/ near the top. A particularly persistent sandstone which has beetf observed throughout this field, the Great Divide Basin, and the eaitkntral Carbon County field, occurs about 200 feet below the base (n the Mesaverde, and as the dips are high or low forms either a hogblUk or a secondary scarp a short distance out from the foot of the Mesaverde escarpment.

Mssavbrde Formation.

The Mesaverde formation may be divided readily, though not definitely, into three practically equal parts. The lower third is made up of massive white, gray, and rusty-brown cross-bedded sandstone, with some interbedded shale and shaly sandstone. North of the Up[>er Narrows of the Muddy a bed of limestone 25 feet thick was observed about 150 feet above the base of the formation. The line of demarcation between this lower member, which is not coal bearing, and the underlying shale is not everywhere distinct. Near Standard Headquarters on Savery Creek the transition is marked for 300 feet or more by an alternation of beds of heavy sandstone 2 to 50 feet thick, with beds of drab, white-weathering shale 1 to 30 feet thick. The upper two-thirds of the formation is composed of alternating thin-bedded and shaly sandstones, gray, brown, and drab shales, and a few beds of massive sandstone that increase in number toward the top of the formation, so that where the beds are tilted the upper and lower members of the formation stand out as high ridges and the middle member occupies a depression between. In the southeastern part of the area shown on the accompanying map (PL Xni), where the beds are nearly flat and are covered by the Bishop ( ?) conglomerate, the Mesaverde produces a great plateau with deep canyons. The middle member is coal bearing in the south end of the field, containing the Carbondale (1), Stemp Springs (2), and probably the Linde (3) and Lucksinger (4) mines. Toward the north the coal beds become less numerous, thinner, and dirtier. In a section across the formation at the Upper Narrows of the Muddy no coal was found in the middle member, although the outcrop is covered in a few places and may contain coal beds. The upper member contains a number of coal beds throughout the field, the Robertson (16), Angier (7), Darling (6), Martin (5), O. P. Beeler (18), and possibly the Lucksinger and Linde openings being on coal beds in this member. The following section through the Upper Narrows of the Muddy just east of Sulphur shows the location, number, and thickness of the coal beds in the upper member in the northern part of the field :

Numbers refer to locations on XIII,

192 Contributions To Economic Geology, 1908, Part Ii.

Section of a part of the Mesaverde formation north of Muddy Creek in Tps. 17 and 18 N.,

R. 90 W., Wyoming.

Thickness.

shale, chocolate or drab, thin-bedded sandstone and coal, approximately... . Sandstone, thin bedded, baff, somewhat reddened by heat, with small amount of shaie.

Sandstone, thin bedded

Shales, black, carbonaceous, and brick-red, giving evidence of a bamed coal bed

Sandstone, thin bedded, buff, with thin streaks of buff shale

Shales, bituminous and drab

Coal ( Robertson opening)

Shales, bituminous and chocolate drab

Sandstone, thin bedded, buff

Coal...

Sandstone, thin bedded, buff

Shale, drab, with thin beds of coal

Coal, at least

Shale, chocolate or drab, with thin beds of coal

Sandstone, massive, buff

Shale, dark, with abundant plant remains and at least six beds of poor shaly coal less than 1 foot thick

Coal :

Covered

Sandstone, thin bedded, buff

Shale, dark brown

Sandstone, massive, buff

Coal

Shale, black

Sandstone, massive, buff

Distance from base of formation.

FeH.

Feet.

1,973

1,673

1,643

1,583

1,569

1,558

1,548

1,504

1,503

1,474

1,467

1,428

5

1,406

1,401

1,386

1,371

Lack of continuous exposures makes it impossible to tell whether or not individual beds of Mesaverde coal extend continuously for long . distances. Some of the prominent sandstone ledges of the lower part of the formation may be traced for many miles, but the sandstone beds of the coal-bearing members of the formation do not appear to be so persistent. It seems probable that the beds are more or less lenticular and that in general where one bed thins out and disappears another one is present, so that the number of beds remains about the same and the coal maintains an approximately constant aggregate thickness, but no one bed is continuous over a great area.

Lewis Shale.

The Lewis shale is soft, dark drab to black in color, and highly gypsiferous, with a few beds of soft shaly sandstone that increase in number toward the top of the formation. The sandstone varies in color from white to rusty brown, and the shale is slightly more sandy near the top of the formation than it is lower down. The shale weathers rapidly, producing between the highlands of the Mesaverde, on the one hand, and the less prominent 'Laramie'* hogbacks, on the other, an almost continuous valley, or series of valleys, of which advantage has been taken in locating a great part of the Rawlins-Baggs stage road (formerly the government road from the

Eastern Little Snake Riveb Coal Field, Wyoming. 193

Union Pacific Railroad to the White River Indian Agency), as well as a number of other roads. No coal was observed in the Lewis shale in this field.

'*laramie" formation.

The Laramie" formation is made up of interstratified beds of gray, buff, and rusty-brown sandstone, and gray, brown, drab, and black shale. The sandstone as a rule is thin bedded, but some beds are massive and a few are concretionary. In some parts of the area, notably along Cherokee Creek, there is a marked difference between the upper and lower parts of the formation, the sandstone in the lower half appearing more shaly and less consoUdated and the shale zones more numerous and sandy than in the upper half. The result is a sandy shale member with a few beds of resistant sandstone about midway in character between the normal upper part of the formation and the underlying Lewis shale. In the northern part of the field the formation is uniform throughout, the base of the formation as mapped being a massive white sandstone,* which as a rule forms either an escarpment or a prominent hogback. At Muddy Mountain, south of Cherokee Creek, the lower half of the formation seems to be even more resistant than the upper, with a greater percentage of indurated sandstone.

The Laramie" formation is undoubtedly coal bearing throughout the Wyoming portion of the field, but the number, thickness, and relative location of the coal beds could not be definitely determined in the area treated in this paper, owing to the prevalent cover of hill wash over the formation and the fact that most of the coal beds do not occur between beds of sandstone but in shale that weathers rapidly and hence produces a minimum of exposures. In the field no mines are located in the Laramie" and only one prospect, that in the SW. J NE. J sec. 15, T. 12 N., R. 90 W. (No. 8), opposite the Deary ranch. Owing to the presence of valley filing, river terrace, and Tertiary deposits several miles in extent between this location and the nearest Laramie" exposure to the north, the reference of even this coal bed to the Laramie" is a matter of no great certainty.

''upper LARAMIE " FORMATION.

The lowest member of the ' 'Upper Laramie " formation is composed of beds of gray and brown sandstone, with intercalated gray, brown, and drab shale and numerous beds of coal. The beds of sandstone

a This mapping is based on the fact that the formation from the bottom of this sandstone upward is a Uthologic unit. Paleontologically the formation probably begins some 400 feet higher, as marine Montana fossils have been found to that distance above the massive sandstone, thus associating the lower 400 feet of the formation as mapped with the Lewis shale.

7963**— Bull. 381—10 13

194 Contributions To Economic Geology, 1908, Pabt U.

are thicker, more numerous, and more massive toward the base, which is marked by a bed that is extremely massive, cross-bedded, in many places highly ferruginous, and as a rule somewhat conglomeratic. The pebbles are composed of well-rounded crystalline and cryptocrystalline materials, chert predominating, and as a rule they are small, but lenses of conglomerate with pebbles up to 18 inches in diameter appear locally. In the southern part of the field a basal conglomerate is present, in places in contact with or forming a part of the massive sandstone. In other places, notably just east of the Standard ranch on Muddy Creek, the basal conglomerate is represented by two beds, each about 8 feet thick, approximately 100 and 200 feet below the massive sandstone and separated from it and from one another by dark shale. The pebbles are mainly chert, held in a matrix of chert and crystalline quartz grains about the size of coarse sand.

On the coal beds of the lowest member are the Muddy Bridge opening, the openings in Coal and Cutoff gulches, northeast of Baggs, and a number of other prospects. The individual coal beds appear to be continuous for long distances. An idea of the lithologic character, number, and position of the coal beds may be gained from the following section taken along the Lower Narrows of the Muddy near the old Washakie stage station. Farther south some of the beds are thicker than any shown in this section.

Section of a part of the Uppcr Laramie* formation near old Washakie Mtage station, north of Muddy Creek, in Tps. 11 and IS N., R. 91 ir., Wyoming.

Feet.

Shalo, brown 70

Sandstone and burned coal bed, inlet'ely red 20

Covered mainly; where exposed brown, black, and gray shale, with

thin-bedded brown tjandstone 80

Sandstone, nias'ive and thin bedded, yellow 50

Shale, brown 8

Coal 5

Sliah\'. yellowish and brown, with shaly sandstone 61

Shah', ypsiieroiis, with thin coal beds 10

Sandstone, haly and thin bedded, yellow and brown, with brandy

shale 33

Shale, 'ypsiferniis. black 3

Coai 5

Shale, siuuly. liirht >:ray 5

ihin leddcd, yellow 6

impure 7

Shale, saiidv, vellowi.sh brown 4

( 'oa 1 2

Shale, ixniy 5

Shale, sandv and Ncllowi.-h brown, shalv sandstone 10

Eastebn Little Snake Biveb Coal Field, Wyoming. 195

Shale, bluiab gmy, with plant remaiBs 4

Coal, burned in places 5

Covered; creamy sandstone near middle, brown shale at top 344

Sandstone, cross-bedded, conglomeratic, grayish and light bniwn... 25 Sandstone, buff, conglomeratic. Small pebbles of diabase, chert, and crystalline quartz scattered sparingly throughout except near top, which is full of pebbles one-fourth inch to 18 inches in diameter, with evidences of local unconformity 80

Overlying the lowest member of the Upper Laramie" is a non coal-bearing member, consisting of clay shale and sandy clay, with a small amount of soft sandstone, either massive or thin bedded. In the northern portion of the field the clay is almost pure white, whereas in some of the exposures near the river it is dark drab, bordering on black, with rare tinges of red, which may have been leached from the adjacent Wasatch. The beds of sandstone in this member, which are extremely varied in number, thickness, and location, are as a rule gray. Throughout the greater part of the area the member appears to be free from conglomerate, but in many places between Cherokee Creek and Deep Gulch large quantities of rather coarse cherty conglomerate are present. Although this clay shale member is easily and definitely recognizable wherever exposed from the Union Pacific Railroad to its disappearance under the Wasatch just north of Little Snake River, its thickness seems to vary markedly through lithologic encroachment upon it of the underlying and overlying members.

The uppermost member of the Upper Laramie" is composed of gray and brown sandstones with interbedded shale. Some of the shale beds closely resemble those of the clay shale member, from which the upper member is, however, distinguished by the greater number and superior resistance of its beds of sandstone and by the presence, where exposures are satisfactory, of numerous beds of coal. In the area specifically treated in this paper outcrops of tliis member are not numerous, owing to the overlapping of the Wasatch formation, which through most of the area covers it completely. The coal beds of the member have not been carefully prospected, although from Riner, on the Union Pacific Railroad, to Coalbank Spring,* the beds are very prominently exposed.

Regarding the geologic age and the equivalence of tliis formation there has been some uncertainty. It doubtless constitutors the earliest Tertiary deposit of the area, and from paleobotanical evidence F. H. Knowlton now considers it to be of Fort Union age. The formation as mapped is the equivalent of the '*U|)per Laramie"

Ball, M. W., The western part of the Little Snake River coal field, Wyoming; Bull. U. S. Geol. Survey No. 341, 1909, Plate xm.

196 Contkibutions To Economic Geology, 1908, Part Ii.

of Veatch in the Hanna field, where it is separated from the Laramie" Lower Laramie" of Veatch) by a great unconformity. This unconformity was also observed by Smith in the Great Divide Basin north of the Union Pacific Railroad, but though evidence of local unconformity appears in one or two places, no general unconformity was observed in the Little Snake River field. In sees. 25 and 26, T. 13 N., R. 91 W., a few isolated exposures were found with strikes trending much more toward the east than any of the underlying formations, but the cover of Wasatch and later deposits southward to the state line made it impossible to determine whether these exposures represent a local fold or a definite trend of the formation which could only be accommodated by its unconformably overriding some of the older beds.

Wasatch Formation.

The Wasatch is separated from the underlying formations by a pronounced unconformity. West of the old Washakie stage station the base of the formation rests on the upper member of the "Upper Laramie." South of the Standard ranch on Muddy Creek it rests on the lowest member of the "Upper Laramie." From this point south it oscillates between these two positions as far as the Dixon Cutoff, where it swings abruptly eastward and overlaps the formations down to the top of the Mesaverde. The Wasatch formation is composed mainly of rather sandy clay, with a few beds of shale and soft sandstone, the latter mostly massive and in places finely conglomeratic. Higher in the formation the proportion of clay to shale decreases, the beds of sandstone increase in number, and the sandstone is thin bedded and more resistant. The usual coloring of the clay, which is roughly bedded, is brilliantly banded red and white, although purple, green, drab, and yellow colors are common, and in places, notably along the north bank of Little Snake River just below Dixon and the south bank just above that point, the color is almost entirely leached out. Locally the shale partakes of the brilliant coloring of the clay but as a rule it is green, yellow, brown, and drab and the sandstone is gray and rusty brown. As the proportion of clay decreases toward the upper part of the formation tlie red color becomes less prominent, appearing here and there in a diminishing number of isolated patches, until the formation is ahnost entirely composed of wliite, gray, brown, and drab shales and clays, with a number of thin bedded gray and rusty brown sandstones. In some places it is difficult to distinguish

o Verttrli, A.(\, Coal of rast-central Carbon County, Wyo.: Bull. U. S. Geol. Survey No. 316, 1907, pp. 244

6 Smith. K. i:.. Tho (in-at Dlvltle coal fMld, Wyoming: Hull. V. S. Cieol. Survey No. 341, 1909, pp. 224, 233.

Bastebn Little Snake Riveb Coal Field, Wyoming. 197

at first glance between the uppermost part of the Wasatch and the "Laramie" or the upper member of the ''Upper Laramie/' but a careful search over any considerable area will almost invariably show one or more patches of bright red color. The lowest member of the formation in the region just south of Muddy Mountain seems to be a yellow or white conglomeratic sandstone, in places highly calcareous. The Wasatch is very prominently exposed along Little vSnake River for many miles below Baggs and south of the river in the lower slopes of Black Mountain.

Bishop (?) Conglomerate.

In his mapping of the geology of the Encampment district, Spencer following the usage of the King Survey, adopted the name "Wyoming" conglomerate for the sandstone conglomerate which caps the interstream areas in the southwestern part of the district that he examined, including that part of the Little Snake River field lying north of the river and east of a north-south line along the east base of Battle Moimtain. It is probably the equivalent of the Bishop Mountain" conglomerate of the Powell Survey, now called Bishop conglomerate. The basal conglomerate of the formation covers the greater part of the level upland from the vicinity of Bridger Pass to the river. It is 50 feet or more in thickness and obscurely bedded, with poorly assorted pebbles of all sizes up to bowlders 2 feet in diameter, and with lenses of white and yellow sandstone, rather soft and more or less massive.

Above the basal conglomerate on Sheep and Battle mountains and in the Elkhead Mountains south of the river lie several hundred feet of poorly consolidated sand and gravel. On the north slope of Battle Mountain some of the sand is of extreme fineness, whereas other beds are very pebbly, and on the north face of Black Mountain, south of Dixon, a great thickness of very coarse unconsolidated conglomerate is exposed. In the vicinity of Sheep and Mule mountains the beds are consolidated into a gray massive sandstone, highly cross-bedded, showing mud cracks in many places. On the north wall of Bird Gulch just above Savery Creek (sec. 26, T. 15 N., R. 89 W.) the basal conglomerate is well exposed, lying unconformably upon the westwarddipping sandstone of the Mesaverde formation and dipping slightly northward to Browns Canyon and Rubey Springs, where it apparently forms the base of a series of white sandy limestone and calcareous

sandstone, the westward continuation of the formation which Veatch**

a Spencer, A. C, Copper deposits of the Encampment district, Wyoming: Prof. Paper U. S. Geol. Survey No. 25, 1904.

Veatch, A. C, Coal fields of east-central County, Wyo.: Bull. U. S. Geol. Survey No. 316, 1907, Plate XIV.

198 OONTBISnTIONS TO ECONOMIC QEOLOOYy 1908, PABT IL.

mapped near Platte River and elsewhere as North Park. It thus seems highly probable that the Bishop ( ?) conglomerate is a phase of the North Park Tertiary, differences in lithology being produced by different sources of materials, closer proximity to those sources, and somewhat different conditions of deposition.

Eruptive Rocks.

Battle, Sheep, and Mule mountains and the Horse Moimtains are covered with lava caps from a few feet to 300 feet and more in thickness. One vent from which the eruptive mass issued was located on Sheep Mountain. Probably Battle Mountain and possibly one of the Horse Mountains also were sites of openings.

Later Deposits.

Along the sides of Little Snake River valley are benches at different elevations, covered by gravel which either was deposited by the river at its former levels or represents remnants of alluvial slopes. The higher ones are difficult to distinguish from the apparent terraces formed by the lowest beds of the Bishop ( ?) conglomerate.

The river since reaching its present level has filled with alluviimi the valley through which, with nimierous riffles, it meanders. Its principal tributaries from the north. Battle, Savery, and Muddy creeks, also occupy aggraded valleys in their lower courses. This is especially noticeable in Muddy Creek, which flows tlirough alluvium for nearly 40 miles, the last 25 miles being almost entirely through reworked clay of the Wasatch formation, which has not the fertility shown in the bottom land along Savery and Battle creeks.

In the vicinity of Tlie Willows is a great area of dunes built up by sands brought from the desert by the prevailing southwest winds. Those dunes are traveling toward the Upper Narrows of the Muddy and from present indications may in time partly fill that canyon. A second small sand-dune area exists south of the Standard ranch, on Muddv Creek.

Finally, over a great part of the field is spread a mantle of overwash derived mainly from the beds which it covers, with a sprinkling of igneous pebbles probably left from the erosion of some overlying

The areas covered bv all these later deposits are only partl} shown on Plate XI II.

Bastern Little Snake River Coal Field, Wyoming. 199

The Coal.

Chemical Properties.

The prime object of the survey of this field was the classification and valuation of the coal lands. With this end in view samples of the freshest coal obtainable were taken, but it was impossible to get completely unweathered coal owing to the lack of adequate openings and fresh working faces. The samples are therefore not comparable to many of those obtained in the same formations by Veatch in the Hanna field and by Schultz in the Rock Springs field, where the samples were taken from fresh faces in large working mines.

The coal samples, which were taken according to the method described in Bulletin 341,*' were analyzed at the Geological Survey fuel-testing plant at Pittsburg, Pa. In the table below are given the analyses of all samples taken in the portion of the field represented on the accompanying map, including some which were published in the report on the western part of the field. In addition, to illustrate the character of the Laramie" coal, of which it was not possible to procure an imweathered sample in the field, two previously published analyses of the coals of this formation in neighboring fields are given.

a Veatch, A. C, Coal fields of east-central County, Wyo.: Bull. U. 8. Oeol. Survey No. 316, 1907, pp. 253-258.

frSdiultz, A. R., The northem part of the Hock Springs coal field, Sweetwater County, Wyo.: Bull. U.S. Geol. Survey No. 341, 1909, pp. 270-273. See also paper on the southern part of the Rock Springs field, pp. lOi-171 of this volume.

cCunpbell, M. R., Bull. U. S. Oeol. Survey No. 341, 1909, p. 12.

Ball, Max W., The western part of the Little Snake River coal field, Wyoming: Bull. U. S. Oeol. Survey No. 341, 1909, p. 251.

a

i sini am sAii ss§s sais sss asss

35!=:

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isis ssi; ISS0 ss; ssis :;i ar an

SS i : 55 M N 35 M s: i i n 33 M 3: n

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f.

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£

Eastbbn Iittl£ Snake Biveb Coal Field, Wyominq. 201

§§i§ HsU BSs3 Um §g§§ ilag i§§§ i i

#k Sk flh

5,401 5,528 6,684 7,012

4,843 5,141 6,106 6,977

4,499 4,988 6,919 6,626

4,641 6,322 6,273 6,832

6,762 5,851 6,410 7,198

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202 CONTBIBUTIONS TO ECONOMIC GEOLOGY, 1908, PART n.

Mesaverde Coal.

The Mesaverde formation contains the best coal in the field. Coal from this formation is now being mined in Wyoming at Rock Springs and Superior, and in Colorado in Routt County and from Newcastle to Crested Butte. The Mesaverde coal is probably more easily and economically minable than that of either of the other coal-bearing formations, owing to its prevailing low dips. This advantage may possibly be ofTset in many places by minor faults of a few feet displacement. The coal, which is bituminous, is very hard, rather brittle, with an almost metallic luster and a tendency to conchoidal fracture. The bedding is obscure and there is little or no cleavage. At the Stemp Springs, Carbondale, and Lucksinger openings there is a well-marked series of rifts or slips in one direction perpendicular to the bedding. In a very few places a less distinct system is present which is perpendicular to the bedding and approximately at right angles to the first system. These rifts, of which advantage is taken in shooting down the coal, dip from 65° to 90° and are not evenly spaced or continuous. Many of them show sKckensides, and in the Lucksinger opening a few contain a thin film of pyrite and a very few show one-eighth to one-half inch of crushed coal. The coal is mined and handled with a small percentage of breaking and resists weathering well. A sample from the Lucksinger opening which had laid in an open shed for seven months was black, hard, and linn, with subnietallic luster, no cleavage, slight conchoidal fracture, and no signs of weatliering beyond a certain amount of peacock coloring. In thoroughly weathered surface exposures the coal breaks into rusty-brown cubes 4 or 5 inches on an edge, and these in turn break into very small cubes with black submetallic faces. The general character of the Mesaverde coal beds is shown in the following sections:

Sections of coal beds iu the Mcsarirde formation in the Little Snake River field, Wyoming.

No. on PI.

Location. (Quarter. St.

SK. i \W. 1. al(.

i. ui7

SK. i SW. 7 1 NW . 1. M

n.

si ST

S7

Samlstone, white. Ft.

Coal 1

ShaU'. liituniinous 2

'1

4 +

Xunieof rnineorchar- ' ttc'ter of opening.

i Surface exposure.

Surface exposure.

—

Coal, bottom not ex-

not exposed.

Coal, bailly weathered. 0 Floor not I'xposed.

Coal, 2

I'ire ('lav 4

('arbondale mine.

I Sh-ili

Coal. mhI 2

Surface exposure.

'i Colorado.

EASTEBN UTTLE SNAKE BITEB COAL FIELD, WTOMnrO.

%)u

L4MatkKi.

dl-

BK.iBW-.|.

S. t.Ir.

a

nt w

R. hu

BIE.|KB.i.

SK. I BE. i. SW, I 8K. I.

-u

- Is 3

SUmp SpflniB mine.

u,

Is 8

Be. 1 Sk, I.

fl

Sbtit.

U 8

NE. i NE. 1.

—

I sm

Sw. 1 Nw. 1.

'

Martin mine or Com-

BW. 1 8W. i.

la

Bbalf.bluUh ' 3

BIV. i SE. J- NW. i NK. i-

so

"

(00l,(00d

-a

UK. i >JE, 1.

M

u

Shalt. Shale.

BE.iBW.i. NW. 1 NW. i.

n

~l"

Bbale.

n

Shale.

NW.JSW.i.

Be.1Nw.1.

Coal.'

204 Contributions To Economic Qeologt, 1908, Pakt H.

Section otoottllifd.

Numotmlneaichar-

(iaata.

Sec.

8E. 1 Ne. 1.

is

n. (n.

St

MW.iSW.J.

"

NE. t NE. 1.

U

to

Nw. 1 Ne. 1.

U

Jo

Shmle.

Coal i 3

Emu

Be.1.

Coal, good 11

Bollom noleipowd.

RaberUon miae.

"Laramie" Coal.

As stated in a previous paragraph, it was possible to make only a few observations on the coals of tbe "Laramie" formation in the Little Snake River field, and no samples for analysis were obtained. Where observed, the unweathered coal has a submetallic luster and parts readily along the bedding planes, which are rather prominent. As weathering progresses this tendency to split along the bedding planes increases and vertical joints develop until the coal breaks readily into small plates, with the vertical planes black and lustrous and the horizontal planes yellow or rusty brown.

Sa:lionio/coalbedsinlke"Laramie" fiirnuUitm in tfie Little Snakt Hivrr field, Wyoming.

; Swilonutcoalbed,

Name o( mine or

Coalpgowl

Shale.

Frospert.

Coal, brownish

it

Coal

.. 16+

Siirtofe exposure.

Si.rIar,fjiposure.

cial

1 Bottom not expossei.

10

Eastebn Uttle Snake Biveb Coal Field, Wyoming. 205

"Dpper Laramie" Coal.

The "Upper LarBinie" formation probably contains more coal than any other formation in the held. The coal is of about the same grade as that in the "Laramie," but is of lower calorific power, air slacks much more rapidly, and breaks down more easily in mining and handling than the Mesaverde coal. The nearest point at which it is mined extensively is Hanna, Wyo. The unweathered coal is block in the lowest member and in most of the uppermost member, but in places thin beds of impure coal with a brownish tinge are found near the top of the formation. As a rule the coal is rather light in weight and has a submetallic to resinous luster. Many beds are gypsiferous and a small amount of pyrite is common. It splits readily along the bedding planes and on weathering develops two secondary joint systems approximately at right angles to the bedding and to each other, so that the weathered coal breaks into little shaly blacks, all of whos faces are apt to be coated with a film of selenite ferrous sulphate.

Sectiont of coal btdi in the batal Tnembero of the " Upper Laramie" formation in the

Ucalton.

"kT

Sec.

T.

R.

NE. i NK. 1.

n

Ft. In.

H48

U

Si

Prosptot.

Sm7

NE.jaw.i.

Si

2S

Bone.

Coal

Sbale, bllamiiuHU.

16 fi

8W. i NK. I.

BE.JNW.l.

Roar not posed.

S 4

'

J7

Bl

Buraoa beds.

SK.lSW.i.

.. a

SW.iSW.i.

CflaL.gooil

SbBle, mira.

a FornctlOD tram uppfrmoat member ne Bull. U.S. Oeol. Sorvev No. 341, p.2S ("Crealon, BUtbcrf; CoUbukSi; NE. t NW.1mc.3,T. 18N., R. S2 W.'<)

206 Contbibutioms To Economic Geology, 1908, Past Ii.

BURNED COAL BEDS. tliickiiess iiniichimicler of iniuiyof the con 1 beds are obscured by burning' along tiio oiiferop. Tlic burning is of relatively small extent in tlie Jlesaverde, but murh more prevalent in the "Laramie" "Upper Liirnmie" coiil beds. The most prominent effect is the producliun in many of bright-red outcrops, tlie color being due to the ahiTadoii of the iron in the rocks adjacent lo the Inirned bed. Whether or not the neighboring rocks are reddened tliey are as a rule more or less sintered, the distance to which coloration and sin-

Eastebn Little Snake Biveb Coal Field, Wyoming. 207

tering extend varying from almost nothing to several feet from the actual seat of burning. A quarter of a mile southeast of Muddy Bridge a small caved drift in the Laramie'* formation exposes about 18 inches of bituminous shale underlain. by a few feet of dirty coal. Near by the bituminous shale has been burned, causing baking, reddening, and slumping of the overlying shaly sandstone, but the dirty coal composing the lower part of the bed is apparently not affected. In this connection attention should be called to the fact that sample 5299 in the table on page 206 was taken from a 2-foot bed separated by 3 feet of shale from 15 feet of burned coal. The physical appearance of the bed sampled was not altered by the burning, but the chemical analysis shows decided differences between this sample and the others collected from the same zone — notably increased fuel value, lower air-drying loss, lower volatile matter and higher fixed carbon giving higher fuel ratio, and, in the ultimate analysis, lower hydrogen and oxygen and higher carbon. Thus the coal in close proximity to a burned bed has by alteration become of considerably higher grade than its unaffected neighbors.

Coking.

So far as known the only coking test made on coals in this field was made on the Mesaverde coal at the Stemp Springs property in August, 1907. The chemical composition and physical characteristics show this to be among the very best coals in the region. The coking test was made in a regulation beehive oven 12 feet in diameter and 6 feet high in the arch. The floor was 2 feet tliick, with air spaces. Reports of the test state that the fire burned on top and refused to go down, this condition being attributed to inexperienced firing and to the cooling action of the air spaces in the floor. The result was ash on top, unbumed coal at the bottom, and some coke in the middle. This coke is stated to have analyzed 87 per cent of fixed carbon, 9 per cent of ash, and 4 per cent of moisture. In contemplation of a test in the near future the oven has been remodeled, with a 3-foot floor without air spaces, and the materials have been laid down for the construction of two new ovens. No report was made on the crushing strength of the coke obtained in the test, nor on the ratio of coal to coke produced.

DEVELOPMENT. HISTORY AND PRESENT OPERATIONS.a

Early openings. — Doubtless the first coal opening in the Little Snake River field was made in 1863 by the Overland Stage Company a short distance east of Sulphur. The coal from this opening was used for blacksmithing and heating at the Sulpluir stage station,

a For many of the statements regarding the history and of the field the writers ore indebted to Mr. U. F. Angier, Mr. M. W. DiUon, and Mr. John C. Friend.

208 Contributions To Economic Geology, 1908, Part Ii.

and small quantities are said to have been shipped for blacksmithing purposes as far east as Denver and as far west as Fort Bridger. After the completion of the Union Pacific Railroad an opening is said to have been made by the United States Government just west of Muddy Creek about 3 miles south of Muddy Bridge, the coal being used in connection with stations on the stage road that ran from Rawlins to the White River Indian Agency, Colo. The first opening made by individual enterprise is reported to have been the Easom mine (NE. J NE. J sec. 8, T. 12 N., R. 89 W. ; No. 17), situated between the present locations of the Company bank and the Darling mine. It was opened in 1876 or 1877, but the land was never patented and work was abandoned in the late nineties.

Carbondale mine. — The earUest opening that is still in operation seems to be the Carbondale mine, in the SE. J SW. J sec. 7, T. 13 N., R. 87 W. (No. 1). Coal was discovered at the present site of the mine in the early eighties by Frank Femald and Joe Hartenberg, and the mine was opened by George Doane to supply coal for mining operations in the Sierra Madre. Unsuccessful efforts were made to find coal nearer to the point of consumption. In the summer of 1908 the property was producing about 10 tons a day, employing seven men, using drilling machines, and shooting from the soUd. The maximum extent of the workings from* the outcrop at that time was about 1,300 feet, but the actual depth below the surface is slight throughout. The greater part of the original workings was abandoned in 1904, owing to difficulty with water and to irregularities in the coal bed caused by minor faults, and a new drift was started in March, 1908. The rooms are 12 by 20 feet, with stulls from to feet apart. The property is now owned by the United Smelters, Railway and Copper Company.

Stemp Springs mines, — The Stemp Springs mine (NE. i SW. J sec. 13, T. 13 N., R. 88 W.; No. 2) is owned by the Stemp Springs Coal and Power Company, the product being used in mining and smelting operations in the mountains to the east. The main entry is carried 6 feet high in the clear in coal, the rooms and pillars are irregular in size and shape, and stulls are set in the rooms from 3 to 6 feet apart. The main entry is driven just off the dip, which is about 2° and somewhat irregular.

Lucksinger opening. — The Lucksinger opening (SE. NE. sec. 18, T. 12 N., R. 88 W., Colorado; No. 4) has been operated for a number of winters by different persons, supplying coal for domestic use to the ranchmen of the upper Little Snake River valley. The coal has been mined from two large, somewhat irregular, more or less parallel drifts, no rooms being turned and very little timber being used.

a Numbers refer to locations on Plate Xin.

Eastern Little Snake River Coal Field, Wyoming. 209

Company hank. — The Company bank (SW. NW. sec. 9, T. 12 N., R. 89 W.; No. 5) fonnerly known as the Martin mine, is owned by the Snake River Coal Company. It was first discovered and opened about 1886 or 1887 by Noah Reader and has since produced about 10,000 tons, the present annual production being about 800 tons. The original entry runs as near the strike of the beds as the escarpment in which the coal bed outcrops will permit. Later entries run in directions successively approaching the north, the earlier entries being allowed to cave as the coal in their vicinity is worked out. The depth along the entries is a Uttle more than 400 feet.

Darling mine, — The Darling mine (SW. SE. J sec. 5, T. 12 N., R. 89 W.; No. 6), now owned by William Darling, was discovered and opened by Robert Turner and Ira Whiteaker in 1891 and later worked by Robert Mcintosh. It has produced about 10,000 tons and is now producing about 800 tons annually. It is developed by an entry running for 265 feet nearly on the strike of the bed, which dips about 8°. From the main entry minor entries are run off to distances of 150 feet or so, and rooms of irregular size are turned from these entries.

Angier mine. — The Angier mine (SE. J SE. J sec. 6, T. 12 N., R. 89 W.; No. 7), on the opposite side of Savery Creek from the Darling property, was discovered and opened by Joseph Wilson in 1890 and is now owned by H. F. Angier. Its total production has been between 10,000 and 12,000 tons; its present annual production is from 800 to 900 tons. The original workings consist of a drift run 400 feet N. 45° W., from which at a depth of 145 feet a second entry runs 700 feet N. 53° W., the coal being worked out in rooms extending between these two entries. These workings are now abandoned, but a somewhat similar system of mining is being followed in the new opening about 100 feet south of the old one.

DiUanmine. — The Dillon mine, opened in 1886 but now abandoned, lies outside of the area especially considered in this paper, in the NE. J NW. J sec. 36, T. 21 N., R. 88 but was for a number of years one of the principal producers in the vicinity of the Little Snake River field, the coal being used in the neighboring town of Rawlins. Two main entries were driven, the earlier one being abandoned, partly because of the quantity of gas encountered. Drifts from the main entries were run at various angles, work being carried to a distance from the outcrop of over 500 feet. The mine was originally owned by M. W. Dillon, who states that it was abandoned in 1900 or 1901 by the people to whom he sold it because minor faults were encountered. The character of the faults may be judged from the following extract from a letter by Mr. Dillon: 'The first fault is a downtlirow of 4 feet,

a Ball, Max W., The western part of the Little Snake River coal field, Wyoming: Bull. U. S. CJeoI. Survey No. 341, 1009, Plate XIII.

7963*— Bull. 381— KJ 14

210 Contbibutions To Economic Qeolooy, 1908, Pabt H.

about 200 feet from the portal ; the next is an upthrow of 4 feet, 240 feet from the portal; the next a downthrow of 6 feet, 450 feet from the portal."

Nebraska mine. — The Nebraska mine (NE. SW. J sec. 6, T. 20 N., R. 88 Ues just outside of the Little Snake River field, in the part of the Great Divide Basin field covered by Ball in 1907. It is the only mine in or adjacent to the Little Snake River field which is in the ''Laramie" formation, all the properties described above being in the Mesaverde. Mining is carried on throughout the winter months, the product being used in Rawlins, 7 miles distant. The dip of the bed varies from 12° to 20°. The coal is mined through a main entry, extending approximately down the dip, with entries turned at right angles from 100 to 200 feet apart.

Other openings, — In addition to the mines described above, there are in various parts of the field other openings, some of them supplying coal to one or two ranches in their immediate neighborhoods, others at present entirely abandoned or the scene of desultory prospecting. The Robertson mine (SE. sec. 4, T. 17 N., R. 90 W.; No. 16), in the Mesaverde, just east of Sulphur, has been worked to a depth of about 100 feet, 50 feet of which is a drift and the remaining 50 feet an irregular chamber. The Linde opening (SE. J SW. J sec. 8, T. 12 N., R. 88 W.; No. 3), also in the Mesaverde, has been worked to a depth of about 40 feet by a single straight, well-timbered drift. The Muddy Bridge openmg (NW. SW. J sec. 12, T. 15 N., R. 92 W.; No. 14), in the ''Upper Laramie,'' is an irregular, practically untimbered opening about 40 feet deep, sloping about 25°. The Corlett openmg (SE. J SE. sec. 4, T. 16 N., R. 92 W.; No. 15), also m the "Upper Laramie,'' has been carried about 40 feet down a slope of 35°. A few miles northeast of Baggs, in Coal and Cutoff gulches, are a number of openings in the 'Upper Laramie" (Nos. 9, 10, 11, and 12), of various depths up to 150 feet or more, none of which are operated at present. No. 10 is an excellently timbered slope dipping 25°, at present nearly full of water. No. 9 is also well timbered and nearly horizontal, but the coal is powdery. No. 11 is a drift approximately 150 feet deep, with coal as roof and no timbering. No. 12 is an irregular opening partly caved. The prospect opposite the Deary ranch (SAV. NE. sec. 15, T. 12 N., R. 90 W.; No. 8) is in the 'Laramie." It is an irregular slope about 30 feet deep, a small amount of timbering.

Future Development.

The rapidity with which tliis field will be developed depends almost entirely on four factors — market, transportation facilities, timber and water supply.

a liall, Max W., Tho w'estom part of the Little Snake Uiver coal field, Wyoming: Bull. U. S. Oeol. Survey No. 341, 1909, Plate XIII.

It

" CoE griff mi"''

Eo 21 2S Z3 24

Eastebn Uttle Snake Biveb Coal Fibld, Wyoming. 211

Market.

The field is unfortunate in being surrounded by producing areas which are more accessible and in having its most available coals farthest from the railroads and from any present market. To the west are the Rock Springs and Uinta County fields, to the east is the Hanna field, and to the south are the Yampa and Grand Hogback fields of Colorado. On the other hand, the demand from the country to the west is so great that the Union Pacific Coal Company has in the last few years ceased shipping its Wyoming coal east, leaving unsuppUed a vigorous demand in Omaha and adjacent towns. Denver, although in the vicinity of large coal fields, is a ready market for coal of this grade, and Salt Lake City is using all the coal mined commercially at Rock Springs and most of that in Uinta Coimty, with no apparent danger of overstocking. On the whole, the demand for coal is greater than the supply, and the rapid development of the West is increasing the demand constantly.

The natural local market for the coal of the southern part of the field is in the mining districts in the mountains along the eastern border of the coal-bearing area. On both sides of the crest of the Sierra Madre, just east of the Carbondale and Stemp Springs mines, is the Encampment copper district, to which the coal from those properties is now being hauled. Further development of that district or of any of the prospective mining camps on the headwaters of Little Snake River would call for further development of the coal field. The great need of the smelters in the Encampment vicinity is for coke, and this the coals of the Little Snake River field have not yet been able to supply commercially, but they can supply an excellent steaming coal for power and mining operations.

Transpoktation.

The field has at present no railroad, consequently no coal is produced within the field for consumption outside of it except that hauled by wagon from the Carbondale and Stemp Springs properties to the adjacent mining camps. The nearest railroad is the Union Pacific, about 12 miles to the north of the area especially treated in this paper and some 50 miles from the region of greatest present development. Approximately 50 miles southeast of the area is Steamboat Springs, Colo., the present terminus of the Denver, Northwestern and Pacific Railway, more commonly spoken of as the "Moffat road." It is planned to push this road westward through the Yampa field to Craig, Colo., within 37 miles of Baggs.

The Union Pacific Railroad Company is contemplating a branch from the main line southward to Craig. The starting point of the branch is still uncertain. It may be Rawlins, Creston, or WtwkwV

212 Contributions To Economic Geology, 1908, Part H.

ter. In any case the road will traverse this field from north to south. A line connecting the field with the 'Moffat road'' at Steamboat Springs is also discussed, to run tlirough the Hahns Peak region and traverse the upper Little Snake River valley. Still another line which may be constructed is the rumored branch of the Laramie, Hahns Peak and Pacific Railway from Halms Peak, the road being now under construction some 30 miles west of Laramie.

If a railroad is constructed through the field it will be comparatively easy to reach the coals by spurs. TTie flat-lying coal beds along Little Snake River from the mouth of Savery Creek upstream would be on any line traversing the valley, and a line from Baggs or Dixon would have a water-level grade. Construction of spurs to some of the coals lying in the higher Mesaverde ridges and plateaus might involve moderate engineering difficulties, but most of them could be developed by tracks laid in the dissecting canyons. No difficulty should be experienced in tapping the coals of the ''Laramie'' and Upper Laramie" formations even in the higher parts of the hogback region.

Timber Supply.

The fact that most of the coal beds of the field lie under shale roof makes the quality and price of timber an important item in any estimate of mining costs. The cost of timber at the Carbondale mine in the summer of 1908 is reported as about 15 cents to the ton of coal mined. The greater part of the field in Wyoming is devoid of timber, except for a few scattering scrub cedars in the Mesaverde ridges and a few cottonwoods along the river. East of Savery Creek, however, mucli of the country is well timbered. The Hayden National Forest includes Battle Mountain and extends northward and eastward across the Sierra Madre. The timber in most of the forest is estimated by the Forest Service at less than 2,000 board feet to the acre, although part of it is estimated to carry between 2,000 and 5,000 board feet.

The part of the field in Colorado lies almost entirely within the Routt National Forest and is most of it heavily forested. The timber available in the southeastern part of the field is thus capable of supplying the needs of very extensive mining operations.

Water Supply.

In general, those streams which liead in the formations younger than the Mesaverde are intermittent, and those whicli head in the Mesaverde or older formations are permanent either tliroughout their courses or wliile crossing and for some distance after leaving the older formations. Thus Savery and Battle creeks and their tributaries are permanent streams throughout; Muddy, Cow, Wild Cow,

aRiArra Madre folio, Atlas Nat. Forests U. S., U. S. Forest Service.

Easxebn Little Snake River Coal Field, Wyoming. 213

and Cherokee creeks become mtennittent some distance after leaving the Mesaverde; and Dry Cow, Red, and Cottonwood creeks are intennittent throughout. The one younger formation which is strongly water bearing is the Bishop ( ?) conglomerate, which furnishes mudi of the water in Savery and Battle creeks and in the headwaters of Muddy Creek. Springs along the base of this formation and in the limestone, where limestone makes up the overlying beds, are rather numerous for the semiarid rons, and the quality of the water is excellent. Another stratigraphic location which shows a tendency to develop springs is the boimdary between the Mesaverde formation and the Lewis shale. The springs at this horizon, however, are as a rule rather small and many are higlily mmeralized, particularly the sulphur springs in the vicinity of Sulphur. In the streams the alkalinity decreases and the quality of the water correspondingly improves as the flow becomes permanent. The water of Little Snake River itself is normaUy clear and of good quaUty. The waters of lower Muddy Creek and the lower courses of its tributaries are unfit for either human or boiler use.

So far as was ascertained the only wells in the field are sunk in the alluvium of the stream valleys. The water in these is of uncertain quaUty. Thus a well 20 feet deep at Muddy Bridge yields good water, but wells from 10 to 40 feet deep at Baggs and Dixon have developed water more alkaline than that in the river. It should be possible to supply small temporary operations by sinking shallow wells in the aUuvium of almost any of the main stream valleys, even where the stream itself is intermittent. For deep wells the Mesaverde is the most promising formation in the coal-bearing area. Wells drilled into the westward-dipping part of this formation should yield an abundance of good water. The supply of water to be obtained from wells in the "Laramie" and Upper Laramie" formations can best be judged by the wells of the Union Pacific Railroad north of the field. At a number of places between Rawlins and Tipton water was obtained at depths of about 500 feet in the Laramie" and overlying formations, but it was too alkaline to be serviceable. At depths of 1,400 to 1,600 feet alkaline water usable for boiler and domestic purposes is obtained in the "Upper Laramie." In this field wells of that depth in the "Laramie" and "Upper Laramie should yield a plentiful supply of water of about the same grade as that obtained at Riner and Wamsutter. The basal member of the "Upper Laramie" should be the best water-bearing zone of the two formations. The twp locations most favorable to the development of artesian water are in the Lewis shale valley at or near the Mesaverde boundary and in the valley formed in places by the middle or clay shale member of the "Upper Laramie," near the top of the lowest member. The two formations to be avoided are the shale immediately east of the Mesaverde and the Lewis shale except near the Mesaverde.

THE SOUTHERN PART OF THE ROCK SPRINGS COAL HELD, SWEETWATER COUNH, WYOMING.

By Alfred R. Schultz.

Introduction.

This report is a brief discussion of the economic geology of the southern part of the Rock Springs coal field, Wyoming. The survey on which the report is based was made during the summer of 1908 by John L. Rich, B. L. Johnson, Greorge E. Burton, and the writer. A detailed report on the coal of the Rock Springs field will be prepared as soon as time and the work in hand will permit.

The primary object of the investigation was the classification of the public land with respect to its coal content. Economic considerations therefore demanded that the work be based primarily on Land Office subdivisions, and that all coal outcrops, prospects, and geologic data be located with respect to established government corners. In the summer of 1907 similar work was done in the northern part of tlie Rock Springs field, ° and in a part of the Great Divide Basin coal field, extending northwestward from the Rawlins dome.* The work of the past season was a continuation of that of the preceding year. The mapping of the Rock Springs coal field was completed by the writer, while E. E. Smith completed the mapping of the Great Divide Basin field and closed the gap between the areas mapped in 1907.

The Rock Springs coal field is located in the central part of Sweetwater County, Wyo., on the east side of Green River, in the southern part of the State, the south end of the field being only a few miles north of the Wyoming-Colorado state line. (See PI. XIV.) It lies in the midst of the great Wyoming desert and occupies the crest of a low structural dome. This eroded dome, with its surrounding rim of Tertiary beds, gives to the field a natural boundary with reference to the outcrop of the coal-bearing rocks. The productive formations, however, underlie much of the surrounding country in the Green

aSchuIli, A. R., Bull. U. S. Geol. SuTA-cy No. 341, 1909, pp. 256-282. & Smith, E. E., BuU. U. S. Ciis>\. Sun-ey No. 311, 1909, pp. 230-242.

Southern Rock Springs Coal, Field, Wyoming. 215

River Basin, which includes within its borders the most important coaJ fields along the Union Pacific Raikoad between the Wasatch and Wyoming mountains on the west and the Rocky Mountains on the east.

The Union Pacific is the only railroad crossing this area and nearly all points in the Rock Springs field are readily accessible from the main Une. Several projected lines have been surveyed across the north end of the field, but no other line has yet begun active construction. The location of the Union Pacific Railroad places it in a position to control the future development of the field. The grade along its Une is moderate, and by short spurs with Ught grades, similar to those of the Superior and Gunn branches, it will be comparatively easy to reach all points at which mines may be opened to advantage. For all of the southern half of the field the most accessible routes lie along the main tributaries of Bitter Creek — Little Bitter, Killpecker, Salt Wells creeks and their tributaries. Spurs built up any of these valleys would be natural feeders to the trunk line along Bitter Creek.

The southern part of the Rock Springs field is covered by the public-land surveys. Because of an assumed poor survey a considerable tract, approximately 12 townships, was resurveyed by the General Land Office in 1906, and 24 townships were resurveyed by that bureau in 1907. In the part of the field south of the fourth standard parallel few comers could be found, and these do not agree among themselves; hence it is probable that they have not been authoritatively estabUshed. In this area it was found necessary to resurvey the townships before the land could be classified. During the summer of 1908 Tps. 15 and 16 N., R. 102 W., were resurveyed by the General Land Office and a detailed topographic map, with a contour interval of 50 feet, was made. The geologic work in these two townships was done by George E. Burton.

Glenn Smith, topographer of the United States Geological Survey, mapped in the summer of 1908 a 15-minute quadrangle in the vicinity of Rock Springs. The mapping of this quadrangle was done on the scale of 1 inch to the mile, the contour interval being 50 feet. Later in the season photographic copies of this base were used in mapping the geology and coal outcrops.

Of the territory outside of the areas of detailed mapping mentioned above, or approximately 10 townships, no maps other than township plats were available for field use. It was therefore necessary td make a topographic map as the geologic work progressed. In such territory all locations were made either (1) by pacing section lines or by making traverse from land comers found by such pacing, or (2) by plane-table station work, supplemented by plane-table traverse, triangulation, and intersection work, checked and tied to laid coTCiKt:*

216 Contributions To Economic Geology, 1908, Paet H.

In areas where no comers could be found plane-table control was used entirely, road and line stadia traverses being made wherever necessary.

Altitudes were carried by stadia, altimeter, Locke level, and aneroid, all being adjusted to the temporary and permanent bench marks along the line of levels run around the dome from Rock Springs north to Steamboat Mountain, thence south to Point of Rocks, Black Buttes, and around the south end of the dome back to Rock Springs. Lines were run one-fourth to one-half mile apart, and the outcrops of aU the more important coal beds were traversed and the traverses tied to land comers. The field sheets were made on the scale of 2 inches to the mile, with a contour interval of 50 feet, and will be used in the preparation of the maps to accompany the final report. The maps (Pis. XIV and XV) accom- 'panying the present report have been prepared from the field sheets, and although approximately correct they may differ in minor particulars from the final large-scale maps.

Topographic Features.

The Rock Springs coal field Ues along the eastern margin of the Green River Basin and includes on the northeast a part of the Great Divide Basin. It occupies the major part of the Rock Springs structural dome, which is completely surrounded by Tertiary beds. Witliin this field there are five distinct topographic districts, each presenting entirely different characteristics from those of its neighbor. Only the most prominent peaks and ridges that encircle the dome rise above the adjacent Tertiary escarpments. The divide between the Green River and Great Divide basins has no topographic identity or distinctness. It lies for the most part several miles east of the dome and is formed in some places of Tertiary rock, in others of Cretaceous rock, and in still others of igneous rock. The divide is irregular, extending across several distinct topographic districts.

The princi{)al topographic features of this field are due to (1) hard, resistant sandstone beds of the Mesaverde formation; (2) hard, resistant limestone and sandstone beds of the nearly horizontal Green River ami Wasatch formations; (3) migrating sand; (4) soft beds of the Wasatch formation, Lewis shale, and shale underlying the Mesaverde in the central part of the dome; (5) gravel slopes of the Bishop conglomerate; and (0) igneous rock.

The hard, resistant sandstone of the Mesaverde makes notable concentric ridges or hills that are more or less continuous about the central portion of the dome. These ridges contain the most important coal beds of the field and are in general separated from one another and from areas of equally or more elevated younger rocks

Southern Bock Springs Coal Field, Wyoming. 217

by belts of low relief. Two pronounced depressions are carved in the soft shale overlying and underlying the sandstone of the Mesaverde formation. These low valleys are natural routes of travel and afford easy access fiom the railroad to the more rugged ridges containing the coal. The shale below the Mesaverde gives rise to low rdief in the central part of the Rock Springs dome and is the cause for the development of Baxter Basin.

The hard, resistant limestone and sandstone beds of the Green River and Wasatch formations produce notable table-like forms bounded by prominent escarpments of considerable length. In places the harder layers in these beds produce bench after bench in regular succession separated by nearly parallel valleys. In many places the more prominent ridges form bluffs and in parts of the field the beds present characteristic badland topography.

Huge dunes formed by migrating sand constitute the most conspicuous topographic feature in the northern part of the field.

The soft beds of the Wasatch form low depressions along the synclinal trough of the Great Divide Basin and along Elillpecker Valley. This formation contains numerous beds of coal, few of which are well exposed, so that their presence over much of the region can only be inferred from a study of sections where it is better exposed. The topographic features in this area are such that the coal beds are readily accessible.

The long, gentle, grass-covered slopes of the hills capped by the Bishop conglomerate form a striking topographic feature and outline in a general way the peneplain that was formed immediately preceding the epoch marked by the deposition of this material.

The igneous rocks in this field rise like landmarks out of the arid plateaus of the Red Desert. The lava forming these rocks flowed from a little group of volcanoes far removed from the centers of igneous activity and spread out on a nearly horizontal surface. The evidence at hand seems to indicate that the surface upon which these lavas flowed is the same as the peneplain referred to above in connection with the Bishop conglomerate. Their nearly concentric cones, needle-like necks, irregular dikes, and table-like sheets afl'ord a striking contrast to the topographic features of the surrounding hills.

The drainage of this area for the most part flows to the Pacific. The main streams are not affected by the Rock Springs dome, which in a way connects the Uinta and Wind River mountain ranges. The most prominent stream in this field is Bitter Creek, which controls the major part of the drainage of the dome. It flows across the central portion of the dome at nearly right angles to the major axis and has carved a broad valley along which the Union Pacific Railroad 18 constructed. The three largest tributaries of Bitter Cvek —

218 Contributions To Economic Geology, 1908, Pabt 11.

Eallpecker, Little Bitter, and Salt Wells creeks — have been shaped indirectly by the fold. On account of the difference in the hardness of the beds these valleys extend in the main along the strike of the beds and are approximately at right angles to Bitter Creek. In some places, as in the valleys of Salt Wells and Black Buttes creeks, the small streams cut across several of the ridges before joining the main stream, and one of the tributaries of Salt Wells Creek cuts three times across a pronounced hogback ridge 1 ,000 feet in height instead of following the softer shale along the strike of the beds.

At the south end of the dome the streams do not cut directly across the major axis. Red Creek, on the west side, drains southward into Green River after cutting a channel through part of the Uinta uplift. On the east side of the axis Vermilion Creek drains southeastward, paralleling the Uinta uplift through the upper half of its course, and finally cuts directly across part of this uplift and unites with Green River near the south end of Browns Park.

All the streams on the west side of the dome between Red Creek and Jack Morrow Creek not included in the Bitter Creek drainage basin are more or less nearly at right angles to the major axis.

Geology.

Structure. General Statement.

The structure of the Rock Springs field is comparatively simple. It consists of a huge dome of Cretaceous and Tertiary rocks which rise in the midst of the nearly horizontal rocks of the Green River basin and partly divide the southern portion into two smaller basins, the Bridger Basin on the west and the Red Desert or Washakie Basin on the east. The major north-south axis of the dome is approximately 90 miles long and is located close to the west limb of the anticline. The beds along this limb dip from 5° to 30 W. ; those along the east limb dip from 5° to 10° E. The minor east-west axis is approximately 50 miles long, extending across the dome in a direction north of east and south of west, passing north of Aspen Mountain and through a point 4 miles north of Black Buttes, a station on the Union Pacific Railroad. Several small anticlines and synclines are developed upon the main dome, but for the most part they are unimportant. Two of the largest of these cross folds occur near the south end of the dome and are parallel to the minor axis and to the trend of the Uinta uplift. The oldest beds involved in this structure are exposed in the vicinity of Baxter, a station on the Union Pacific Railroad, and outcrop for a distance of about 30 miles along the crest of the dome.

Four coal groups are exposed in this area, and it is believed that another group) is concealed by overlap of the youngest or strati-

graphically highest coal group. Three of the four groups are more or less continuously exposed and lie somewhat concentrically around the non coal-bearing central part of the dome ; the other is exposed only in the northern two-thirds of the east side of the dome. The structural relations of the two lower coal groups (Rock Springs and Almond) are those of two formations that are conformable and outcrop in concentric belts around the central portion of the dome. These two coal groups are separated from each other by white sandstone about 800 feet thick, well exposed at Point of Rocks.

The third or Black Buttes coal group rests conformably on the underlying formation and outcrops in a zone extending along the east side of the dome from T. 23 N., R. 103 W., southward to T. 17 N., R. 101 W. This zone is thought to be concentric with the outcrops of the imderlying formations. Although no exposures of it have been seen on the west side of the dome, its beds are believed to be covered there by the Black Rock coal group, which rests in some places upon the beds of the second or Almond coal group and in others upon the white sandstone between the Rock Springs and Almond coal groups, and which in one place (T. 18 N., R. 105 W.) comes into contact with the Rock Springs coal group as a result of faulting. Along the east side of the dome the Black Buttes zone is separated from the Almond zone by a belt of non coal-bearing Lewis shale, which doubtless continues around the dome in the same way as the Black Buttes and Almond coal groups and underlying formations.

The Knobs-Cherokee coal group is not exposed in the Rock Springs dome, but is believed to be present between the Black Buttes and the Black Rock coal groups, probably extending around the dome in a belt that is somewhat concentric with those of the other groups.

The Black Rock coal group lies unconformably upon the Black Buttes and older coal groups and like them outcrops around the dome more or less concentrically with the others. In places this group conceals wholly or in part the underlying group. By far the most pronounced unconformity observed in the field occurs at its base. The Black Rock coal group occupies a large area in the northeastern part of the Rock Springs field and in the Great Divide Basin. The same group contains coal beds in the low synclinal trough between the Rock Springs dome and the Rawlins anticline.

Faults.

The general dome or anticlinal structure is somewhat complicated by many normal faults of considerable throw. Here and there the horizontal displacement amounts to 3 miles; the vertical movement is usually less than 100 feet, but in a few localities reaches several

a See Bull. U. S. Qeol. Survey No. 341, 1909, pp. 220-255.

220 Contbibutions To Economic Geology, 1908, Paet H.

hundred feet. Near the south end of the dome, in T. 14 N., R. 103 W.y along the crest and south limb of a low anticline parallel to the Uinta uplift, is an overthrust fault which has a vertical displacement of 200 feet. The fault plane dips to the south about 20 from the horizontal, indicating that the thrust came from that direction.

Some of the faults extend across the dome, others cut only one limb or part of one limb, and still others extend for only a few hundred feet or a mile or two and then die out. Some of the larger faults have been traced for a distance of more than 20 miles. The general trend of the faults is nearly at right angles to the strike of the rocks or across the axis of the major anticline. In some places, however, the angle of departure is laie and the fault parallels the strike more nearly than the dip of the beds. This is well illustrated near the north end of the dome, where the faults cut some of the rocks at right angles to their strike and before dying out continue approximately along the strike of the underlying beds. The position of the larger faults is shown on Plates XIV and XV. In addition to the larger faults readily detected on the surface, numerous small faults are encountered in mine workings. In the Rock Springs coal group, from the Van Dyke coal bed upward, there is at many places a system of characteristic joints or slips that cut the coal at short intervals from floor to roof. These slips incline toward the south, and along many of them there is displacement of one-half inch to a foot or more. As a rule these small faults do not interfere with mining, but rather assist in breaking or parting the coal, thereby making it easier to mine. The larger faults, however, greatly increase the difficulties of mining and tend to retard development work. In regions of much faulting the offsetting of the coal beds may so increase the cost that mining will be abandoned or development work stopped. The exact date of the faulting is not known. It may have occurred at various times during the gradual uplift of the dome after the close of the epoch of Cretaceous deposition. It is believed, however, that most if not all of the faulting is associated with the movements that gave rise to the leucite lava flows and renewed uplift in the Uinta Mountains immediately before the period of deposition of the gravel, which is entirely independent of the faults and folds in the underlying rocks.

Stratigraphy. Outline Of Geologic History.

The beds of coal in the Rock Springs field and the rocks in which they occur form only a small part of the great sedimentary series that was deposited at a time when this part of the continent was largely submerged. Tlie beds were deposited in a nearly horizontal position during the various stages of submergence and emergence under con-

Southebn Bock Springs Coal Field, Wyoming. 221

ditions ranging from those of a deep sea to those of shallow water or swamps, in waters that were salt, brackish, or fresh. The oldest rocks exposed in the Rock Springs dome are of Montana age. From the epoch of their deposition until the end of the Cretaceous no profound disturbance or broad orographic movements occurred in this region. There was a gradual change from deep-sea to shallow-water conditions, with oscillations back and forth, giving rise to swampy areas that were favorable for the accumulation of coal beds. From the marine stages of the lower Montana there is a regular succession upward through the brackish-water to the fresh-water stage. The strata, so far as can be seen, are entirely conformable and the series is complete. In late Cretaceous time the horizontal beds deposited in this region became involved in a movement which gave rise to the low anticlinal arch that subsequently developed into the Rock Springs dome. This period of gentle doming or warping was accompanied and succeeded by one of deposition in shallow fresh water, during which a series of beds, conglomeratic at the base and coal bearing throughout, were laid down upon the older marine and brackishwater beds and, in places along the margin of the rising dome, upon the eroded edges of the older rock. In succeeding epochs fresh-water beds in which no coal occurs were deposited to a large degree in lake basins.

After the deposition of the fresh-water beds movements of the earth's crust folded and broke the originally continuous Cretaceous and later sediments, so that it is necessary to study their attitude of superposition in order to determine the relation of the beds to one another. There are also evidences that during great time intervals deposits were not formed or that if laid down they were subsequently removed, leaving little or no record of their existence. Particularly is this true of post-Cretaceous time. After the fresh-water beds had been laid down there was a long epoch of erosion in which the entire region was reduced to a peneplain or nearly level surface. This was succeeded by mild volcanic activity, during which the leucite lava flows north and west of Rock Springs were poured out on a planed off, nearly level surface, formed by the truncation of the underlying rocks. This volcanic activity culminated in or accompanied orographic movements that resulted in rapid erosion and the deposition of an extensive gravel sheet over the entire region from the Uinta Mountains northward to Bitter Creek. This gravel sheet is independent of the folds and faults in the underlying rocks, which are beveled across entirely irrespective of either hardness or structure. From this gravel-covered plain the present topographic features have been carved in late Quaternary time, almost solely by erosion.

222 Contbibutioks To Economic Oeolooy, 1906, Pabt Ii.

Description Of Formations.

Tho investigations of the Rock Springs field have shown that the subdivisions mapped by King and Powell can not be applied to the sequence of rocks in this region. A large collection of fossils obtained by members of this party and studied by F. H. Knowlton and T. W. Stanton indicates that the several formations have the geologic time values indicated in the accompanying table. In this table the general character and succession of the Cretaceous and Tertiary rocks, together with their economic importance, are set forth. As nearly all tho rocks exposed in the Rock Springs dome are closely related to tlio coal-bearing rocks, the entire stratigraphic section is here presented.

Geologic formations of the Rock Springe field.

Forinfttioii.

Ignfous.

Kconomlc (InilKnation.

Leucite lav A.

5?

OtO

I I liUhup

rnoonformlty

(travel.

Oto JOO

Oto

I'liconformltv

0 to

0 to

Description.

Dikes, flows, volcanic necks, and agglomerate.

Water worn and subangular pebbles and bowlders, many of them from 1 to 6 feet in diameter. -embedded in flner gravel and sand.

Massive, irregularly bedded sandstone; white, yellow, and brown shaly* sandstone: some limestone and interlHxided shale.

shale, sandstone, and limestones t.some of which are oolitic some dark-color* bituminous shale.

clay, shale, and sanvis'.or.e. in plactt? slichtiv VrvviiKvs highly t'Arprr.ent of iJanev Kim

Economic value.

Potash niter occurs in some of these rocks.

Good water horlion.

Supplies many of the springs in southern part of field.

Contains traces of oU in bituminoos shale. In places rock seems to have been bamed in cfxisequenoe of presence of oil.

80UIHEBN BOCK SPBINGS COAL FIELD, WYOMINO. Otoloffic/ormaticmt tifAe Rodk prinffi/drf— Continued.

Black

AltcmatlnK lay en m whi tr, yellow, and brown tart-

anrl carbuDBOTOUS itaain, with coal beds and conglomeraU contolnlnc ennfu andquariailcpeb'

*h[)e codcntlonarf sand-

Kgultir shapes. Basal iandllone la congloineratlc. Sandstone bardeni locally and wnCtaera Into tama rmmbUa; lanie 3o( or spberksl conorp- Uom. Largeoraaa-bedded leddkth xaiidslone IDnns badlaod (opoiraphy In Red valley and Fire Hole tiailQ.

Utrmadne layei-i ol

Foults abound la plain Eiposed only f- " narthtra put or I

a;

alialti, (ilKhly I eaodalonr and la bed] at white sa

upper portion ne iOrtakee and In tl lower portion ne Knobii. RFfardli cttcroltw and ovi

roBlble sour

Coal btarlig. Uan; coal .

Kock Snrlna and PdIoi ol ttocii.

CONTBIBUTIOHS TO ECONOMIC GEOLOGY, 1B08, PABT U. Geologic farmaHona of Ae Sodt Springi fidd~-ContimMd.

Rock SprlasE 001

iMve while mH yellow- Ish BiLDdBtone. ihlrdootiKlDinmlio, with

quarts ptbbla. Sancl-

Bscarpmrau and taofttrack rldsffi. giving rlsa to the 'while wuU°'

lo yellow sandstone.

tbiakness o( coaLTii till: KTOup BlxmC flO feet.

Black and drab sbales, t

Water bMulag.

Y zelda artnlaa water m partiDf Add. Klowfug weLli at Point al Rocki. Wells norlb- T Superior, lil iunfmd In

Water wlil pi

be encounG tbesebeds ba

Coal bcarlRg.

Uaay large coal bb

erbeds. Bat coal la the ItDck Sprlngi field. Impottatit mines al Rock Sprinis, Sweetwater, eialrlawn, Ounn. and Superior. Hanj

ail Rank

Arteslan- t Supcrtor

ably supply water outilde oitne Mgta and eacarpmeDtt mi rouDdlng Salter B*.

Pnalbleaoumorel

Coiuideratilr it i

Igneous Rocks.

In the nortli half of the dome numerous intrusive and extrusive masses have been forced up through the Cretaceous and Tertiary rocks and cap these rocks in several localities. The exposures of leucito range from talus-covered hills, isolated volcanic necks, and associated dikes to lava flows with cones, intruded sheets, and dikes. Many of the lava sheets present abrupt walls from 50 to 100 feet in height. Some of the lava flows and volcanic necks lie along fault lines through which the molten mass may have found an outlet. In other localities the lava seems to Jiave forced its way through the rocks without causing any disturbance. The sedimentary beds lie prac-

Southern Rock Springs Coal. Field, Wyoming. 225

tically horizontal around the igneous masses, which contain many fragmentary inclusions of the country rocks. Although the lavas have cut many coal beds and rocks of the coal-bearing formations, in no place were the coal and igneous rock seen in actual contact. Coal samples Nos. 5597 and 5599 were collected from two prospect pits in sec. 10, T. 21 N., R. 102 W., a few rods below the overlying lava sheets and about a mile from several volcanic cones, but showed no apparent difference in physical or chemical properties from coals lying at a distance from the igneous rock. The exact age of these leucite flows has not been definitely determined. They are positively later than the Green River formation and may be considerably later. From the best evidence at hand it is believed that a period of mild volcanic activity followed the peneplanation mentioned in the outline of the geologic history.

Ngn Coal-Bearing Rocks.

In the Rock Springs field there are several zones of non coal-bearing rocks below, between, and above the coal groups. Below the Mesaverde formation is an unnamed dark-gray to black shale of Montana age, which occupies the central part of the dome in Baxter Basin. This is the oldest rock exposed in the field. Above this shale and below the Rock Springs coal group occur sandy shale and sandstone, which form the lower beds of the Mesaverde formation. The upper of these beds gives rise to the main scarp surrounding Baxter Basin, often referred to as the golden wall.''

Between the Rock Springs and Almond coal groups is a massive white sandstone, well exposed at Point of Rocks, which contains here and there traces of bituminous matter and beds of coal from 2 to 18 inches thick. It is not, however, coal bearing in a commercial sense. The upper third is more compact and conglomeratic than the lower portion. This sandstone gives rise to the main scarp surrounding the Rock Springs coal zone, often referred to as the white wall." In parts of the field this escarpment is from 200 to 500 feet high.

Between the Almond and Black Buttes coal groups is a mass of soft gray and drab shales, highly gypsiferous, which on weathering give rise to regions of low relief that furnish excellent natural routes for travel across the field. No trace of coal has been found in these beds.

Overlying the Black Rock coal group are four groups of beds which are not known to be coal bearing in this region. The lower two belong to the Wasatch formation, and the upper two to the Green River formation. The beds immediately overlying the Black Rock cool group consist of fissile shale, conglomerate, ooUtic Umestone, shale, clay, and sandstone. Some of the greenish-white shale of these beds is very fissile and closely resembles the shale in the lower

Bull. U. S. Geol. Survey No. 341, iJWtt, p. 272. 7963*— Bun. 381—10 15

226 Contkibutions To Economic Geology, 1908, Part Ii.

part of the Green River formation. The second group of beds consists of red or varicolored conglomeratic sandstone, shale, and clay, which are well exposed in Laney Rim and Cathedral Bluffs, southwest of Wamsutter. The third group of beds belongs to the Green River formation and consists of white and green fissile shales, limestone, and sandstone similar to those so characteristic of the lower part of the Green River formation in other parts of the Green River Basin. At the south end of the dome, outside of the territory here described, traces of coal were found near the base of these beds, but throughout most of the field no coal was seen in them. The fourth group of beds also belongs to the Green River formation and consists of massive, irregularly bedded sandstone, sandy limestone, and shale that are well exposed north of Wilkins, a station on the Union Pacific Railroad, a few miles west of Rock Springs, and in the vicinity of the town of Green River. The same beds are present in small outliers on the east side of the dome in the vicinity of Pine Butte.

Overlying all these beds and obscuring many of them is a mantle of slightly indurated gravel (Bishop conglomerate) that extended originally over the entire region south of Rock Springs to the north flank of the Uinta Mountains. This material has been dissected by the streams until only remnants are left. The largest of these extends southward from Aspen Mountain to Miller Mountain (Tabor Plateau) and westward between the headwaters of Sage and Little Bitter creeks. Two other remnants of considerable size are found on Little Mountain (Quien Hornet of the Powell Survey) and on Pine Mountain (Bishop Mountain of the Powell Survey) . The first is separated from Miller Mountain by the valley of Sage Creek and the second lies about 10 miles southeast of Miller Mountain. At many other localities small areas are capped by similar sheets of gravel lying at accordant elevations, wliich once formed parts of the sheet that mantled this entire region.

In this report all the non coal-bearing rocks are considered collectively and mapped in two patterns irrespective of their stratigraphic relations. All the beds above the coal groups are shown in stipple; those below and between the coal groups are shown in a parallel ruled pattern.

Coal-Bearing Rocks. General Statement.

The oldest coal-bearing rocks exposed in this field are of Montana age. The Frontier formation " of tlie Colorado group, which contains the high-grade Kenimerer coals of Uinta County, although not outcropping in this area, is believed to be present and to contain workable beds of coal. It is also believed that along the axis of the

o Smith, E. E.. Bull. U. S. Geol. Sunny No. 341. 1909. p. 226. Schultz, A. R., Bull. U. S. Geol. Survey No. 316, 1907, pp. 212-241. Veatch, A. C, Bull. U. y. Geol. Survey No. 285, 1906, pp. 331-353.

Southern Rock Springs Coal Field, Wyoming. 227

dome in the vicinity of Baxter station these coals may lie near enough to the surface to be mined some day, but at present no borings have penetrated to a sufficient depth to reveal them, and the depth at which they may occur and even their existence are somewhat problematical.

The Mesaverde formation consists of four distinct members, two of which are coal bearing. The lowest member consists chiefly of sandstone, shaly sandstone, and shale, all of which are barren of coal and show no indications of carbonaceous matter. The two coal-bearing members of the Mesaverde are separated from each other by massive white sandstone 800 to 900 feet thick. The lower one of the Mesaverde is known as the Rock Springs coal group and the upper as the Almond coal group. The Almond coal group is overlain by the Lewis shale, and the remaining coal-bearing rocks exposed in the Rock Springs field are of post-Montana age. Above the Lewis shale, the upper formation of the Montana group, in the western part of the area are two groups of coal beds separated from each other by an unconformity of considerable magnitude. For convenience in the following discussion the lower has been called the Black Buttes coal group and the upper the Black Rock coal group. The unconformity between them may in places escape observation. The lower group of these post-Montana coal beds is of ''Laramie" age; the upper group belongs to the Wasatch formation, and is therefore of Tertiary age. In the region to the east there occurs still another coal group at the base of the Tertiary, called undifferentiated Tertiary by Smith in his report on the coal field of the Great Divide Basin. This group contains the coal beds at Knobs and Cherokee and in this paper it will be referred to as the Knobs- Cherokee coal group, or ''Upper Laramie" formation. According to the paleobotanical evidence it is of Fort Union age and is the same as the "Upper Laramie'' of central Carbon County, described by Veatch,* and the "Upper Laramie'' of the Little Snake River field, described by Ball on pages 186 to 213 of this bulletin. It is exposed on the west side of the Rawlins dome, but does not appear at the surface in the Rock Springs dome, the entire formation being concealed by overlap of the Black Rock coal group.

Rock Springs Coal Grox7P.

The Rock Springs coal group is the most important in this region and the one containing the highest-grade coal. Its lower portion consists of heavy beds of ridge-making, coal-bearing sandstone and the remainder of brown, yellow, and white sandstone, slialc, clay, and interbedded coal. It contains at least twelve coal beds ranging from 2 to 10 feet in thickness and many other beds less than 2 feet

aSmith, E. E., Bull. U. S. Geol. Survey No. 341, 1909, pp. 233,24. Vwtoh, A. C, Bull. U. S. QeoL Survey No. 316, 1907, pp. 244-2W.

228 CONTBIBUTIONS 10 ECONOMIC QEOLOaT, 190B, PAST H.

truck. The total aggregate of coal beds over 2 feet thick in the Rock Springs coal group in the vicinity of Superior is more than 80 feet, and in the vicinity of Rock Springs it is more than 90 feet. These beds occur somewhat irregularly throughout the group, but are fairly persistent along the strike. They have been prospected all the way from Aapen Mountain northward to Rock Springs and Superior and on the east side of the dome to Black Butte Mountain. South of Superior the coal beds are somewhat thinner and the number of beds is not so great as between Superior and Rock Springs, and therefore very little prospecting has been done in that area. South of a line drawn through the southwest corner of T. 16 N., R. 104 W., and the southeast corner of T. 18 N., R. 102 W., the group is not known to be coal bearing. In part of this area the exposures are poor. Some coal beds may be present, but none were seen. The rocks here appear to be a continuation of the beds that were laid down under conditiooa similar to those which existed during the deposition of the "golden wall" in the nortliern and southern parts of the field. The coal is, however, of high grade and additional mines are certain to be opened in the near future at other points along the outcrop from Rock Springs to Aspen Mountain. Mines are in operation on upper beds of this coal group at Sweetwater, liock Springs, and Superior. At Gunn and Van Dyke the coal beds near the bae of the group (the Van Dyke coal beds) are being mined. New mines were to be opened in 1908 along Killpecker Valley, nortli of Rock Springs, but owing to tlie money stringency work was greatly delayed and some of it temporarily abandoned,

Tlie area underlain by the Rock Springs coal group was mapped in detail and the locations of mines, prospect pits, and tlie coal outcrops were determined by a stadia survey. The locations of the outcrops of the more important coal beds as well as tlie formation contacts arc shown on Plate XV. The general character and thickness of the coal beds in the Kock Springs coal group are shown in the following sections taken at various points along the outorop:

f 0/ fi,al beds i

1 fhe aoulhem pari of the Eoek

I Section ol coal bril.

Shsle, broi

Coal

IT IDS Shale, broi

SE. ISW. i. 14 '

Shalf, brown B

beds In tbe aonbeni puc ol the Hock Springs Seld see BuJJ. U. S. Qeol.

Bodihebh Bock Spbinqs Coal Field, Wyoming.

Stetion* of eoal btdi tn the Roet Sprinfft eoal group in iht louUiem part of the Rocl

Springi field, Ifyoininj— Continued

Locatkn.

Sectional (Ml Iwd.

"

T,

R.

Quanm.

t.Ir.

eW. INW.l,

Bhale, brawn 1 SandslDne,

NW.iBW.l.

Ib

m

„

Coal fl

1 Shale.

1 fi

BW.JSW-i.

'

NW.lNE.i.'3*

U

Ids

'Si ,

Shale t

Coal 2 4

Done B

Sandstone.'""

8E. 1 Be. I.

'

,.

Cmj 7

Shale.

SW.iSE.l.

,.

,.

™

Ccai fi Si

Nk.1Ne.1.

Ib

1 Coal 1 S

Sw. 1 Se. (.

Ib

Coal 10

Ih

*10(

NW-iNE-l.

'

Ib

Iw

Coal 1

NW.l NE.i.

Ib

™

Coal e

BE.iaw.i.

,.

Ib

Iw

Coal a

Coal i

KW.lNW.i.

,.

Coli u

NE.iNW;i.

,.

Cosi J

Shale.

NW.iBW.l.

'

Im

Coal 3

cwi!!!!!!!! i a

2S

Ib

coti a 10

Shale 1 i

NB.iNW.l.

SW-iNW,i. B

Coal.. i 1

los

Clay. Coal B

Coal S

Coal 1 2

BW-lBE-i.

M

Im

Coal 10

BW.iSW.i.

BW.iBW.i

2D

lU

sSie.";::: a

Coal 3 fl

SE.JBE.i. BE.}flB.l. 30

Iw

Bandiione". S

Ih

Nw.18W.I.

M

Ib : Ids

Cooi 1 n

none 7

1

*w.isw.t.

at

. Shalf. Shale.

230 Contributions To Economic Geologt, 1908, Pabt H.

Almond Coal Group.

The Almond coal group is of second importance in the field. Its coals are not so good as those of the Rock Springs coal group and up to the present time have been little developed. The group consists of beds of carbonaceous shale, clay, and brown and gray sandstones, with numerous beds of coal in the lower half of the formation. Several coal beds from 2 to 8 feet thick have been prospected in various parts of the field. Unlike the Rock Springs coal group the Almond is known to be coal bearing around the entire dome. Mines were opened in these beds just east of Almond or Point of Rocks, in T. 20 N., R. 101 W., when the Union Pacific Railroad was first built. They were soon abandoned, however, and not reopened until the summer of 1907. The old No. 6 mine at Rock Springs (sec. 22, T. 19 N., R. 105 W.) was opened in these beds in 1882, operated for a short time, and abandoned in 1886, as the coal was found to be inferior to that obtained from the Rock Springs coal group. The aggregate of coal beds over 2 feet tliick in the Almond coal group is from 15 to 30 feet and the beds occur chiefly in the lower half of the formation. The total thickness of the Almond coal group is exposed only on the east side of the dome. Throughout the remainder of the region the upper part is concealed by the overlap of the Black Rock coal group, and on the southwest flank of the dome the whole of the Almond coal group is covered by overlap of these same beds. In t!ie area from T. 18 N., R. 105 W., to T. 14 N., 11. 104 W., no exposures of the Almond coal group were seen. It is present, however, beneath the Black Rock beds and is believed to be coal bearing. The following sections, which are a few of the numerous measurements made at various points along the outcrop, show the character and thickness of these beds:

Sections of coal beds in the Almond coal group in the southern part of the Rock Springs

fieid Wyoming

Location.

Qiiarltr. St'<'. T. K.

Soctloii of coal IkmI.

! Shalo. Ft. in.

SW.iSW. :. 14 Coal 7 11 .

Shalo. '

Shall'.

Coal W 4

Shah' 1

SW.iSW.i. ; (. i 14 , IdJ Coal 4

I Shale. - -

s 4

Shalo.

NE.iNK.'. N 14 102 Coal 7

Shale.

Ivocation.

r I " '

Quarter. Si-c. T. K.

i SNV. ;. i 10 14 102

NW.i XW.i. V.\ 14 10.1 I

Sivtion of coal led.

Shale.

Coal Shale.

Ft. in. ...3 t)

Shale. Coal Hone... Coal

... 1 6

... 2 6

a For .sections of tlirso ImmLs in Uie northern part of the Kot:k Springs held aca Bull. U. S. tieol. Survey No. 341, lyo't. i>. "Jt.

BOUTHEBN BOCK SPRINGS COAL FIELD, WtOMING.

Stetiolu ofeoal w the Almond mtil iriup in the southern part of Ae Rock Springt fitU, It yo 111 ip— Continued

Location.

Cloirt.r.

Bm.

T.

S.

Boo

T.

R.

Ne.Jnb.*.

"

Philo 1

sw.iaw.i.

„

cSr":-: ,

Shale, brown 1

"

lOJ

Shale. Coal 3

12 G

MK.iNB.l.

9E.iSE.i.

S

Cob] 4 10

8K.iSE.i.

Co.] J 10

"

„

n

aK.lSE-1-

s

. 4 10

SW.tMW.l-

NW.tSW.-l,

n

Nw.ja-w.i.

"

Con 3 10

NE-lBW-i.

Cold. S 1

.'

,.

Ss.- '

Be. Ink. 1-

NK.iaw.i.

a.iBW.t.

Bhnle S

BE.lMW.i.

™

Shale.

Shate.

M g

NE.iNW.l.

Shale. Coal 1

BT-IBW-l.

™

Bhiilr.bniwn S 8ha1p,bran i

i a

NW.iNW.J.

Id

loo

NW.lSW-i.

Is

ira

Cooi 4

30 fl

Ne.1Be.I.

Id

Ids

"Si

s t

MW.tNW.l.

2D

,.

7 B

aE.lNW.l.

,.

Ids

Shale, ttrab.

BE.lNW.i.

Shsle. hiDWD S tfflU 2

Cml ".'.

Coal.,..'.'. Shale, car

Nw.Ink.).

,.

'"

auto, blown 2

l!-T

Oontbibutions 10 Economic Oeologt, 190S, Pabi Ii.

Loomon.

fitaUouoI cool bed.

Loaillon.

Quutn.

.

T.

n.

R-

ME-iSE.}.

m

CDkl,boD;.. 5

iNW.iNE.J.

™

Shale and

iWne T 6

CmJ 1 e

Shale 3

Coal 2 6

Shals 1

SW.lKE.i.

Sandnone... 3 ShUa, brown U

Si'"" s .

Sbale,bravD. 3

NW.iSE.i-

ns

CmI i SB.iBK.l.

StBlo, brown. 2

Ids

Shale, brown 3

Shale, brown Z KhnlK.iirown

NW.lnK.i.

""'

,U5

Shalo.

Black Buttes Coal Group.

Along the east siile of the dome the Black Buttes coal group, s( as known, lies conformably upon the marine Lewis shale. The basal member of the group consists of a massive bed of yellowish-white sandstone, in places ovor 100 feet thick, and is not known to be coal bearing. This member, resting upon the soft, friable Lewis shale, forma steep lulls anil cliffs along the contact. The rocks above it consist of variant sandstone, clay, and coal beds tliat lie exposed in the low hills and ridges east of the main scarp. The Black Buttes coal group only in the northern two-thirds of the east side of the domo and nowhere in tlie Rock Springs field does the entire group outcrop. The upper portion is concealed by overlap of the Black Rock coal group. In the southern ))art of the field, the Black Buttes coal group is exposed only for a distance of 12 miles southwest of Black Buttes. On the south and west sides of the dome this group ia concealed and the Black Rock coal group rests unconformably in turn upon Ijewis shale, the Almontl coal group, and the white sandstone like that at Point of ]rocks, lying between the Almond and Rock Springs coal groups, and at one place (in T. 15 N., R. 105 W.) upon the Rock Springs coal group. Considerable ]>rospecting has been done at various places along this coal zone and good beds of coal are expose}. Near Black Buttes station the Union Pacific Railroad

Southern Hock Springs Coal Field, Wyoming. 233

Company opened a mine in 1868 which was worked for a time and then abandoned. The old Hall mine," 2 miles south of Hallville station, after being worked a few years was abandoned, as the coal was not BO good as that mined at Rock Springs. During the summer of 1907 a mine was opened in these beds trdles southwest of Black Buttes station and coal from it was placed on the market in 1908.

The following sections taken along the outcrop illustrate the thickness and character of the coal beds in the Black Buttes coal group:

Seetiont of coal bedt ir

Loralloa.

Sllonor™a1bl.

Section of coal bsd.

Quarter.

Sec

T. R. It 101

Is

R. loo

BW.lBW.l-

Coal s a'

HE-iNW.i.

Id

NE.iNW.t,

U

It 1 101

Cool a 2

aodibale IS Uul S

NE.iNVV.l.|il

u

J7

Coal 6 4

is

in)

NE.lNE.i.

ioi

Sandalone,

Ne.Ink.!,

Shale bd

SE.INE. i.

2a

Coal 10

B

lOd

toil 1

Ke. 1 Be. 1-

Nf-Ine.].

31)

Is

u

Im

,.

Bont 1

Co.] a

S 81

.v::. li

B 51

ao

i0

Be. 1 Ne. 1.

Is

Shale! !!X i

se; : :-

5 Si

aw. i Nw. i

Is

Job

BW.lSW.l.

Btinle

Coal a

Shale 3

Coal 2

coai:::::: 3

Coal a 8

30 in

234 CONTBIBUTIOSS TO ECONOMIC aBOLOQT, 1O06, PABI n.

Section or owl bed.

Loctlon.

Quwter.

T.

Iw

Sao.

T.

R.

8W.iNE.t.

ia

COBl 1

8W. 1 Be. (.

Is

If

m

n. la.

Ho

Is

10)

Sw. 1 Ne. 1.

Co.1 0 8

Ne. 1 Be. 1.

NW.lNCi.

too

Is

e St

T 101

Be. 1 Sb. 1.

NW.lNE.i.

jl

lod

ShaK. Cokl i C

S.:::::jjI

Kmobs-Cbbkoebb Coal Okouf.

In the eastern part of this region, the Kuobe-Cherokee coaj group or "Upper Laramie" formation is separated from the "Laramie" formation by an unconformity. The base of the group consists of non coal-bearing beds composed of soft shalo and brown conglomeratic sandstone, probably constituting the base of the Tertiary system. In other places this coal group is apparently conformable with the "Laramie." In part of the Great Divide Basin it b coal bearing in both the lower and upper portions. Coal beds in the Knobs-Cherokee coal group are present on the west side of the Rawlins dome and probably occur along the east side of the Rock Springs dome. They are, however, concealed by the overlap of the Black Rock coal bods. At best the location or even the presence of the base of these beds along the east side of the Rock Springs dome can only inferred, Forfurther information the reader is referred to Bulletin 341."

At Cheroke* Siding, in sec. 10, T, 20 N., R. 91 W., a prospect slope was driven down on a dip of 7° to a distance of 75 feet. At the old Fillmore station, in sec. 31, T. 21 N., R. 90 W,, in an artesian well drilled by the Union Pacific Railroad Company, a 20-foot bed of coal was reported at a depth of 220 feet, a 10-foot bed at 270 feet, and a 15-foot bed at 320 feet. At Wamsutter, in sec. 34, T. 20 N., R. 94 W.,

oSmlth, E. E., BulJ. U. S. Oeo

141, ISOe, pp. 233-334.

Southern Rock Springs Coal Field, Wyoming.

several artesian wells were drilled by the Union Pacific Railroad Company to supply water for the railroad. In well No. 2 three beds passed through between 1,045 and 1,145 feet are considered as belonging to the same horizon as the four Cherokee coal beds described in T. 20 N., R. 91 W. The exact base of the Wasatch can not be determined from the Wamsutter well records, but from a careful consideration of the facts noted in the field and the relation of the coal beds that outcrop just north of Wamsutter and Latham it is believed that all the coal beds mentioned in the drill record below a depth of 150 feet belong to the Knobs-Cherokee coal group or Upper Laramie'' formation.

Record of Union Pacific Railroad wells at Wamsutter.

Well No. 2.

Clay

Sh and small beds of coal

Shale

Sandstone

Shale, black and gray

Coal

Shale

Coal

Shale, gray

Strata, hard

Shale

Sandstone

Shale, gray and brown

Sandstone

Coal

Shale

Thickness.

Feet.

G5

Depth.

Feet.

Strata, hard ,

Shale, gray

Sandstone

Shale, gray ,

Sandstone

Shale, black

Sandstone

Shale, black

Sandstone, hard

Shale

Sandstone, soft ,

Shale

Sandstone

Shale

Coal

Shale, black and gray

Thickness.

Depth.

Feet.

Feet.

5S0

1,052

1,085

Well No. 3.

Soil or surface deposit

Sandstone, brown, very soft

Coal, small bed

Shale, light colored

Sandstone, brown, very hard

Shale, light colored

Chalk, cream colored, and soapstone

Coal

Shale, light gray

Rock, hard

Rock, soft, chalklike

Coal

Thicknass.

Depth.

Feet.

Feet.

1G5

Thickness.

Depth.

Rock, light gray

Uock, very hard

Shale, light gray

Rock, dark brown

Coal

Rock, dark brown

Shale, light gray , somewhat gritty . Rock, dark brown, hard and

tough

Coal

Sandstone, brown

Coal

Shale

Feet.

Feet.

The thickness of these beds at Wamsutter is probably 9,400 feet, and this is believed to be the entire thickness of the formation, as this place is very near the synclinal axis between the Rawlins and Rock Springs uplifts. For a description of sections along the outcrop of this formation illustrating the character and thickness of the

236 Contributions To Economic Geology, 1908, Part Ii.

coal beds, the reader is referred to the reports on the Great Divide Basin coal field and the western part of the Little Snake River coal field.''

Black Rock Coal Group.

The Black Rock coal group is thought to be of Fort Union age, but in this region the beds as a whole constitute the lowest member of the Wasatch formation, which here consists of three separate and distin units. At the base of the coal group is a thin band of conglomerate, ranging in thickness from 2 to 6 feet near the central part of the dome and increasing in thickness northward. The pebbles are very small, consisting mostly of quartz, although in many places pebbles of other materials are present. This conglomerate marks an unconformable contact between this coal group and the Black Buttes coal group. Ldthologically this coal group resembles the upper part of the Black Buttes coal group, but is on the whole whiter and more conglomeratic. The sandstone and shale, however, are more highly colored and more poorly cemented alid contain a large number of spherical and irregular concretions. Slag due to the burning of coal beds was observed at several places in this field, but as a rule it is of very small extent compared with the material affected by the burning.

The Black Rock coal group consists of two members. The lower member is made up of light-gray sandy shale, with beds of much darker sandstone. The sandstone is medium grained, brown, and cross-bedded. Many of the beds of sandstone are concretionary and chip into small conchoidal fragments, resembling chert chips, and do not form pronounced ledges. The beds are rich in fossils and are the source of the best plant collections made in this field.

The lower portion of the upper member consists of massive brown sandstone interbedded with light and dark shales. The middle and upper portions of the member are predominantly shaly and have a rather decided greenish tinge. In the upper part of the member occurs a somewhat harder sandy shale which is one of the ledges of a well-marked scarp in this part of the field. In tliis ledge are found numerous plants which are pronounced by F. H. Knowlton to be of Fort Union age. Thin layers of sandstone with abundant gastropods are found in ledges of the scarp and a few feet below are several thin bands of low-grade bituminous coal.

According to the blueprints of the Union Pacific Railroad Company a well was drilled in these beds at Table Rock to a depth of 1,402 feet. The only record available states that the well was drilled in 1881 and gives the strata passed through to a depth of 550 feet. At a depth of 435 feet the record shows coal 15 feet thick. As no description of the beds at a greater depth than 550 feet is available,

a Smith, K. E., Bull. U. S. Geol. Survey No. 341, 1909, pp. 233-234. tBall, M. W., Idem, pp. 252-253.

Southern Rock Springs Coal. Field, Wyoming. 237

nothing further can be said regarding the coal beds that are supposed to occur in the Black Rock coal group in this part of the field. Wells were drilled by the Union Pacific Railroad Company at Red Desert, in sec. 6, T. 19 N., R. 95 W., and Bitter Creek, in sec. 10, T. 18 N., R. 99 W. The Red Desert well was drilled to a depth of 1,116 feet and Bitter Creek well to 696 feet. No coal was reported in either well; but at a depth of 546 feet in the Bitter Creek well the retuml gives 9 feet of rich petroleum shale. The wells were drilled by chum drills, and it is possible that the coal may have escaped notice or wim pot recorded in the logs. It does not seem probable that all ihn coal beds are thin or absent at so short a distance back from th outcrop on the east side of the Rock Springs dome.

The lower half of the Black Rock coal group in richly some of the coal beds having a thickness of 25 'Dm luml on the east side of the dome lie nearly horizmtal; ihfmtt tm wiet side dip from 5° to 25® W. Not a few ouicrifjm of <'/al \f4ulH iu iUm group are concealed by a large amount of bumiJ irmUnL At Vhrioim places throughout the field coal is burning nhmif tmUrop nl ib# present time. Coal for local ranh nm in \mn% uiiuM iti prospect in sec. 24, T. 23 X., R. 104 W,, aiid at Mmkihtuy fttiim in sec. 13, T. 15 X., K. 105 W., and Uf a Utm ni mutm of other prospects in this group.

The eastern boundary of thw t-nd Z4aut in drrif/.i U$ rtfHftiM on the Great Divide Baian fwfW, aii/i tJM? little Htmiu*. llivtr fful field already cited-* TTm? nMme f:nd pntmih ovtfr h ItirifM liiritory in the soutbeaotem part of il0: lUik pnn'j fiH, 'ntffyih'/ a considerable area in tlte \ Crk t/wtih. O/aU ar kfi/wu Up outcrop in many parU of thi* \fiikmn in MxiSim part of Wyofuinif been mapped defmiUf sUAfWfiUth ea fvA iMt fsiM4/n itiifh group and its xlc hH&sj. wt of tli 'y/aJ foufi4 in thi group around tl iWrk Sj/fiit K K. bfjxitb ://lUyt:Ui4 a fcaf/i* line into CV/k/ndo aaud ik* zyjiifA m xh i/w kYiMsiiujul trough between tbre wrjih *fik*i xi ii/j:k rypnixpt aid xij uonh fiajok observed tita: fi*- K:fc*;i: K'x-k o'aJ vup M,*utiia ard. reiiij?

238 CONTBIBUTIONS TO EGONOUtC GEOLOGT, 1906, FABT II.

The following representative sections taken along the outcrop of the coal beds at various places around the dome illustrate their thickness and character:

Sectimu ofeoal beds in the Black Rock coal group in Che southtm pari of the Rock Springi field, Wyoming."

T. ' It.

Quuter.

K

T.

loa

MB. i aw, I.

Owl 1

NE.lNW.i.

SW.lBW.i.

S

14 101

ShidB. brown

Stalk, brown a

KK.iNW.i

Is

im

8W.1Ne.1.

,.

NE.iVW.i.

S '

Cod 3 0

Itt

!

"

Ne.Ine.J.

a

,.

™

Cod B

ax. i Htc. I

"

m

Cod 1 fi

WW.iMw.j.

sa

ll

Cosl 3

BW,iNW,i.

Ifi

„,

8hiiic,broo i

t-hitt. ""'

S g'

SW-iNW-i.

"

Borw!!;:!! 1 cod 3 l'

He. 1 Mb. 1.

„

fmd a 6

8hlo, brown.

NW.iSW.l.

J,„

ShBlt. l.lcir.

4 B

'

Cod 1 B

Ne. 1 Sw. ).

1 hrown 10

' 9hiilF. brown 3

, i'(wi B e

"i"

rod 1 B

1 1 m

ShiuS,broi(; 15

HE. i aK. i.

Cod 4

cod 1 11

1 1

4 B

NW. iSK. 1.

N-W.IN-W.i

Cod 1 6

none I

Conl a 7

HI nutthem irarl ot ilie

k neld sec Hull. V. S

Socthebn Bock Spbinos Coal Field, Wyominq. 239

Settwnt of ami bedt in Ike Btack Rofk tool pfoup tn llie toidhem part 0/ the Rock Spring* field, Wyoming— i!oalinm:(\.

T.

R.

Sk

T.

K.

SW. i NE, I.

NW.lNE.l.

Is

"

'j Sbole.

Shale,

BE. I SE. i.

NE.JNE.l.

.,

„

gfc!!!! ? S Coal S

Sw. 1 Ne. ).

.'

NW.lNW.l.

"

,.

,.

ew.iNE.i.

los

SSi.,.™ S

Ne. 1 He. 1.

'

,.

lOE

Coal a 7

DDao 1

Coal 3 a

"

Coal 1 1

a G

Jte. 1 8E. J.

aW.JSK.i

,.

lu

Sudiunc. I Coal a I

ao

„

' in

SW.lNW.l.

8E. i SW. 1.

,.

Coal 10

Coal 8

NE.i8W.l.

,.

i S""-" 1 '

Nw.18W.1.

,.

Coal a

Coal.!!.!!!! a s

Ne.Isw. 1.

Ib

w

Coal 4

Btial* 1 4

Coal 1 fl

3 a

Sw. I He. 1.

,.

,.

Coil 3 10

Bone a

coal 7

a B

SW.JNW.i.

Ib

Coal 4

Shal* 1 I

8E. 1 Se. I.

1*4

coai!!!!!!!! 7 10

SE. i SE. 1.

H

ino

, Cod!!!!!!! a 6

™

ae. I SW, i.

„

,.

™

Shalr 4 T

Is 10

E. 1 Ke. 1.

Coal 10

240 Contbibutions To Economic Geology, 1908. Part U.

The Coal.

Physical Properties.

The Rock Springs coal is jet black as it comes from the mine, has a bright or even glassy luster, and in places shows iridescent colors. The structure of the bedding planes is as a rule well preserved, but jointing is not strongly developed. The coal is dense in texture and somewhat brittle. The streak ranges in color from brownish black to black. Many slickensided surfaces are present in this coal, as well as numerous faults. Considerable deposits of salts occur on the faces of the coal and on the sandstone along the entries in the mines. The coal on exposure to the air remains firm and compact and stands shipping without breaking down. On burning it no clinker and leaves a small bulk of red-white or reddish ash. Samples taken from surface prospects and placed in air-tight cans soon lose their bright luster and the surface becomes covered with a velvety-brown coating, which is probably due to the alteration of the weathered coal. The chief impurities of the coal are sulphur balls and small lenses of pyrite that are scattered somewhat irregularly through the bed.

The higher coals are also distinctly black, with a bright luster as they come from the mine. They show more traces of iron stain than the Rock Springs coal and contain considerable gypsum and salt flakes in the joints or beddhig planes. On exposure to the air they alter more readily than the lower coals, lose their bright luster, and become a dull black. As they break down cracks fonn along and perpendicular to the bedding planes, producing somewhat regular blocks instead of the irregidar pieces resulting from conchoidal fracture. These coals somewhat resemble the Adaviile coal of Uinta County, but the}" seem to bo affected less on exposure to the air and their fractures and joints are more regular and quite different from the conchoidal fracture of the Adaviile coal.

Chemical Properties.

On account of the slight amount of development work done in the southern part of the field it was not possible to obtain many representative samples of the coal for cliemical analysis. Eleven samples were taken, but only one of these (Xo. 6672) was obtained from a fresh face of coal in an operating min(. Most of the samples were collected near weathered surfaces, from old abandoned prospects, and the coals were probably more or less altered. Most of the prospects from wliicli samples were taken have been opened sufficiently to pass through the weathered zone near the surface, but deterioration in these ])laces is in part due to the action of air on the walls of the coal in the prospect pit since the opening was made. Besides the eleven samples above mentioned, fifteen additional

Southern Rock Springs Coal Field, Wyoming. 241

samples were collected to show the various stages of weathermg or the depth to which weathering affects the chemical composition of the coal. Five samples were collected from the Rock Springs coal at the Gimn mine; five from the Almond coal at the mine east of Point of Rocks, and five from the Black Buttes coal southwest of Black Buttes. These are described in the next paper in this bulletin (pp. 282-296).

Representative samples of coal were collected from the four coal groups wherever good coal could be obtained and were sent in airtight cans to the chemical laboratory of the fuel-testing plant at Pittsburg, Pa., for analysis."

In order that the results from the samples collected might be entirely comparable, all sampling was done in accordance with the general plan adopted by the fuel-testing plant.''

The accompanying table gives the result of analysis of (1) samples as received in the laboratory, containing all the moisture that is present in the coal in the mine; (2) air-dried coal, after part of the moisture that is easily separated has been expelled; (3) dry coal, after the moisture has all been eliminated, and (4) pure coal, after the moisture and ash have been eliminated. The analyses are grouped according to the calorific values, the coal having the highest British thermal unit value in the air-dried sample heading the list for each of the four groups.

a For analyses of coal sampled in the northern part of the Rock Springs field in 1907 see Bull U. 8. Geol. Survey No. 341, 1909, pp. 270-273. Bull. U. 8. Oeol. Survey No. 341, 1909, pp. 12-13.

79G3"— Bull. 381—10 16

242 Contkibutions To Economic Oeology, 1908, Pabt Ii.

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244 Contributions To Economic Geology, 1908, Pabt H.

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Coal bed.

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Bouthern Sock Spbinqs Coal Field, Wyminq. 245

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246 CONTBIBJJTIONS TO ECONOMIC GEOLOGY, 1908, PART II. Samples of coal from the Rock Springs coalfield, Wyoming.

Laboratory No.

G795

Name of mine.

Wyoming Coal and Coke Co.

Gunn-Quealy

Gunn-Quealy

Gunn-Quealy

Gunn-Quealy

Kent

Gunn-Quealy

Kappes

Rock Sprlnes-Wyo- Coal Co.

Rock Springs- Wyoming Coal Co.

Rock Springs- Wyoming Coal Co.

Rock Sprlnes-Wyoming Coal Co.

Prospect

Rock Springs-Wyoming Coal Co.

Rock Springs-Gibraltar Coal Co.

Rock Springs-Gibraltar Coal Co.

Rock Springs-Gibraltar Coal Co.

Rock Springs-Gibraltar Coal Co.

Rock Springs-Gibraltar Coal Co.

Menkinney

Canyon Creek pros-

IM'Vt.

I*ro.sp*'ct

Sampling point.

Second entry south. 20 feet north of fault.

1,100 feet from mouth .

800 feet down slope

80 feet down slope

40 feet from entrance. .

150 feet from surface. . .

75 feet from opening, south entry.

10 feet down slope

40 feet entrance. .

300 feet in from opening,

1,000 feet in from opening-

500 feet in from opening.

300 feet west of opening

30 feet from opening. . .

150 feet in from open- Inc.

100 feet down slope

50 feet opening. . .

355 feet from opening

down dip. 150 feet from opening

down dip. 225 feet from opening

down dip. 100 feet from opening

down dip. 50 feet from opening

down dip. 30 feet from opening. . . 54 feet west by 40 feet

south of 50 feet from o[)ening. . .

50 feet from opening. . .

Condition of sample.

Dry, unaltered

Dry, unaltered

Dry, unaltered

Weathered

Dry, unaltered

Dry, unaltered

Dry, unaltered

Dry. badly weathered.

Sligntly weathered

Dry, unaltered

Dry, unaltered

Dry, unaltered

Dry, weathered

Sliphtly weathered

Dry, unaltered

Dry, unaltered

Dry

Dry, unaltered

Dry, unaltered

Dry, unaltered

Dry, unaltered

Weathered

Dry, unaltered

Dry, unaltered

Slightly weathered. .

Dry, slightly weathered.

Sampler.

B. L. Johnaofi.

H. R. Lewis.

J. L. Rich.

J. L. Rich.

R. O. Bartholomew.

J. L. Rich.

R. O.

J. L. Rich.

R. O. Bartholomew.

B. L. Johnson.

B. L. Johnson.

B. L. Johnson.

B. L. Johnson. J. L. Rich. B. L. Johnson.

J. L. Rich. B. L. Johnson.

B. L. Johnsim.

B. L. Johnson.

B. L. Johnson.

B. L. Johnson.

B. L. Johnson.

U.Schnlti. B. L. Johnson.

E. K. Smith.

B. L. Johnson.

Burning Of Outcrop.

In the western coal fields many coal beds have been burned along their outcrop, and in a few places the burning is going on at the present time. The extent of the burning is in general inversely proportional to the value of the coal.

In the Rock Springs field the amount of burning is relatively small in the Rock Springs and Almond coal groups and a little more prominent in each of the other coal groups, being most pronounced in the Black Rock. Considering the amount of burning that has been going on, tlie slag accumulations are small and as the coal burns without leaving much clinker. In some ])laces the efTect on the adjacent rocks can be seen several feet from the actual seat of the burning; in other ])laces rocks a very short distance away are not affected. The appearance of the coal bed near the burning or ])urned bed does not seem to !)e altered by the burning. On the other hand, the chemical analyses usually show decided diflferences

Southebn Rock Springs Coal Field, Wyomikg. 247

between coal from the immediate vicinity of the burned or burning bed and similar coals collected from the same group at more remote distances. The coal taken near a burned area has become of considerably higher grade than the unaffected coal, having as a rule a higher British thermal unit value, lower air-drying loss, low volatile matter and high fixed carbon, and, in the ultimate analysis, high carbon and low hydrogen and oxygen. In this connection a comparison of analysis No. 5299 with Nos. 5298, 5432, 5448, and 5447, representing the same group of coals, is interesting.

Quality Of Coal.

The lower coals of the Rock Springs coal group stand shipment well and do not slack on exposure to the air. They belong in the bituminous, noncoking class of coals. The coal of the Almond coal group is physically and chemically more closely related to the coals of the Black Buttes, Knobs-Cherokee, and Black Rock coal groups than to the Rock Springs coal. The chief difference is that all the coals above the Rock Springs coal group have more moisture and are lighter in weight than those of the Rock Springs and slack considerably on exposure to the air. These coals fall in the lowest grade of bituminous or the highest grade of subbituminous coals. As a rule they are better than the Adaville and Evanston coals of southern Uinta County. The coals of the Rock Springs field have a low sulphur content which ranges from 0.30 to 5.88 per cent, but is usually less than 1 per cent, averaging 0.84 per cent for the entire 85 samples collected. The coal beds in the four coal groups (Rock Springs, Almond, Black Buttes, and Black Rock) give comparatively clean coal and have a low content of ashj ranging from 1.51 to 17.41 per cent and averaging 5.43 per cent for the 85 samples collected.

The following table may be considered as representing the average condition of the coal in the five groups of coal beds. The table shows the relative values of these coals with respect to ash, sulplnir, carbon, and fixed carbon. The Black Rock coals have the greatest amount of ash and sulphur, and in this respect as well as in their carbon content are only a little poorer than the Knobs-Cherokee coals. The Rock Springs and Black Buttes coals carry nearly the same amount of impurity and carbon.

a Ball, M. W., Bull. U. S. Qeol. Survey No. 341, 1909, p. 251.

248 Contributions To Economic Geology, 1908, Part Ii.

ValtLcs of air-dried coal in the various coal groups in the Rock Springs coal field.

Coal group.

Black Rock.

Enobs-Cherokeo a .

Black Buttes.

Almond .

Rock Springs.

Number

of samples.

Maximum Minimum. Average.. Maximum Minimum. .Average.. Maximum Minimum. Average.. Maximum Minimum. .Average.. Maximum Minimum. Average..

Ash.

Sulphur.

Carbon.

Fixed carbon.

S2.78

aSmith, E. E. The eastern part of the Great Divide Basin coal field, Wyoming: Bull. U. S. Geol. Survey No. 341, 1909. p. 238. Bail, M. W., The western part of the Little Snake River coal field, Wyoming: Idem, p. 251. This coal group is not exposed in the Hock Springs dome, but is believed to be present.

As pointed out by David White," ash and oxygen are of nearly equal weight as impurities in coal with respect to heat efficiencies. On arranging the values of the samples obtained in the Rock Springs field according to the ratio C (O + ash) it is found that these values have approximately the same order as the efficiencies determined calorimetrically. Although the order differs slightly from that of the British thermal unit values, the difference is small, the variation in thermal units being for the greater number of samples less than 100 and in few exceeding 500. Many of these samples were considerably weathered and it is remarkable that these ratios should correspond so closely with the determined British thermal unit values. From these analyses it appears that the ratio C-7-(0 + ash) furnishes a fairly satisfactory basis for grouping coals according to their heat efficiencies.

Comparative Values.

The cods of the Rock Springs coal group occur in the same geologic formation (the Mosavordo) as the bituminous coals of the Yampa, Danfortli Hills, and Grand Hogback fields of Colorado and the Book Cliffs field of Utah, and compare favorably with those coals. They are not so good as the Kommoror coals (of Benton age) in Uinta County, Wvo., which show a tendency to coke and have a high heat efliciency.

Rock wSprings coal bed No. 7 was tested by the United States fuel-testing ])lant at St. Louis in 1900 for producer-gas and coking properties/ Two mine samples and one car sample of coal were

a The effect of oxyjL'cn in coal: Bull. V . S. Geol. Survey No. 382. 1909.

fcSchultz, A. R.. Bull. U. S. Geol. Survey No. aui. 1907, pp. 219-222. Veatch, A. C, Bull. U. S. Geol, Survey No. 285, 1900. pp. 33G-337. cSee " Wyoming No. 6," Bull. U. S. Oeol. Survey No. 332, 1908, pp. 28G-287.

Southern Rock Springs Coal Field, Wyoming.

taken for chemical analysis. The analyses, together with the results of the producer-gas and coking tests, are given here for the purpose of comparison. Samples 3164 and 3165 were taken in the mine 5,200 and 7,000 feet north of the foot of the slope, and the coal bed at these places measured, respectively, 7 feet 6 inches and 7 feet 2 inches in thickness.

Analyses of Rock Springs coal as received from bed No. 7. Rock Springs Wyo.

Laboratory No

Alr-drying loss

Proximate:

Moisture

Volatile matter.

Fixed carbon...

Ash

Sulphur

Ultimate:

Hydrogen

Carbon

Mine samples.

Nitrogen

Oxygen

Calorific value (as received):

Calories

British thermal units

6,(;22 11,920

Car sample.

6,538 11,768

Producer-gas test of Rock Springs coal (run-of-mine) from bed No. 7, Rock Springs.

Coal Consumed In Producer Per Horsepower Per Hour (Pounds).

Per electrical horsepower:

Commerciall V available . .

Developed ai switchboard Per brake horsepower:

Commerciall V available. . .

Developed at engine

Coal as fired.

Dry coal.

Combusti- ble.

Analyses.

Coal.

Moisture 11. 44

Volatile matter 36.37

Fixed carbon 48. 49

Ash 3.70

Sulphur 91

Oas.

Carbon dioxide (COj) 10. 1

Carbon monoxide (CO) 20. 4

Hydrogen (Ha) 18. 2

Methane (CH,) 2. 6

Nitrogen (No) 48. 3

Ethylene (C2H4) 4

Duration of test, fifty hours. Average electrical horsepower, 194.5. Average British thermal units per cubic foot of gas, 168. Total coal fired, 15,600 pounds.

Coking test of Rock Springs coal from bed No. 7, Rock Springs, Wyo.

Size as used: Raw, finely crushed. Duration of test, thirty-nine hours. Coal charged, 8,000 pounds. Coke produced, none. Analysis of coal: Moisture, 11.09; volatile matter, 34.53; fixed carbon, 50.50; ash, 3.88; sulphur, 0.84.

250 Contributions To Economic Geology, 1906, Part H.

The Rock Springs coal as a locomotive fuel or steam coal has few superiors in the West. It bums under a forced draft without heavy sparking and is a quick steamer, leaving only a small quantity of ash. Although the coals of the Almond, Black Buttes, and Black Rocks coal groups have been mined and prospected very little in the past, the future no doubt will see extensive mining on all these coal beds. During the summers of 1907 and 1908 two mines were opened on coal beds of the Almond and Black Buttes groups and coal is now being shipped from them. The coal from these beds is no doubt much like the ' ' Upper Laramie '' coals of the Hanna field, and there is no apparent reason why it should not serve as well as most of the Carbon County, Sheridan (Wyo.), and Montana coals, which are at present extensivdy and satisfactorily used for firing locomotives on the Union Pacific and Burlington railroads. Although the coal is very light for such work, it has proved very successful when used under natural draft for heating purposes and a large trade in it has been developed.

History Of Development. Prospecting And Mining.

Coal was discovered in Wyoming prior to 1834 on Belle Fourche River, but the first coal mine was opened at Coal Bank Hollow, near Rock Oeek crossing, in Carbon County, where the Denver and Salt Lake stage company utilized the coal for fuel and blacksmithing purposes. Mining on a commercial scale, however, did not begin until the construction of the Union Pacific Railroad across Wyoming in 1X67, 1808, and 1809. Prospecting for coal along the route of this road commenced in 1807, and coal was opened at Carbon, Point of Rocks, and Rock Springs early in 1868. The Carbon mines in 1868 the first Wyoming coal used by the railroad company. During August of that year the production amounted to 650 tons. A few months later tlie Rock Springs and Point of Rocks mines were ready for operation. The total coal of Wyoming in 1868 was 0,925 short tons. The output for 1869 was as follows:

Cnal profluction in Wyomiyig, 1S69.<

Tods.

Carbon 30, 428

16, 903

Point of Hocks 5, 426

Evanston (A liny) 4, 439

Other 990

58, 186

The above figures are slightly diflferent from those generally reported and given in the 'Mineral resources of the Ignited vStates" — 49,382

Uuyinond, K. W., Mineral resouifes west of the Kocky Mountaius, 1872, pp. 370-371.

Southern Rock Springs Coal Field, Wyoming. 251

tons. This discrepancy arises mainly from the fact that the product of the Point of Rocks mine and 2,473 tons mined by the Rocky Mountain Coal and Iron Company at Evanston are generally omitted from the reports. In forty-one years coal mining has developed into the leading industry in Wyoming, with an annual production of over 6,000,000 tons, valued at approximately $10,000,000, of which onethird comes from the Rock Springs field. The rapid construction of railways and the ever-increasing demand for fuel in this and adjoining States will make coal mining Wyoming's greatest enterprise for many years to come.

From the completion of the Union Pacific Railroad in 1869 to the construction of the Superior branch up Horsethief Canyon in 1906 all the mining camps in the Rock Springs field, except the Sweetwater camp south of Rock Springs, were opened along the railroad in Bitter Creek valley at distances of less than a mile from the main line. Although the entire Rock Springs field has been fairly well prospected, thus far only four districts — Rock Springs, Superior, Point of Rocks, and Black Buttes — are producing coal. All the mining camps within these four districts are less than 10 miles from the main line of the Union Pacific Railroad.

ROCK SPRINGS DISTRICT. DESCRIPTION OF COAL BEDS AND OUTLINE OF DEVELOPMENT.

The Rock Springs district is by far the oldest, largest, and best developed in the field. It includes all the coal-bearing beds north and south of Bitter Creek valley on the west side of the dome in the vicinity of Rock Springs, or that part of Little Bitter Creek and Killpecker valleys whose source of supply and transportation centers about Rock Springs. Within this district have been opened seven mining camps — Rock Springs, Sweetwater, Blairtown, No. 6, Interstate, Van Dyke, and Gunn — most of which are still in active operation. In each of thee camps, except the No. 6 and Interstate, there is one or more active operating mines at the present time. Of the four coal groups exposed in the Rock Springs dome, three (Rock Springs, Almond, and Black Rock) are exposed in the Rock Springs district. Mines have been opened on coal beds in each of these groups, but at present only the mines working on the coal beds in the Rock Springs coal group are in active operation. Several coal beds occur in the Black Rock and Almond coal groups in the Rock Springs district (see PI. XFV), but thus far none of these beds have been profitably mined.

The total number of coal beds in the Rock Springs coal group has not been determined. Twenty beds that range in thickness from 2 to 12 feet are known: and it is certain that there are maivy bAs.X'ss.

252 Contributions To Economic Geology, 1908, Pabt Ii.

than 2 feet thick. One section taken across this group shows 37 distinct coal beds. That the number and thickness of the coal beds differ considerably at different points along the bed is equally certain. On being traced along the outcrop many of the larger beds are seen to become thinner and many of the thin beds to become thicker and workable. On the whole, the coal beds of this group are fairly persistent and regular. Of the large number of beds exposed in the hilla on either side of Bitter Creek in the vicinity of Rock Springs, only five of the best have thus far been considered large enough to be worked.

Owing to the general practice of numbering mines according to the sequence in which they are opened by the company and later naming each coal bed after some prominent mine upon it, the designations of the Rock Springs coal beds, though in numerals, give no information regarding the stratigraphic order in which they occur.

All the mines in the Rock Springs district are located in Tps. 18 and 19 N., Rs. 104 and 105 W. The Sweetwater mine No. 1, in sec. 14, T. 18 N., R. 105 W., is the southernmost and the Gunnmine, in sec. 8, T. 19 N., R. 10*4 W., is the northernmost of the productive mines in this district. East-west lines drawn through the extreme north and south workings of these two mines would be only 7 miles apart. All the workings of the other mines in the district lie between these two, in a belt less than 5 miles wide. The five coal beds of the Rock Springs coal group on which mines have been opened in this district, together with their respective mines, are given in the following table in their proper stratigraphic sequence:

Bouthebh Boce Spbinob Coai. Field, Wyoming.

t i

S 1

s &

1 ?

Mi ii. il. i

1 III 4ii fii f i I

1 ill m

'

1 1 1

i

:? 1

; 1 ;

e 1

o

1 m Mil iiiss|| J 1 y

lilPtiPiiii i 1 III III! iiiilllll t fl"

s

%

S3S S3Ss 333S393S S Z S S

St S22 22S2 2222SS222S 3 3 2 3

ss- asa" assa=ii!a"= - - s -

i i ii ; i : i : : i : : i

i Hi iiii 1 Mii i i i

"§s nf n sp

n : :

;

:?

E i 1

Ui

:l5

£ .5

$

254 Contbibutions To Economic Geology, 1908, Pabt H.

That the five coal beds mentioned above are by no means the only ones in the Rock Springs coal group is best brought out by the following section, furnished to the writer by the Union Pacific Coal Company:

Section of the Rock Springs coal group in the Rock Springs district showing the stratigraphic succession of the various coal beds as determined by the Union Pacific Coal Company.

Order of

coal beds.

Local

name

of coal

bed.

Distance

from top

of group

to base

of coal

bed.

Section of beds.

Thickness of coal.

Ft. in.

4 ' 178

7 No. 3 248

9 27S

10 414

Shale

Coal, shaly

Clay

2 fl

Coal

Clay

Coal

fi

Clav .

Shale

11 6

Sandstone

Coal, bony

Shale

Coal

Q

Shale

Sandstone

Coal

Clay

Coal

Shale

Clay and coal

Sandstone

Shale

Sandstone

C/J

Shale

Sandstone

Clav and

Coal, shal V

1 fi

Clav

Sandslono

Ik

Clav and coal

Sandstone

Clav and coal

Sandstone

Shale

Coal

7 a

Coal clav

5 0

Sandstone

f)

(Mav

Sandstone

Coal

Clav and coal

1 2

Sandstone

Shale

Sandstone

Clav and coal

1 fi

Saixlstone

7

Sandst one

Clav

Sandstone

<i7

Coal and olav

Ft. in. Ft. in.

Distance from base of cool bed to base of next underlviM ooalDed.

Ft. in,

Bouthebn Bock Sfbinos Coal Field, Wyomikg. 255

Stdion of tlu Roet $ coal group in Uit Rock dutriet, ihowmg ilu itratigraphic rueaitum of iht voriout eoai iMilt at dtUrmxnid by CJU union Pacific Coat

Co mpaiiy — o Qtin ue J .

of

Local

Dlitoac* from lop

MM or

oiwlbeci tabMOl

No. I

FL to.

in 11

n. in.

Ft. In.

f(. in.

U

m t

.„

1 e

'

tea

'

Orb

n e

, .

°Si.ii

'

Cm] S

„

m

M I

ta a

Jr

J..

IS n

au 10

Cool

E

8M lOJ

U 9

a

T

eu

3 11 la 8

"

O

m i

Coia B

256 Contributions To Economic Geology, 1908, Pabt Ii.

Section of the Rock Springe coal group in the Rock Springe dietrict, ehowina the itratigraphic eucceeeion of the varioue coal beds as determined by the Union Padfic Coal Companyntmxied .

Order of

ooal beds.

Local

name

of coal

bed.

II or

Upper

Van

Dyke

Distance

from top

of group

to Dase

of coal

bed.

Ft. in.

Section of beds.

J

K

Van Dyke

M

N

r

063 11

Ft, in.

Sandstone 17 4

Coal 2 4

Thick-

neoiof

coal.

Ft. in.

Shale 10 7J

Coal

093 2

Sandstone, yellow 28 7

Coal 8

1 nn? Q ' Sandstone, yellow 12

i,W7 ; P--1 o

Coal

1,030 5

1,055 9

Sandstone, white 20 9

Coal 2 I

Distance from base of coal bed to base of next underlyi coal

a

Not recorded 20 6

Coal 7

Clay 6

Coal 3 10

1,124 9

Not recorded 66 7 I

Coal 1 2 1

Shale 11

Coal ! 4

1,133 9

Not recorded 8 8

Coal 4

Q I.Iso

Not recorded 12 8

Coal 6

Not recorded 9 1

Coal I

Not recorded 22 6

Coal 2

Shale 3

Coal 2

Shale 5

Coal 5

' 1 oil A '' Sandstone, vellow, and shale 30 1 , ,

36 S 1,250 2

37 T 1.27:) 8

Sandstone, white 47

Coal 10

Not 14 3

Coal 2 3

Shale.

Sandstone, nuissive. white: base of Kock Springs coal Rroup.

Total coal ! 110 6

Ft. in,

Of the five coal beds thus far opened, Nos. 1 and 7 have produced by far the hirgest amount of coal, and nearly as many mines have been opened on No. 7 as on all the other beds to;ether. On the Van Dyke hod two mines have been opened, one at Van Dyke and the other at Gunn. This bed as opened at the old Van Dyke workings averaged about 4 feet in thickness, and as a rule it is not less

Southebn Rock Springs Coal Field, Wyoming. 257

than 3 feet 8 inches nor more than 4 feet 2 mches thick. Overlying the Van Dyke bed is a group of beds which increase in size toward the north. About a mile north of the Van Dyke main entry there are openings upon three of these beds, two of them showing but 2 or 3 feet of coal, the third 4 feet 2 inches of very clean and bright coal. Still farther north, in sec. 8, T. 19 N., R. 104 W., on the western slope of Baxter Basin, two of the beds are at least 6 feet thick, a third about 4 feet, and several others smaller. In this section the Gunn-Quealy Coal Company opened its A and B mines, presumably 6n the lower and upper Van Dyke coal beds, respectively. Two of the larger coal beds have been opened about three-fourths of a mile farther north, where they are nearly 7 feet thick. These two beds are 40 feet apart and at least 200 feet lower than bed No. 7, which outcrops at the upper edge of the bluff forming the side of the basin.

Bed No. 7 has produced more coal than any other bed in the Rock Springs district, and, as shown by the description of the various camps, most of the producing mines are located on it. The coal bed shows considerable variation in thickness, but it is not over 10 feet thick in that part of the, district opened by mine workings. It is, however, remarkable in maintaining a workable thickness of clean coal, and this more than counterbalances its small size.

The Central Coal and Coke Company's No. 1 mine is the most southerly large opening on this bed. It is situated in Sweetwater Valley and the main entry begins near the center of sec. 14, T. 18 N., R. 105 W. The bed here is from 7 feet to 7 feet 6 inches thick, is wt' hout partings, and has an average dip of 7° to 8° N. 85° W. A stratum of impure clay only a few inches thick lies immediately below the coal, and below that is a firm, massive gray sandstone. Above the coal there is 10 feet of clay shale, and above that a reddish sandstone that is also very persistent.

A mile northeast of the Central Coal and Coke Company's No. 1 mine there are a series of shallow cuts on bed No. 7 that show 7 feet or so of clear coal. About 2 feet from the roof there are two* thin seams of clay, 2 J inches apart, each of which is from a quarter to half an inch thick. This double clay parting is uncommon, but a single parting of this character is generally present, the Central Coal and Coke Company's No. 1 mine being the only one that does not show it. The distance of this parting from the roof is about 2 feet, no matter what the thickness of the bed. Another peculiarity is the presence above the coal of a thin band consisting of alternate streaks of clayey matter and coal. This layer is from 2 to 5 inches thick, and when exposed to the air it soon scales down. Displacement along slips is well shown in one of the cuts referred to above. The two clay streaks show four small faults in a space of 20 inches.

7tl63°— Bull. 381—10 17

258 Contbibutions To Economic Geology, 1908, Part Ii.

The downthrow of these faults is (1) to south, 2 inches; (2) to south, 4 inches; (3) to north, 1 inch; (4) to south, inches. The inclination of the fault planes varies from 40° to 65° from the horizontal.

Along the outcrop of bed No. 7 toward Rock Springs the gray sandstone floor is in places very prominent and outcrops beyond the coal as a bare platform. Near the center of sec. 12, T. 18 N., R. 105 W. there are two faults approximately 700 feet apart. The movement of the block between these two faults was downward; the amount of displacement was not ascertained. Another displacement in bed No. 7 appears farther north, about 800 feet south of the west quarter corner of sec. 1, T. 18 N., R. 105 W. Here the bed is cut by a fault with a downthrow to the north of about 100 feet. This fault appears to have a general course of S. 60° W. and passes in this direction across the SE. sec. 2, T. 18 N., R. 105 W. Along the line of outcrop, not more than 1,400 feet north of the abovementioned corner, there is another fault with a displacement in the same direction probably amounting to 150 feet. This fault has a direction of about S. 75° W., and consequently diverges toward the west from the fault just described. It also passes into sec. 2. A peculiar feature of this fault is that it is lost to sight in the flat not far to the west, but along its general course, near the center of sec. 2, a fault is observed just north of the Klegg opening on bed No. 1, with an upthrow to the north of no great amount. Continuing on the same course, the fault is found to have a displacement of nearly 100 feet, with an upthrow to the north, as plainly shown on the outcrop of bed No. 3. The Wyoming Coal and Coke Company's mine, lying immediately nortli of this fault, shows no otlier serious displacement in that direction, and the continuous outcrop of the sandstone floor of bed No. 3 for some distance to the south indicates no disturbance in that direction. Consequently it appears either that the displacement shown on the outcrop of bed No. 7 makes a great change in its general course or that it rapidly decreases toward the west to a point wliere there is no disphicement and then shows an increasing throw in the opposite direction. An apparent greater dip of the strata on the south side of this fault might perhaps liclp to explain the phenomenon. The same results might be obtained by a slight distortion of the block between the two faults.

In an opening on bed No. 7, known as the Ludvigson mine or prospect, between the two faults just described, the bed contains 6 feet of coal of excellent quality. The clay parting, 2 feet from the roof, is about a quarter of an inch thick.

The next opening toward the north on bed No. 7 is in sec. 36, T. 19 N., K. 105 W., where the Central Coal and Coke Company has opened its No. 2 mine. The bed, as exposed in the two strike entries, shows

Southern Rock Springs Coal Field, Wyoming. 259

5 feet of clear coal, broken only by the usual parting above mentioned. The dip is from 7° to 9°, but the strike has swung a little to the west (N. 10° to 20° E.). The roof and floor aye of the usual character. The bed appears to have reached its minimum thickness of 4 feet 6 inches in this mine. The coal as a rule is very clean and pure. The normal clay parting is present. Near the eastern limit of the mine the streak of dirty coal and clay already referred to thickens and encroaches upon the upper bench of the coal. Other bands of carbonaceous clay appear lower down, but above the parting, and the entire upper 20 inches is worthless, in places leaving less than 3 feet of coal for mining. The poor coal is apparently confined to a narrow belt running in a northerly direction. Owing to the deep gulches in this section the outcrop is irregular and has never been accurately located. After crossing the main gulch near the center of the section it passes up a lateral ravine and, returning, swings in a bold curve across a high hill into the valley of Bitter Creek, on the north side of which the Union Pacific Coal Company's mines Nos. 7, 8, 9, and 10 are located.

North of Bitter Creek the Union Pacific Coal Company's mine No. 8 is a shaft about west of the No. 7 main entry. The coal appears to be of excellent quality in the workings and the bed is about 4 feet 8 inches thick.

North of mine No. 7, which extends nearly to the north end of T. 19 N., R. 105 W., several prospect entries have been excavated on the bed. Thus in the NW. i sec. 20, T. 19 N., R. 104 W., an entry 175 feet in length shows the bed to contain about 8 feet of coal, as shown in the following section :

Section in entry in NW. J sec. 20, T. 19 N., R. 104 W.

Sandstone, hard, rusty. Ft. In.

Shale, light, with siliceous band 9r±:

Shale, dark 2

Coal 2 4

Clay i

Coal 3 IJ

Shale, carbonaceous 5

Coal 2

Clay, carbonaceous 6

Sandstone, massive, gray.

Coal bed 7 lOJ

The coal is clear and bright and appears equal in every respect to that mined farther south. Another entry on the same bed starts near the top of the hills facing Baxter Basin in theSE. J sec. 8 of the same township. Though the entry is over 200 feet in length it attains no great depth beneath the surface, and the coal shows the softening due to surface action in some of the streaks between the

260 Contributions To Economic Geology, 1908, Part Ii.

slips. The bed contains 7 feet 6 inches of coal. The clay parting is about 2 feet from the top. There is no carbonaceous shale near the bottom, as noted in sec. 20. The dip is about 10® and the strike has swung back to almost due north.

Bed No. 7, as well as many of the others, has been traced for several miles north, and prospects have been opened on it and other beds. (For locations see Pis. XIV and XV.) It can not be stated with certainty that the bed No. 7 at Rock Springs is the same as bed No. 7 at Superior, although the Superior beds were correlated and named from the Rock Springs coal beds*. A comparison of the two sections of the Rock Springs coal group will show the relation between them.

Although the first coal mined at Rock Springs was taken from bed No. 1, the mines on it are closer together and less prospecting has been done along its on bed No. 7, so that at present it is notso well understood. It is apparent, however, that although the coal in bed No. 1 attains a maximum thickness greater than that of bed No. 7 the former bed is by no means so regular as the latter and apparently contains neither the area nor the quantity of coal that bed No. 7 contains. The most southerly mine opened on bed No. 1 is the old Blair mine, sometimes known as the Rock Springs Coal Company's mine No. 1, at present owned in part by the Wyoming Coal and Coke Company. Next north is the now abandoned Union Pacific Coal Company's mine No. 2, then the Union Pacific Coal Company's Nos. 1 and 4, the latter being the most northerly on this bed. At present all these mines except the Wyoming Coal and Coke Company's mine and the Union Pacific Coal Company's mine No. 1 are abandoned.

South of the old Blair mine there are several openings. The Klegg entry to the soutlieast, directly south of the fault from Rock Springs Coal Company's mine No. 1, shows 10 feet of coal. Another opening on the east side of Sweetwater Valley shows 9 feet of coal and one to the west about 4 feet 6 inches. Bed No. 1 has been traced for miles nortliward from Rock Springs, but no extensive workings have been opened on it north of that city.

Bed No. 3 has been only a little developed. Three mines are located on it and show coal of [good grade of from 6 feet to 7 feet 6 inclies in thickness. Two of these mines have been abandoned and the third is just being opened.

Very little prospecting has been done, and only one mine has been opened on bed No. 5, consequently little can be said regarding it. At the place the mine was opened the coal was found to be slaty and the mine was therefore soon abandoned, but the indications along the outcrop suggest that tliis bed ought to furnish good coal in parts of the district.

Southebn Rock Springs Coal Field, Wyoming. 261

Rock Springs Camp.

The Rock Springs mining camp was the first one opened in the Rock Springs district. Several companies have operated here, and two are still active. Some of the mines, as the Blair mine and those of the Rock Springs, Excelsior, and Peacock coal companies, have shut down ; others, as those of the Sweetwater Coal Mining Company, the Youngs mine, and the Klegg mine, have been consolidated with those of larger companies and are still producing. Mines in this camp have been opened on four beds of the Rock Springs coal group, Nos. 7, 1, 3, and 5. At present the only companies operating in the camp are the Union Pacific Coal Company and the Central Coal and Coke Company.

The Union Pacific Coal Company has opened mines Nos. 1, 2, 3, 4, old No. 5, 5, 7, 8, 9, and 10. Of these mines Nos. 7, 8, 9, and 10 were opened on bed No. 7; Nos. 1, 2, and 4 on bed No. 1; Nos. 3 and 5 on bed No. 3, and old No. 5 on bed No. 5. At present this company is working only beds Nos. 1 and 7. Mine No. 1 is working bed No. 1, and mines Nos. 7, 8, 9, and 10 are working bed No. 7. The Central Coal and Coke Company is working at present in this camp only bed No. 7, on which is located its No. 2 mine.

Union Pacific Coal Company s mine No. 1, — The Union Pacific Coal Companys mine No. 1 was opened in 1868 and is still producing. It is operated by a 7,500-foot double-track slope on the dip of the coal, which is about 5° at the outcrop, but steepens to 23° near the bottom of the slope. The direction of the dip and slope is a little north of west. Entries extend along the strike on either side, with rooms driven to the rise, parallel to the slope.

A peculiarity developed at many places in the workings of mine No. 1, but also common to the other mines on the same bed, consists of the so-called rock slips or horsebacks. These are long, slim wedges of white sandstone which protrude into the coal, usually from the floor. They have commonly a polished surface on one side and a rough surface to which the coal adheres on the other. Some of them extend only a few inches from the floor; others almost or quite to the roof of the bed. They are very narrow, being at most only a few feet wide at the base, and gradually wedge out. Longitudinally many of them extend for many yards. There appears to be no regularity in the direction in which they run or the frequency of their occurrence. The coal is of the normal quality, even where it is in direct contact with the pure sandstone.

262 Contributions To Economic Geology, 1908, Pabt Ii.

The roof of this mine is usually shale and the floor brown or white sandstone. In all the lower entries 20 inches or 2 feet of coal is left for a roof. The section in this part of the mine is as follows:

Sectixm of coal bed in mine No. 1 of the Union Pacific Coal Company at Rock Springs,

Shale (roof). Ft. in.

Coal (not mined in lower entries) 1 10

Coal, bony 9

Coal, good (mined and sampled) 7-8

Sandstone (floor).

A number of faults are present in this mine, which is in part bounded on the east and southeast by two faults, each with a maximum displacement between 65 and 70 feet and a downthrow toward the mine. These two faults probably intersect a short distance southeast of the mouth of the main slope. The one to the southeast separates the mine from the old Union Pacific mine No. 2, the other separates it from Union Pacific mine No. 4. The latter fault has been struck at several points, but the displacement has been determined at only one place, where it is 65 feet. Several other small faults and many slickensides are encountered in the eastern part of Union Pacific mine No. 1.

At a point nearly 3,500 feet from the mouth of the main slope a fault was encountered having an upthrow to the west of about 70 feet. Its general direction is northeast by north. The same fault in the main slope of mine No. 5 has a displacement of only 17 feet, and it seems to have died out farther to the northeast. In other words, the displacement of this fault decreases more than 50 feet in a horizontal distance of less than 1,000 feet. The coal bed contains 10 feet of clean coal west of this fault. The slope, which has an average inclination of 10° to 12°, was gradually flattened to half pitch and was so continued until the coal was again entered beyond the fault. There are a few minor faults and a considerable number of slickensides throughout the mine.

Union Pacific Coal Companys mine No. 2. — The Union Pacific Coal Company's mine No. 2, approximately half a mile south of the moutli of No. 1, was opened in 1871 on the same bed as No. 1, and operated until 1883, when it was abandoned because it contained too much water and on account of the numerous faults in this region. Faults of considerable magnitude bound this mine on the north and south. The fault between mines Nos. 1 and 2 has a general southwesterly direction and a maximum downthrow of about 70 feet toward the northeast. Approximately 30 acres of coal was mined. The bed contains some bone and dirty coal in the western and southwestern portions of the workings; however, as the lower entries in mine No. 1, less than a mile to the west, are driven more than

Southern Rock Springs Coal. Field, Wyoming. 263

half a mile farther south than the south end of mine No. 2, the bands of shale do not appear to interfere with mining and are not persistent.

Union Pacific Coal Companys mine No. 4- — Mine No. 4 lies to the northeast of No. 1. The slopes of the two mines are nearly a mile apart and opened on the same bed. The slope of No. 4, approximately half a mile northeast of mine No. 3, was driven parallel to the slope of No. 3 for a distance of 3,500 feet. Nine entries were turned off the slope on the south side and seven on the north. This mine was opened in 1884 and worked until 1895, when it was abandoned, as it ran into dirty coal on the north and all the good coal appeared to be worked out. The slope of No. 4 passes a little to the northeast of the true dip, which is locally about N. 65° W. Consequently the slopes of mines Nos. 1 and 4 diverge at a wide angle.

The coal bed in this mine contains two partings. The upper one is very persistent, though only 1 or 2 inches thick. It is a yellowishwhite fine-grained argillaceous sandstone. The lower parting is the ordinary liighly carbonaceous shale or so-called slate. It is not so persistent as the upper one, although present at many places. It disappears in the southwesterly working and tliickens toward the northeast. These partings are peculiar and well worthy of description. Below the burned zone which marks the outcrop, good coal is mined from both sides of the slope and shows only the ''ellow band about 2i feet from the top. The lower levels ultimately strike bands of shale, at first a great distance from the slope, then nearer to it, until finally the shale shows in the face of the slope itself. The most prominent band is developed about 3 feet from the floor of the bed. Then other bands appear higher up and the yellow band changes to carbonaceous shale and thickens. Finally the lower band changes into sandstone and abruptly thickens by the raising of its upper surface until it replaces the entire upper portion of the bed. So rapidly is the change accomplished that the upper bench disappears within a distance of only a few yards beyond the point where the sandstone first begins. One entry that has been driven for 80 yards beyond this point shows 3 feet of coal on the bottom, continuing with great regularity, but with no sign of the upper portion of the bed ; nor does a drill hole 8 feet deep show other than pure sandstone. At the face of the slope there is 2 feet of bony coal which has to be thrown out in mining, but the sandstone is not present. The entries to the south near the face of the slope pass out of this bony area within a short distance and the bed assumes its normal condition. In this direction all the development, both in this mine and in No. 1, tends to show that there is a very large area of excellent coal. Although the mine had a large supply of coal it was a one-sided mine below 2,500 feet from the surface — that is to say, all of the coal had to come from the southwest side of the mine below

264 Contbibutions To Economic Geology, 1908, Pabt H.

that depth on the slope. As soon as the southwesterly workings of the mine struck the fault that divides it from No. 1 and all the good coal was taken out the mine was abandoned.

Union Pacific Coal Companys mine No. S. — The Union Pacific mine No. 3 was opened in 1873 and continued in operation until 1895, when it was abandoned because of a fire in the mine, which lasted for several years. It is reported that the mine was nearly worked out and for that reason was not reopened. The mine was opened on bed No. 3 and the slope was driven for a distance of about 4,000 feet N. 20® W., or a little northeast of the true dip. Twenty-four entries, twelve on each side, were turned oflF from the main slope and driven north and south for a distance of more than a mile. The face or breast of the mine extends for a distance of 2 J miles, or from mine No. 5, with which it was connected, to the north end of sec. 23, T. 19 N., R. 105 W. Mine No. 3 exposes from 6 feet 6 inches to 7 feet 6 inches of clean homogeneous coal, and in the block of ground between slopes No. 3 and No. 5 the coal preserves the same character. The coal rests upon a bed of fire clay more than 1 foot thick, under which there is a bed of coal about 14 inches thick. Over the large bed there is first a clay shale, then sandstone. On the north side of the slope a band of shalo appears about 2 feet from the floor of the coal. It changes to sandstone farther northeast and there only the bench above it is mined. In some places where the sandstone first appears the upper bench narrows to such an extent that rooms are not turned off, but 200 feet bevond tliis bench widens and affords from 4 feet 6 inches to o feet 0 inches of good coal. As in mine No. 4, this shale zone is far from the slope at the surface and rapidly approaches it with depth, so that it soon reaches the face. In other words, the edge of the bony area runs about halfway between the dip and the strike of the bed. The levels from a point near the face of the slope southwest ward show 7 feet 0 inches of clean coal. The north entries strike a fault that seems to correspond to the one between mines Nos. 1 ami 4. It has a displacement of 8 to 12 feet. Although its course is approxiniaicly north and south, it is very irregular. This indicates a dvin out of the fault toward the north.

Vnion rttcitic Coul Comixnu/s old mine Xo. 5. — Old mine No. 5 of the Union Pacific Coal Company was opened on bed No. 5 in 1879 and was abandoned in 1885, after approximately 20 acres of coal had been mined. The coal was mined through a slope from the surface. As soon as the mine was well opened it was learned that bed No. o too much shale to be of value and th mine was therefore abandoned. It is the only attempt made to open this bed in the Kock Springs tield. A fault was encountered on the north side of this mine that is presumably the same as the one mentioned in the description of mine No. 5 below. The same fault is present in

Southern Rock Springs Coal Field, Wyoming. 265

mine No. 1, which is on a bed 414 feet stratigraphically lower than bed No. 5.

Union Pacific Coal Company's mine No. 5, — The mouth of Union Pacific mine No. 5 is less than half a mile southwest of No. 3, with which it is connected, and is just east of the mouth of old mine No. 5. The nune was opened in 1885, operated until all the good coal was worked out, and then used as a part of No. 3 mine until 1890, when it was abandoned. There is but httle to say regarding mine No. 5 that has not been covered in the description of mine No. 3. Both of these mines were opened on bed No. 3. Mine No. 5 was worked through a shaft, with a slope from the point where it struck coal bed No. 3. The slope was driven down the dip, approximately parallel to the slope of Union Pacific mine No. 1. The shaft of mine No. 5 is approximately 600 feet north and the face of the slope 900 feet north of the No. 1 slope. Twelve entries were turned oflF from the main slope, six toward the south and six toward the north. The north entries were driven only a short distance, as there is another area to the southwest of the mine in which a heavy band of shale appears near the center of the bed. This belt runs nearly at right angles to the stratum of sandstone near the bottom of the bed, as shown in the northerly workings of mine No. 3. A small fault cuts across the slope at the mouth of No. 5 entry. The strike is N. 80° E. and the block on the north side of the fault was moved upward about 6 feet.

Union Pacific Coal Company's mine No. 7. — Union Pacific mine No. 7 was opened in 1888 on coal bed No. 7 and was the first mine operated by this company on this bed. The mine was opened by means of a 1,300-foot entry driven on the strike. From this entry diagonal slopes run to the rise and entries are driven to each side. The entries have been pushed northward and northeastward for a distance of 4 to 5 miles, or nearly to the north township line. One entry extends into sec. 6, T. 19 N., R. 104 W. The entire underground workings of this mine are connected with mines Nos. 8, 9, and 10 in such a way that they are practically all part of one big mine, although they have separate slopes and entries. They are ventilated as if they were one mine and they are all made to drain to the pump of No. 10, which is the lowest on the dip. A fault was encountered near the north quarter comer of sec. 7, T. 19 N., R. 104 W. The bed south of the fault has moved up 12 feet. Several smaller faults and many sUckensides were observed in the mine, but these do not interfere with .

Union Pacific Coal Company's mine No. 8. — Mine No. 8, which is connected with Nos. 7, 9, and 10, was opened in 1889 and is still in active operation. It is worked through a triple-compartment vertical shaft 180 feet deep. The coal is not screened or assorted. A

266 Contributions To Economic Geology, 1908, Pabt Ii.

single-track entry 14,000 feet long connects the lower ends of four single-track slopes with the shaft. Entries are driven on each side of the slopes and rooms are turned off parallel to the slopes.

The greatest pitch in the mine is about 7°, but varies from 5° to 7°. The coal near the shaft is 4 feet 6 inches thick, but farther down in the mine it is 7 or 8 feet thick and it averages from 7 feet 4 inches to 7 feet 7 inches. A layer of soft J;)lack shale 2 feet thick occurs just above the coal all through the mine. About 2 feet below the top of the coal bed, or approximately 5 feet 5 inches above the bottom, there is a thin shale parting which persists throughout the mine. It is in few places more than an inch thick. It keeps a uniform distance from the top of the coal bed, any increase in the thickness of the bed being added to the lower bench. The coal is very clean and needs no assorting after leaving the mine. Considerable pyrite was observed near the shale and the pyrite near the base of the coal occurs in little, thin plates. Below the coal bed there is 6 feet or more of brown shale containing in places a little coal. Below this is a sandstone layer. The roof of the mine is a bluish to chocolate-colored shale locally carrying fossils. AVhere fossils are present the roof is not so good as elsewhere. In mining, a thin layer of coal is left to form the roof, as it is better than the shale, wliich is liable to flake off.

The dip (5° to 7°) remains nearly constant throughout the mine. The strike, which is a little east of north at the shaft, gradually swings toward the west, till at the end of the mine it is a little west of north.

Union Pacific Coal Campanys mine No. 9. — Union Pacific mine No. 9 was opened in 1890. The mouth of this mine lies 200 feet southeast of No. 7. It is the eastern part of the big mine formed by the connection of Nos. 9, 7, 8, and 10, which lie in the order named from eat to west along the north side of Bitter Creek valley. This mine is worked very much like No. 8, except that the main entry is reached by an 800-foot slope instead of a vertical shaft. The main entry is 12,700 feet long, and the coal is brought to it through three slopes driven to the rise. The entries of No. 9 are not driven so far north as those of No. 7, which they parallel, but they have entered the S. i sec. 7, T. 19 N., R. 104 W. The method of work and operation is the same as in mines Nos. 7 and 8.

Union Pacific Coal Company s mine No. 10. — Mine No. 10 was opened by the Union Pacific Coal Company in 1900 and is still in active operation. It is the westernmost member of the big mine represented by Nos. 10, 9, 8, and 7, which produces nearly 1,500,000 tons of coal annually. The mouth of No. 10 mine lies approximately 600 feet west of No. 8 shaft. A rock slope with a grade of 15° reaches the coal at 1,200 feet and extends 1,500 feet in the coal at a 5° dip.

Southern Rock Springs Coal Field, Wyoming. 267

A fault was encountered in this mine near the mouth of the second entry. Its strike is a little east of north, but in going northward it swings toward the west, and where it cuts No. 3 and No. 4 entries the strike is nearly due north. Where the fault cuts No. 5 entry, 900 feet from the slope, it has a displacement of only 7 feet. An area of poor coal was encountered in the NW. i sec. 24, T. 19 N., R. 105 W., as shown by openings in entries Nos. 4, 5, 6, and 7. The main slope ran into dirty coal and was abandoned. Entry No. 7 encountered this zone at 900 feet; entry No. 6 entered it 1,500 feet from the slope and was abandoned; entry No. 5 encountered the poor coal at several places 1 ,600 to 8,000 feet from the slope and is not worked at the present time.

Central Coal and Coke Company s mine No, 2, — The Central Coal and Coke Companys mine No. 2 was- opened in 1888, on bed No. 7. The mouth of the mine lies about IJ miles south of the shaft of the Union Pacific Coal Companys mine No. 8. A slope is driven down the dip approximately 2,700 feet and entries are turned off toward the north and south. Most of the mine workings lie in the north and west halves of sec. 36, T. 19 N., R. 105 W.

In the southern part of the mine the coal is 6 feet 6 inches thick, in the northern part 4 feet 8 inches. xOn the north side a layer of bone from 4 to 8 inches thick is associated with the coal, but it pinches out before reaching the south side. Overlying the coal bed is 3 feet of shale, and on top of this is a 20-foot bed of gray sandstone. Twenty inches below the top of the coal bed is a shale parting three-eighths of an inch thick. A considerable number of slickensides and a few faults were observed in this mine. The largest fault lies in the SW. sec. 36, and cuts the entries approximately at right angles. Farther west the strike changes and the fault passes into sec. 35 with a trend a little south of west.

Sweetwater Camp.

The Sweetwater camp is the southernmost camp in the Rock Springs district. At present only the Central Coal and Coke Company is operating in this camp. This company is working bed No. 7, and has thus far worked four mines — Nos. 1, 3, 4, and 5. Mines Nos. 1, 3, and 4 were practically worked out in 1907. What little coal remains will be taken out through No. 5 slope. All these mines were combined in the fall of 1907 and are considered as part of the Central Coal and Coke Company's mine No. 1. The camp is reached by a spur built up Sweetwater Valley from Blairtown, on the Union Pacific main line.

Central Coal and Coke Company* 8 No. 1 mine. — Mine No. 1 of this company was opened by Mark Hopkins in 1888 at Hopkinsville. Its mouth is a little northeast of the center of sec. 14, T. 18 N., R. 105 W.

268 COirTBIBUTIONS TO ECONOMIC GEOLOGY, 1908, PABT II.

Shortly after the mine was opened it was sold to the Sweetwater Coal Mining Company and the name of the village was changed from Hopkinsville to Sweetwater.

The coal in this mine is from 7 feet to 7 feet 6 inches thick with neither bone nor parting. A stratum of impure clay only a few inches thick immediately underlies the coal and below this there is a firm, massive gray sandstone. Above the coal there is 10 feet of clay shale overlain by a reddish sandstone that is very persistent. The dip in the mine averages from 7° to 8° N. 85° W. A system of joints or slips commonly present in the Rock Springs coal is very prominent in this mine. In many places they part the coal from roof to floor every few feet. They are without doubt closely related genetically with the movements that produced the faults in the coal-bearing rocks. These slips run 5° to 20° south of the dip and are generally inclined toward the south. The faces present every peculiarity of faults, and along many of them there is an actual displacement of 1 to 4 inches. The fissures showing such a displacement usually pass into the roof of the bed, but where no displacement is observed this is not the case.

Central Coal arid Coke Companys mine No, S. — Mine No. 3 of the Central Coal and Coke Company lies in the NW. i sec. 12, T. 18 N., R. 105 W. It is opened by a slope to the main entry, with slopes to the rise. This mine was nearly worked out in 1907 and has since been worked only in order to open mine No. 5, in sec. 11, north of the fault. The coal bed (No. 7) in mine No. 3 is about 5 feet 2i inches thick where it was sampled in slope entry No. 5, but runs from 4 to S feet in the mine. The clay parting is one-fourth inch thick and inches below the top of the coal. The coal is very similar to that mined by the same company in mine No. 4. Twenty feet above bed No. 7 lies another bed from 4 to 12 inches thick, but thus far no attention has been given to this upper bed.

At the back air course of entry No. 5 is a fault with a downthrow of 20 feet on the north side. South of the fault the coal is from 7 to 8 feet thick and north of the fault it is from 4 to 6 feet thick. Many slickensides and minor faults similar to those in mine No. 1 were noticed throughout the mine.

Central Coal and Coke Compani/s mine No. 4- — The Central Coal and Coke Company's mine No. 4 was nearly worked out in the fall of 1907. It lies north of No. 1 and west of No. 3, in the SE. i SE. i sec. 2, T. 18 N., K. 105 W. It was opened on bed No. 7 by a slope of 6° about 1,700 feet long. A fault is present 1,300 feet below the mouth of the slo})e. The coal in this mine is 6 feet 3 inches to 7 feet thick, with a i-inch shale parting 2 feet 3 inches below the top of the

a la HuUtitia 341, p. 27U, tbo coal bod was erroneously reported to be 12 feet thick io thla mine

Southern Rock Springs Coal Field, Wyoming. 269

coal bed. The dip of the bed is about 5® SW. and the strike about N. 5® W. On top of the coal bed lies an 8-foot layer of shale. This is hard, dark, and very fossiliferous. Above the shale is a gray sandstone; in places the dark shale is missing and this sandstone forms the roof of the coal. Below the coal is a massive bed of gray sandstone approximately 20 feet thick. No attempt is made to separate the shale parting from the coal. The mine is dry and only along the fault above mentioned was water observed. In the lower workings in the northwestern part of the mine a small spring was encountered near the fault. Many slickensides and minor faults occur in the mine, the conditions in this respect being very similar to those in mines Nos. 1 and 3. As measured on the parting the displacement ranges from a few tenths of an inch to several feet. The coal usually breaks along these walls or slips, and this breaking facilitates mining. The slickenside planes can be traced readily into the roof, but do not show displacement. Some sulphur balls are present in the coal, but most of the sulphur occurs near the base of the coal bed in the form of lenses. In addition some sulphur is disseminated through the coal.

Central Coal and Coke Companys mine No. 5, — The Central Coal and Coke* Company's mine No. 5 was opened in 1907. It lies north and east of mine No. 1. A new slope was being driven in the fall of 1907. It was the intention of the manager, in order to shorten the haul, to combine all that was left of Nos. 1, 3, and 4 as soon as new entries were connected, about December 1, 1907. The coal in mine No. 5 in dip room No. 2 off back entry No. 5 is 7 feet 9J inches thick. No shale parting occurs in this bed northeast of the workings in mine No. 1. The roof is shale and the floor is gray sandstone, as in mines Nos. 3 and 4. At the fault along the north side of mine No. 1 and south of No. 5 the coal on the north side is 3 feet 3 inches thinner than on the south side of the fault, where it is nearly 8 feet thick. The downthrow amounts to about 20 feet on the north side.

The Central Coal and Coke Company's mines Nos. 1, 3, 4, and 5, although opened separately and spoken of as separate mines, constitute in fact one large mine, resembling in this regard the Union Pacific Coal Company's mines Nos. 7, 8, 9, and 10. All the mines are on bed No. 7, and the necessity of opening separate mines or changing the method of mining is due to the displacements caused by the numerous faults in this locality. As soon as mine No. 1 encountered the big fault on the north the entire workings had to be readjusted. Nearly all of the available coal in Nos. 1, 3, and 4 has been taken out. What remains of these mines and the new workings called *'No. 5" are at present known as parts of Central Coal and Coke Company's No. 1 mine.

270 Contributions To Economic Geology, 1908, Part Ii.

Blairtown Camp.

The Blairtown camp lies about a mile south of Rock Springs, and has been the scene of coal mining for many years. The date of opening of this camp is usually given as 1869, although a few prospects were opened before that year. The Rock Springs Coal Company's mine No. 1, or the old Blair mine, was the first to begin operation and started in 1869. P. J. Quealy reopened this mine on bed No. 1 just north of the fault passing through the northern part of sees. 1 and 2. He also opened a small mine on the same bed south of the fault. These two mines lie south of the Union Pacific Coal Company's mines Nos. 1, 2, and 4 on the same bed, described under ''Rock Springs camp.*' In May, 1907, another mine was opened on bed No. 3, a short distance west of the Rock Springs Coal Company's mine No. 1. Beds Nos. 1 and 3 are the only ones on which mines are operating in the Blairtown camp.

Rock Springs Coal Company s min No. 1, — The Rock Springs Coal Company's mine No. 1 is situated in the NW. NW. sec. 2, T. 18 N., R. 105 W. It is said to have been first opened in 1869. Archibald Blair owned the property and opened the prospect as well as the mine. Work continued for a time and then the mine was shut down. Later the old Blair mine was leased to P. J. Quealy, who worked it for some time. Part of this mine, as well as the'E. J sec. 2, became the property of the Rock Springs Coal Company, which reopened the mine in 1887 and produced 47,300 tons of coal in 1888. It was abandoned in 1903. The old Blair mine was opened on bed No. 1 just north of the fault above described. The original opening, known as the 'Quealy mine or prospect," was opened on the same bed a few feet south of the fault by P. J. Quealy while operating the leased Blair mine. Both mines were worked by the Rock Springs Coal Company. The coal from the Quealy mine was run down an incline and loaded into cars at the Blair mine. When operations at the Blair mine were suspended the Quealy mine was also shut down.

In 1902 Matthew Muir reopened the Quealy mine by driving a new entry near the base of Quealys workings, so as to save haulage. The new entry is a few rods west of the Quealy opening. The mine lies between two faults, one at the north, the other on the south, the distance between them being about 750 feet. The coal has been mined 1,200 feet down tlie dip. This property is at present owned by the Ontral Coal and Coke Company, and the mine is leased to Mattliew Muir, wlio employs two miners. Tlie coal is hauled to the moutli of the mine by liorse, transported by wagon to Rock Springs, and sold locally or shipped with the Central Coal and Coke Company's coal. Practically all the coal taken out of this mine

Southern Bock Spbings Coal Field, Wyoming. 271

used in Rock Springs for domestic purposes. Another opening, known as the ''Young mine/ was made in 1883 on the same bed a short distance to the north by George Young. The mine was worked for a short time by the Excelsior Coal Company and then abandoned because the coal was dirty and pinched out. The coal in the Blair mine is about 1 1 feet thick and in all the upper workings of the mine is perfectly clean. Bands of shale are encountered in the southwestern workings. They occur, however, near the base of the coal and 7 feet of clean coal lies above them. Union Pacific mine No. 2, now abandoned, also showed bony coal on this bed in the western and southwestern portions of its workings. It seems probable that there is here an area or zone containing bands of shale in this part of the bed and that both of these mines encountered it.

Wyoming Coal and CoJce Companys mine, — In April, 1907, the Wyoming Coal and Coke Company opened a mine on bed No. 3 north of the fault described above as passing south of the old Blair mine. The south entries were worked only to the fault. Matthew Muir had previously opened a small mine on this bed a few rods south of the Wyoming opening and a few rods north of the fault contact. He leased the mine from Mr. Blair and worked it for a few years, until he encountered water. The new slope opened by the Wyoming Coal Company was driven down the dip of the coal bed, here about 12®. In September, 1909, the slope was down 1,600 feet. About 730 feet down a fault was encountered, which brings bed No. 1 up on the west into alignment with bed No. 3 east of the fault. Before striking bed No. 1 the slope passed through 90 feet of rock. Bed No. 3 was 4 feet 8 inches thick; bed No. 1 on the other side of the fault was 11 feet thick, mostly clean coal, with a few shale partings in the upper portion. In 1909 the company sunk a double-compartment shaft about 300 feet southeast of the mouth of No. 3 slope. The shaft was sunk 139 feet to a point where it struck bed No. 1. From the base of this shaft an entry was driven to the end of the old slope in Rock Springs Coal Company's mine No. 1, commonly known as the 'Blair mine.'' The Wyoming Coal Company purchased the NW. J sec. 2 from Mr. Blair and will extend and complete the workings of the old Blair mine as soon as the present entry connects with the Blair slope. In September, 1909, there was still 400 feet to open up. About 226 feet from the shaft, or 140 feet west of the end of the Blair slope, a small fault was encountered with the downthrow on the east. This is probably the same as the fault seen at the surface on the hill point just northeast of the mine, with a displacement of about 5 feet. A drill hole was sunk at the base of the shaft through bed No. 7, which was found to be 7 feet 6 inches thick. It is reported that the company intends to sink a shaft to

272 Contributions To Economic Geology, 1908, Pabt Ii.

bed No. 7, possibly to the Van Dyke bed, and to mine all these coals. The coal in bed No. 1 south of the old Blair slope is dirty throughout the lower part, having two or three shale partings nearly a foot thick. The upper 5 feet 6 inches is clean coal. West of the fault bed No. 1 is clean coal and has only a few partings in the upper part. Thus far most of the work has been confined to entries, which have been pushed forward as fast as possible, but little room work being done.

No. 6 CAMP.

No. 6 is the only camp on the west side of the Rock Springs dome where a mine has been opened on a coal bed in the Almond coal group. This camp was opened in 1882 by the Union Pacific Coal Company in sec. 22, T. 19 N., R. 105 W. The mine was known as the Union Pacific Coal Company's No. 6 and is often referred to as old No. 6 mine. The following section shows the condition of the coal bed:

Section of coal bed at old No. 6 mine.

Sandstone, soft yellow. Ft. In.

Shale : 1 6

Coal 1 2

Bone 6

Coal 2 1

Shale 1 6

Coal 1 6

Coal, bony 5

(oal 1 11

Shale 6

Sandpit one, soft, yellov.

Total coal bed 9 1

Ovcrlyinj; the coal is about 18 inches of moderately soft chocolatecolored ypsiferous shale containing numerous fossils, apparently of the same species as those found at other points along the outcrop of the Almond coal group.

The mine was operated imtil 1886 and then abandoned, because the quality of tlie coal was such that it could not compete with the Rock coal. A short prospect was opened on a 12-foot bed of coal west of and a little liiher than No. 6, but no extensive work was done on it.

Interstate Camp.

The Intei-state camp lies about 1 J miles north of No. 6 and is the only camp on the west side of the Kock Sprinrs dome in this district where a mine has opened in a coal bed belonging to the Black Rock coal <i:roup. Tliis mine was opened in April, 1889, at the south center of sec. 10, T. 19 N., K. 105 W. Work was continued for a year and abandoned in 1890 on account of the poor ({uality of the coal, wliich could not be shipped without slacking]:. The small amount of coal that was mined was hauled to market in wagons or to the spur

Southern Rock Springs Coal Field, Wyoming. 273

of the Union Pacific Railroad near old No. 6 mine. The coal is of about the same grade as that in No. 6 mine and would have no better market.

Van Dyke Camp.

The Van Dyke camp lies 2 miles east of Rock Springs and was the first camp where the lower coal beds of the Rock Springs coal group were mined. The Van Dyke mine, opened by Hall & Cotton in 1870, is located in the SW. sec. 30, T. 19 N., R. 104 W. The mme was soon abandoned, but was reopened by the Van Dyke Coal Company in 1888, when it produced approximately 20,280 tons.

The coal bed averages 4 feet in thickness. It shows little variation, being as a rule not less than 3 feet 8 inches nor more than 4 feet 2 inches thick. The roof of the bed is clay, which stands well so long as there is a current of dry air to carry away exuding moisture. Where it is not thus exposed it scales down in thick, heavy slabs. The floor is likewise clay, which is somewhat arenaceous a few feet below the coal. The dip of the bed where measured is from 3i° to 5® nearly due west. The coal is clean, showing no shale partings.

Between the Van Dyke mine and bed No. 7 on an east-west line there do not appear to be any beds of coal large enough to work, but there is a group of thin beds lying nearer the Van Dyke than bed No. 7, which increases in size toward the north. About a mile north of the Van Dyke main entry openings have been made on three of these beds, two of them showing only 2 or 3 feet of coal and the third 4 feet 2 inches of clean and bright-looking coal. Farther north, in sec. 8, T. 19 N., R. 104 W., on the western slope of Baxter Basin, the beds are thicker, so that two of them are at least 6 feet thick, a third about 4 feet, and several others smaller. In this section the Gunn-Quealy Coal Company opened its A and B mines, presumably on the lower and upper Van Dyke coal beds, respectively. Two of the larger coal beds have been opened about three-fourths of a mile farther north and are there nearly 7 feet thick. These beds are 40 feet apart and at least 200 feet lower than bed No. 7, which outcrops at the upper edge of the bluff forming the side of the basin.

The Van Dyke mine was again abandoned in 1895, as the thin coal did not yield enough to pay the expense of operation. Since then the property has passed to the Central Coal and Coke Company, which reopened the mine in the fall of 1909 and made preparations to extend the mine workings to much greater depths.

Gunn Camp.

The Gunn camp lies in sec. 8, T. 19 N., R. 104 W., about 4i miles northeast of Rock Springs, on the western edge of Baxter Basin. At this place P. J. Quealy and George Gunn, representatives of the Gunn- Quealy Coal Company, opened mines in order to develop the two beds

7963**— Bull, 381—10 18

274 Contributions To Economic Geology, 1908, Part Ii.

which have been known throughout this district as the Van Dyke coal beds and which up to that time had been mined in a small way only in the Van Dyke camp, about 3 miles southwest of Gunn. In July, 1907, work was commenced on a spur from the Union Pacific main line near Baxter to the mine, and in September of the same year development of the mine was begun. The first shipment of coal was made in May, 1908.

The Van Dyke coal beds lie near the base of the Rock Springs coal group, and the lower bed, on which mine A is located, is probably the same bed as the Van Dyke, on which the Van Dyke mine was located. The mouths of the mines are about 4i miles northeast of Rock Springs. Mine A is opened on the lower Van Dyke bed and mine B, 40 feet stratigraphically above mine A, is on the upper Van Dyke bed. Regarding the mines at the Gunn camp Superintendent H. E. Lewis makes the following statement:

The coal pitches at this point about 9i° W. 8° S.; the upper bed averages a little more than 6 feet thick. The lower bed runs about 4 feet 9 inches thick, being thicker toward the north. The lower mine, or A, is 400 feet deep, with three entries turned off. The upper mine, or B, is 1,200 feet deep, with eight entries turned to the north and south. The upper mine, B, struck water level at the sixth level, or 900 feet below the surface, yielding about 200 gallons per twenty-four hours.

Other Openings.

Many other prospects and entries have been opened on the Black Rock, Almond, and Rock Springs coal beds in the Rock Springs district. The most important are the Ludvigson mine, in the SW. J NW. i sec. 1, T. 18 N., R. 105 W., on bed No. 7, and the Carleson mine, in the SW. i NW. J sec. 6, T. 18 N., R. 104 W., on one of the coal beds near the base of the Rock Springs coal groiij). Veiy little coal has been taken from these mines, most of it ccmiing from the entries. The Ludvigson mine was opened between two laige faults and occupies the territory between the Central Coal and Coke Company's mine No. 2 at Rock Springs and the same company's mine No. 1 at Sweetwater. Most of the other openings were made primarily for prospecting ])urposes, with no intention of developing mines at those particular ])laces.

Point Of Rocks District.

The Point of Rocks district includes all the coal-bearing beds on the east side of the Rock S])rings dome in the vicinity of Point of Rocks, or that part of the field north of Hallville, which is drained by Ninemilo, Tenmile, and Twelvemile creeks — the area whose natural source of supply and transportation centers around Point of Rocks. Although this was one of the first districts to be opened in the Rock Springs field, very little mining has been done in it. Thus far only one camp, a mile east of Point of Rocks station, has been opened

Southern Rock Springs Coal Field, Wyoming. 275

in the district. The Wyoming Coal and Mining Company, which had a contract to supply coal to the Union Pacific Railroad Company, opened a mine on a coal bed of the Almond coal group at this place as early as 1868. The main drift at this mine was driven northward at right angles to the dip of the beds, which is nearly due east. The mine was in operation until December, 1869, and was then abandoned, owing to the poor quality of the coal, as the same company was obtaining coal of a better grade at Rock Springs. The total production of the mine for that early period was 7,256 tons.

During the summer of 1907 the Rock Springs and Wyoming Coal Company reopened this mine and built a new spur from the main line to it, and in the latter part of the year began shipping coal. In the hill at this place five coal beds occur within a vertical distance of 80 feet. The lowest is approximately 100 feet above the bed of Bitter Creek. The new company opened two beds in 1907. The upper bed is 6 feet 4 inches thick and the lower 5 feet 1 inch thick. In 1908 the lower bed, which had been opened in 1868 and cleaned out in 1907 in preparation for new work, was abandoned owing to the large amount of impurities which make the coal inferior to that of the upper bed. The poor quality of this coal may be due in part to its weathered condition near the face of the old openings, as it is well known that coal of this type deteriorates rapidly when exposed to the air.

The upper bed varies slightly in thickness and was found to be 7 feet tliick at the face of the mine in October, 1908. The yield of this mine in the fall of 1908 averaged 150 to 200 tons a day. There is a large amount of moisture in the coal, so that the company has considerable difficulty in disposing of the slack. At the mine the dip of the bed is about 6 per cent. The main entry, over 1,000 feet in length, is being driven on the level or in places with a little up grade in order to facilitate handling the loaded cars.

Black Buttes District.

The Black Buttes district lies on the east side of the Rock Springs dome and includes all the coal-bearing beds from the Point of Rocks district southward to Black Buttes Creek, or all the territory in this part of the Rock Springs field wliose source of supply and transportation centers about Black Buttes station.

The district was opened in 1868, when the Union Pacific Railroad was built along Bitter Creek valley. Several mining camps have been established, but none of them are very extensive. The mines in one camp are operated on a coal bed near the base of the Black Rock coal group, and those in all the other camps on coal beds in the Black Buttes coal group.

276 Contributions To Economic Geology, 1908, Part Ii.

Black Buttbs Camp.

The first mine in the Black Buttes district was opened in 1868 in the hill east of Black Buttes station. It is commonly known as Morgan's mine and produced considerable coal. The coal, however, was inferior to the Rock Springs coal and the mine was soon abandoned. About 1890 it was reopened and continued in operation until 1893, producing about 50,000 tons. It was then again abandoned, presumably on account of poor markets for coal of that kind. The company worked an upper bed 4 feet thick and the main bed, 15 feet lower, 8 feet thick. The latter supplied most of the coal while the mine was in operation. In the summer of 1907 the mine was filled with water, so that no further investigation could be made.

During the days of the overland stage a small mine was opened just back of the stage station where coal was mined for local use. Another small mine, known as Maxwell's mine, was opened in the SE. i NE. i sec. 9, T. 18 N., R. 100 W., but was abandoned shortly afterward. Nothing further was learned regarding it.

In 1907 the Rock Springs-Gibraltar Coal Company opened a mine about 1 mile southwest of the old Black Buttes mine, on the same coal beds. The upper or principal bed is 6 feet 6 inches thick, and the other, 78 feet below, is 4 feet 6 inches thick. Another bed of good coal 2 feet 2 inches thick, which at present is not prospected, lies 13 feet 8 inches below the second bod. In working the coal the miners go in a short distance and then drift along parallel to the outcrop. A slope on the upper bod is opened down the dip to a depth of 300 feet. The output of this mine in the fall of 1908 was about 200 tons a day.

Hallvule Camp.

The old Hall mine, about 4 milos northwest of Black Buttes station, on the west side of the railroad, was opened in 1868 on the same group of coal bods as those at Black Buttes. Kogarding this mine Clarence King makes the following statement :

There are four seams of coal known to exist upon the claim. The upper one, 4 feet 8 inches in thickness, is near the surface and has never been developed, as tJie coal would be likely to prove of inferior quality. The sei'ond seam is 5 J feet in thickness, and has been worked to extent, funiishing all the coal that has been sent to market fnnu this mine. The third seam, 12 feet below the second and separated it by a stnitum of shale, is 9 feet 8 inches in thickness and proiaises to furnish a coal fully equal in quality to that taken from the one above. No work has been done it further than to prove its existence. The lower seam is not developed but is supixieeii to be about 3 feet in thickness.

Tliis mine was situated just south of a largo fault which carries the bods on tlio south side stnoral milos toward the west. The mine was opened on a largo fault block Wtwoon Hallvillo and Black Buttes,

a I'. S. Cieol. . 4Wh Par., vol. 3, p. 470.

Southerk Hock Springs Coal Field, Wyoming. 277

and the beds are considerably distorted and irregular." The mine was worked for a short time and then abandoned. At present only the ruins of the old camp remain.

In 1906 a mine was opened in a Black Rock coal bed east of the raiboad, in sec. 28, T. 19 N., R. 100 W., by the Sioux City-Rock Springs Mining Company. This mine is south of a large fault which here, as well as at the old Hall mine, carries the beds on the south side several miles to the west. The company soon became involved in litigation, and all development work was abandoned. The mine was opened in a bed of coal 21 feet 10 inches thick by a slope driven down the dip to a depth of 300 feet. The first 100 feet was open-cut work, the remainder under cover. Along the slope about 8 feet of coal was removed, the rest of the bed being left in place.

Other Districts.

Many prospects and small local mines have been opened in various parts of the field (see Pis. XIV and XV) from which coal is taken in small quantities for local ranch use. These mines have not passed the prospect stage and will therefore not be considered at this time. There is no doubt that as future demands increase many new districts will be opened in the Rock Springs field, and that each district will contain several flourishing mining camps.

Economic Considerations.

Mining Operations.

Coal-mining operations in Sweetwater County have so far been conducted chiefly by two companies, the Union Pacific Coal Company and the Central Coal and Coke Company. At present the former operates almost wholly for the purpose of supplying coal to the Union Pacific Railroad. At Rock Springs the Central Coal and Coke Company has been mining coal for commercial markets since 1889. This company operates all the mines at Sweetwater and one mine at Rock Springs. The shipments of coal from other localities in tliis field have been meager and never exceeded a few hundred tons a day. Mines at present are being worked in the vicinity of Gunn, where the Gunn Mining Company is producing from 600 to 1,300 tons a day; at Point of Rocks, where the Rock Springs and Wyoming Coal Company is mining from 150 to 200 tons a day; and at Black Buttes, where the Rook Springs-Gibraltar Coal Company is mining about 200 tons a clay. Outside of the Rock Springs and Black Buttes districts development has been confined to a sUght amount of prospecting and to the opening of a few small mines from wliich to supply the local ranches.

aSee BuU. U. S. Oeol. Survey No. 341, 1909, PI. XIV, p. 258.

278 CONTBIBUTIONB TO BCOKOMIC OEOLOGY, 1906, PAST n.

No doubt as future development work progresses most if not all of the mining in this jKeld will be done by carrying slopes from the outcrop, much in the same way as at present. In places it may be found advantageous to sink shafts along the valleys some distance back from the outcrop where the overlying Tertiary beds have been removed. The room-and-pillar system prevails throughout the field As a rule the pillars are not pulled at present. Mining is genera% done by shooting off the solid face of the bed, but undercutting hand and machine is employed in some of the mines. There is comparatively little gas, and accidents from this cause are relatively rare.

Futurb Development.

When new mines are to be opened in this field, whether in those districts where mines are already in active operation or in new districts far removed from any active mines or rsdlroad stations, it will be necessary to consider carefully such factors as transportation, timber, and water supply, as well as the number, thicbiess, and pe sistence of coal beds, as all these items play important parts in the economic development of a new mine or district.

The most accessible routes for railroad transportation, and those of easiest grade, lie along the larger valleys or main drainage tributaries of Bitter Creek, namely, Little Bitter, Salt Wells, Black Buttes, and Killpecker creeks and their tributaries. Spur tracks built along any of these valleys will become feeders to the main line along Bitter Creek and afford an easy means of transportation, as gravity can be utilized in part in running the loaded coal cars from the mining camp or district to the nearest point on the main line.

In most of the mines thus far developed the roof and floor of the coal beds are firm and give little trouble in mining. It is necessary, however, to use timbers in parts of the mines. All props used in the mines must be shipped in, as thre is very little timber in the region. Besides the few pines on Steamboat Mountain, in Pine Canyon, on Pine Buttes, and on Little Mountain, the only available timber is the juniper or scrub cedar used for posts, corrals, and fuel. The nearest sources of timber supply for mine use are (1) the Uinta National Forest, south of the field; (2) the Teton National Forest, in northern Uinta County, whence the timber could be floated down Hams Fort: to Kemmerer or Granger and then shipped eastward by rail; (3) the mountain ranges on the east, including the Sierra Madre and the Ferris and Green Mountains; (4) the Wind River Mountains on the north, whence the timber could be hauled direct to the mines in the northern part of the field or could be floated down Green River and its tributaries to the town of Green River, and thence shipped eastward over the Union Pacific Railroad.

SOUTHERN ROCK SPRINGS COAL FIELD, WYOMING. 7d

This entire region lies in the Red Desert of Wyoming. The only water available is that of Bitter Creek and a few small streams in the southwestern part of the field. The water of Bitter Creek is scanty in amount and not fit for domestic use. The few isolated springs that are scattered over the region are located for the most part along fault Unes or along the contact of the lower shale of the Green River formation with the underlying formation. They furnish, as a rule, only a small quantity of water and can not be depended on to supply a mining camp. At Rock Springs water from Bitter Creek and water pumped from the mines is used to some extent for stock, but all water for domestic or household purposes is pumped from Green River. For the other mining camps in this district water for domestic purposes is shipped in large tanks by rail from Green River or Point of Rocks. In addition to the water shipped in, the water from small springs that rise along the faults in these localities is used by the miners at Superior and Point of Rocks, but this supply is not sufficient for a mining camp.

It appears, from well records and flowing wells at Rock Springs,

Superior, Bitter Creek, and other points along the Union Pacific

Railroad, that water can be obtained in almost any part of the Rock

Springs field, outside of the Baxter Basin, which lies in the central

part of the dome, by drilling to considerable depths. Whether the

supply in all places will be large enough to meet the full demand of a

mining camp or sufficient for irrigation or other agricultural needs

can be determined only by careful and systematic drilling. In

many parts of the field, particularly in the Great Divide Basin and

other points along the east side of the dome, water may be obtained

by drilling to relatively shallow depths, say several hundred feet.

This water is likely to be highly alkaline and not good for domestic

use.

Markets.

This field is situated about midway between the coal fields of Uinta County in southwestern Wyoming and those of Carbon County in south-central Wyoming. The coal from the Rock Springs field has about the same markets as that at present shipped from the Kemmerer and Ilanna fields. Coal from these two fields has been carried eastward as far as Omaha, where it comes into competition with the coals of Iowa and Missouri; southward as far as Denver, where it is marketed with the Colorado coals; northward to the Black Hills, where it competes with the Sheridan and Cambria coals; and westward as far as the Pacific coast. During 1907 the demand of the western markets became so great that eastward shipments from Rock Springs were entirely abandoned and all the commercial coal produced was sent westward. wSo far as can be predicted the local

280 Contributions To Economic Geology, 1908, Part H.

market for the coal will be slight. Outside of Rock Springs and the villages and towns lying to the east and west along the Union Pacifie Railroad and Oregon Short Line, with their various connecting liiMB and centers of industry, the use of the coal in this field will be CCMH fined to that needed by a few scattering ranches and in the devel ment of the mineral resources of the surrounding mountains, doubt a large part of the coal will be used by the railroad comp for fuel. Up to the present time only a small amount of the R Springs coal has found its way into commercial channels. Besi the present market furnished by the Union Pacific, Southern P and other western railroads using this coal for locomotive t there is a ready market in many cities in the Rocky Mountain Pacific States. The good quality of the coal and its nearness to great smelting and sugar -refining industries in Salt Lake v Snake River valley. Anaconda, and Butte should command a market. At present nearly all of the commercial Rock Springs goes west, the greater part of it to wSalt Lake City, Utah.

Available Coal.

In computing the amount of available coal in the southern part the Rock Springs field, mapped in the summer of 1908 and disc in this report, only those coal beds which are 2 feet 6 inches or m thick have been taken into consideration, although it is well kno' that bituminous coal beds 2 feet and less in thickness are being mined at present in Missouri, Arkansas, and many other States. average thickness of the beds may be obtained from the representativtS sections given in the discussion of the four coal groups. It is assumed, that the average thickness of the coal bed as computed from measurements made along the outcrop will hold equally well for tte bed down the dip. All tlie coal in the Rock Springs coal belongs to the ])ituniin()us class and that of the Almond, Black But Knobs-Cherokee, and Black Rock coal groups to the low-j bituminous and high-grade subbituminous classes. The s gravity of these coals is about 1.3. A bed with a specific gravity 1.3 and 1 foot thick contains about 1,132,500 sliort tons persquaid mile, or 1,770 short tons per acre. Using this factor in the calculai tion and taking all coal beds 2 feet 6 inches or more in thickness Ut a depth of 1,500 feet below the surface, or about 200 feet less that the deepest mine worked at ])resent at Rock Springs, we obtain foif the Rock 8])rings field the following gross tonnage: i

i.

T

Southern Rock Springs Coal Field, Wyoming.

Estimated gross tonnage of coal to a depth of 1500 feet in the Rock Springs coalfield,

Wyoming.

[Short tons.]

Coal group.

Southern part ' Northern part , of field. I offieId.a I Total.

Rock Springs ' 3. 032, 100, 000

Almond 3, 818, 200. 000

Black Buttes 3, 000. 000. 000

Knobs-Cherokee 2.000,000.000

Black Kock 8,590.950,000

4.843.000.000 3,110,783.000 2,790,450.000 6,000,000,000 35,570,640.000

7,875,100.000 6,928.983,000 5,790.450.000 8.000.000,000 44.167,590,000

20.441,250,000 52,320,873,000

72,762,123.000

aSchultz, A. U., Bull. IJ. S. Oeol. Survey No. 341, 1909, p. 282.

If the same factors are used but the computation is extended from the surface to a depth of 3,000 feet, or to the lowest limit of coal at present considered by the Geological Survey as workable, the estimated gross tonnage for these coal groups would be approximately twice that given in the above table.

It should be borne in mind that the amounts given above are merely estimates and that the total may vary from these figures by 25 to 50 per cent. The factors for computing the amount of coal present in the Knobs-Cherokee coal group are much more uncertain than those for the other groups, as it is not known where the base and top of these beds lie and how thick or numerous the coal beds are where they are under cover in the Rock Springs field. The tonnage given for this group is therefore merely a guess, based on what is known regarding the group west of the Rawlins dome and the general structural relations of the coal groups in the Rock Springs field.

WEATHERING OF COAL IN THE ARID REGION OF THE GREEN RIVER BASIN, SWEETWATER COUNTY, WYOMING.

By Alfred R. Schultz.

Introduction.

Coal beds in arid as well as in moist climates show considerable deterioration along the outcrop, and this deterioration in many places extends to the base of the belt of weathering or well down into it. The belt of weathering, from a geologists point of view, is the surficial belt extending from the surface of the earth to the level of ground water. In this belt all the important reactions characteristic of the zone of katamorphism, namely, oxidation, carbonation, hydration, and solution, exert their maximum activity. The zone of katamorphism is the zone in which alterations of rocks result in the production of simple compounds from more complex ones. This zone extends from the surface of the earth to a depth of 10,000 meters, and is divisible into two belts — an upper belt of weathering and a lower belt of cementation -the two being delimited by the level of ground water. As the groimd-water level in arid regions lies at considerably greater depths below the surface than in well-watered regions, it is but natural to suppose that the belt of weathering extends to proportionately greater (depths in dry than in moist climates. It would then follow that the deterioration of coal should extend farther the surface in arid regions than in regions where the top of the water lies only a few feet below the surface of the ground. That the deterioration of the coal does not always extend to the bottom of the belt of weathering, as above defined, or even to a considerable depth into this is a fact not well known. In order to ascertain to what (xtent and depth tiie coal beds in the arid regions have been altered, some time was given to a study of the phenomena of weathering in the course of the geologic and stratigraphic investigation of the coal beds in the Rock Springs field, which range in age from lower Montana (Cretaceous) to Wasatch (Tertiary). A large number of coal samples were collected from both above and below the ground-water table, and show to what extent the coal has been altered. All samples except those taken from active oper-

o Van Hise, C. R., A treatise on Mon. V. S. (leol. Survey, vol. 47, 1904, p. It50.

Weathering Of Coal. In Green River Basin, Wyoming. 283

ating mines came from a point in the bed above the top of the groundwater level. In the summer of 1907, when the northern half of the Rock Springs coal field was studied, 59 samples of coal were collected from various places in operating mines, abandoned prospects, and surface diggings. In 1908, when the southern half of the field was studied, 26 samples of coal were collected from various points, making a total of 85 samples collected and analyzed. Of these 45 Were collected from coal beds in the Rock Springs group, 20 from coal beds in the Almond group, 10 from coal beds in the Black Buttes group, and 10 from coal beds in the Black Rock group."

Considered with regard to physical as well as chemical properties, the coals occurring in these four groups fall into two classes — bituminous and subbituminous. The bituminous class includes all the high-grade coal of the Rock Springs group; the subbituminous class all the coal of the Almond, Black Buttes, and Black Rock groups. The difference between these two classes is physical as well as chemical. The Rock Springs coal usually has a lower percentage of water, remains firm and compact on exposure to air, and stands shipping well without breaking down. The coals from the three overlying groups, although from different horizons and of different ages, have essentially the same physical properties and bear a regional resemblance to one another. On exposure to the sun and open air they alter very rapidly, lose their bright luster, air slake, and break down into irregular blocks or powder. Cracks usually form along the bedding planes and somewhat irregularly in other directions. The coal does not stand shipping without breaking down or slaking, unless it is kept from the sun and circulating air while in transit. It may be stocked without slaking if kept from the sun and air. Chemical analyses of the samples taken from the coal beds of the four groups under approximately the same conditions seem to indicate that there is very little difference between the coals of the upper three groups, but that there is a marked difference between the coals of the two classes above mentioned when reduced to a pure-coal (moisture and ash free) basis. The unaltered Rock Springs coal averages approximately 600 British thermal units higher than the coals in the three overlying groups. It is probable that the former has undergone a more complete devolatilization, deoxygenation, and concentration, and does not assimilate oxygen so rapidly on exposure to the air as the other coals. The hydrocarbon compounds represented by the Rock Springs coal appear to be much more stable under atmospheric conditions than those represented by the higher coals.

Oxygenation, or weathering, along the outcrop of a coal bed manifested itself very strikingly as the examination progressed. UnUke

aTh6 straUgraphlc relationship of these coal groups U expVamcd ou '£22r-*2I\.

284 CONTBIBUTIONS TO ECONOMIC OEOLOGY, 1908, PAHl 11.

the difference in physical characteristics, this alteration seems to be much the same in the two classes. It is clearly evident that along the outcrop of a coal bed and down the dip at least three zones may be recognized — those of surface weathering, underground weathering, and unaltered coal.

Zone Of Surface Weathering.

From Work along the outcrop and samples collected from surface diggings and shallow prospects it is apparent that there is a belt of weathering near the surface in which all the coals are affected in much thei same way. The good unaltered coal can not be reached until this weathered zone is removed. The chemical composition aijd the physical properties of the coal from this zone clearly show the altered and weathered condition. Samples taken from surface prospects and placed in air-tight cans soon lose their bright luster, the surface in some cases becoming covered with a velvety brown coating which no doubt is due to the alteration of the weathered coal. Evidence of the effects of exposure is seen in the H: O and VC: C ratios, as well as in the calorific deficiencies. Oxidation and decomposition in the belt of weathering soon alter the unstable chemical compounds of the coal so that it loses all traces of its original physical characteristics and the calorific values in an air-dried sample fall off one-fourth to one-half from those of the unweathered coal. Analysis of a sample taken from this belt of weathering affords an uncertain criterion for determining the value of the coal except in so far as it indicates the approximate amounts of sulphur and ash. The belt of surface weathering ranges in depth from 10 to 50 feet.

Zone Of Underground Weathering.

Besides the alteration observed in the belt of surface weathering similar phenomena were observed at much greater depths along the walls of more extensive prospects, slopes, entries, and rooms of mines, where the coal has been exposed to the air for a long period of time.

Oxygenation of the coal due to similar conditions was observed in many of the larger prospects, shallow mines, and drifts in the Hock Springs coal group. Many of these prospects were opened for 40, 100, or 150 feet and driven at the time of opening some distance back into unaltered coal, so that all of the deterioration now observed has occurred since their abandonment. Similar conditions were found in a shallow mine opened by Mr. Kappes in the SE. SW. J sec. 14, T. 17 N., R. 105 W., and in the old Union Pacific mine No. 5 at Rock Springs. The same conditions were found in the three coal groups overlying the Rock Springs group. The chemical and physical results of weathering are not so apparent in these higher coals as in the Rock Springs coal, owing to the lack of large mines on the higher coal beds

Weathebing Of Coal In Green River Basin, Wyoming. 285

and to the smaller number of samples collected. Some of the best examples of these higher coals showing oxygenation as the result of exposure to air for a long time in mines of considerable depth come from the Rock Springs and Wyoming Coal Company's mine at Point of Rocks and from the old Union Pacific mine No. 6 at Rock Springs. Both of these mines were operated on beds in the Almond coal group and were worked for some time. The same phenomena were observed in the old Black Buttes mine at Black Buttes,* opened on the Black Buttes beds and also on prospects driven into the unaltered coal to depths of 90 and 190 feet.

Oxygenation along the drift, prospect, and mine walls has not altered the coal so completely as in the belt of surface weathering. The coal along the faces of these underground openings where exposed to the air for a long period of time gradually assimilates oxygen, which it takes into combination, forming new hydrocarbon compounds from those present in the unstable equilibrium of normal coal as it lies in the coal bed. This assimilation of oxygen causes the coal to slake and its physical properties to change. On close examination it clearly shows deterioration ; it has lost its bright luster and the smooth, firm surface of fresh coal and shows a decided calorific deficiency. Although the coal obtained from the faces of these old openings may seem firm and little altered, it seldom shows as good chemical results as samples obtained from working faces, and for this reason the analyses of many of the samples from deep prospects, old abandoned mines, and small country banks should not be taken as indicating the real merits of the coal. On the other hand, the analyses of such samples seldom show as poor results as those of coals taken from surface prospects or country banks in the belt of weathering. The following table shows the chemical composition of the Rock Springs coal in the three stages of weathering and the alteration of the coal from its nonweathered stage to its highly oxidized stage in the zone of surface weathering:

Summary of analyses of Rock Springs coal from zones of surface weathering underground

weathering f and unaltered coal, c

Zone Of Surface Weathering.

Volatile matter.

a

b

Q

! Minimum Maximum Average

Ash.

►

"3

r

Go

Q

a See Bull. U. S. Oeol. Survey No. 341, 1909, pp. 270, 277; also p. 272 of this bulletin.

b See Bull. No. 341, p. 276.

For complete analyses see Bull. U. S. Geol. Survey No. 341, pp. Tlin..

286 Contbibutions To Economic Geology, 1908, Pabt Ii.

Summary of analiiset of Rock Springs coal from zonta of turf use wtalhering, undergrouTid weathering, and unaltered coal — ContiQued.

ZONE OF aUBPACB W BATHE RlNG-ConUnunl.

IMEulmum.. tlulmum.. Average

'Veea

Calo

T

?

%

£

k

£

Si (.7

Mi1

,1Kw

!.Mk

Ssm

t,4M

7.Sji

3.0M

FIxfd catbtm. Ash,

33,St ' 33.33 fl.m

"

I r,4

4.se

S.M

n.i7 I Gs'.ia ' 6s.aT i.it

-41 ' 1.H

..as 1.31

Minliiiiim J...X . .>l.\. UOp 4,n 4.8W S.r,n8 , .'lSUR ' R.m ' .f.fiOS 10,094 i 10.B15

11 {Majlmimi x..-n i\.ai *.sa I (i,.-,7S 7.a33 -.4.v; ii,:Oi II.SM 13 018 13 420

WEATHERING Or COAL IN GKEEN HIVER BASIN, WYOMING. 287

mtmued.

Zone Of Unaltered Coal,

VWU.m.,t.r

Ad..

pie.

riM

31. S2 33.39

1

ilflu

S.Iu

si.oi as.eo

4B.Ti

u.os

t.M

4.K1

Sulphur.

rjU'bon.

Nitrogen,

berot

t

1 on

1 Is

an

l.iS

l.U

plw.

l!

infifl ifl w

1J16

.™

7S71

in nil

11 illi

13 Sw

"

The above table shows the range and the average chemical composition of the samples of Rock Springs coal obtained in 1907, The following table gives the average of all analyses of samples of each group of coals obtained in the Rock Springs field in 1907-8 and is here given for the purpose of comparison:

20NE OF SURFACE WEATHEKINa.

rillmslo iinolysls.

Cwl pToup. |-3,

h

t

B

ii|

niaok Rock...

.VJmond 1 ft BSD

Rwk Spring.. s IftW

S8.t

E

4! 86

3&Z3

4, Ml

8.fl23:IO,g8S

288 CONTBIBUTIONS TO ECONOMIC aEOLOGT,' 1908, PAST H.

Zone Of Underground Weathering.

r

!

rroilmale SDalyiTs. UlUmaU knulriu.

It

Jj

'i

1

ji

2

II in

ZONE or UNALTERED CO

Al.

Btock Rook

Rock Springs .

Zone Of Unaltered Coal.

The coal samples collected in 1907 clearly indicated that the phenomena of.weathering are not confined to outcrops or shallow prospects, but extend back considerable distances, even several hundred feet, or to water level, in large mines as well as in shallow mines, country banks, and drifts. A large number of these samples show to what extent underground weatliering or oxygenation has been effective along mine openings, but practically no samples were collected to sliow how far below the surface in the belt of weathering the coal was altered. For this reason coal samples were collected in the summer of 1908 from three of the four coal groups in the Rock Springs field to ascertain if possible to what depth the weathered belt extends below the surface where the coal has not previously been open and exposed to the air. In making these tests it was considered best to collect samples from some of the new mines recently opened, as they offered the best to sample fresh surfaces of coal from the outcrop down to the lowest depths of the workings. New mines were opened in 1907 and 1908 on the Rock Springs coal group by the Gunn-Qupjily Coai Company at Gunn, on the Almond coal group by the Rock Springs and Wyoming Coal Company east of Point of Rocks, and on the Black Buttes coal group by the Rock Springs-Gibraltar Coal Com|)any southwest of Black Buttes. At eaeli of these localities a number of samples were taken, and the results of the analyses are given below. It was not considei-ed necessary to take samples at the surface in t lie vicinity of the mines, as a sufficient number of analyses of samples collected tiie previous year showed the conditions in shallow or surface jirospects at or near the surface.

Weathebinq Of Coal In Greek Bivee Basin, Wyohinq. 289

Coals Of The Rock Springs Group.

In the following table are the results of analyses of samples of the Rock Springs coal obtained at Gunn:

Analifta" of n

[Samples taken In

il/rom Ike Rock Spring* coal group, thawing the effect of weathering a various depths below the surface.

in-tjutsly ininrs, finn. V

F. U, Stonloa.cl

s.

nple laken.

frgslnia

onalyala.

Ifili.

Utat value.

gi

!;

,i

§

Sb

cd

Tow

B

Id

31.W

s.n

S.

1.0*

\V,

Hbo

Hi

4! 71

84.U

.403.' 41.M

as J:"

tl

7:841

12. Bo*

slut

3S.S3

l.TS

4,21

t.M

l.

1.M

T.B81

B

4.90' U.W

l.

1Z.M IS.Tll M.M

I.Is

Tim

14.U

U.Bos

Bbu

B

sr

t.40 lT.n 31.(N

tT.Mi 3.M

1.U

Ss

fi.su

M.M

7,811

or eacb sampLf , arrBDged u foUowg

it received, alrdried, dry coal, pure cotl

The results of analyses of Rock Springs coal taken from surface prospects in the belt of weathering are given in Bulletin 341, page 271, Noa. 5812, 5372, 5371, 5376, 5814, 5809, 5813, and 7090. Analyses of coals in this group showing the various stages of underground weathering as a result of exposure to air appear in Bulletin 341, pages 270 and 271, Nos. 5694, 5696, 5698, 5697, 6043, 5370, 5369, 5368,5357, 5373, 5699; and in the present report, page 243, fo. 6791.

Analyses of good unaltered coal obtained near the surface in small country mines are Nos. 6796 and 6799 of this report (p. 242). No. 6796 was collected from the Mtllor mine, in the NW. i NW. i sec. 24, 7963°— Bull. 381—10 19

290 Contributions To Economic Geology, 1908, Part H-.

T. 17 N., R. 105 W., and No. 6799 from the Kent mine, in the NE. NE. i sec. 14, T. 17 N., R. 105 W. In both of these mines the coal has been exposed for some time, but every winter fresh coal is taken out for ranch use, so that it was possible to get unaltered coal from the working face back only 40 and 75 feet, respectively, from the mouth of the mine.

A comparative study of the analyses of the Rock Springs coal sampled at various places and depths in the Rock Springs, Sweetwater, Blairtown, Gunn, and Superior mines shows that there is a very small range in the percentages of the constituents. This indicates that the unaltered coal is remarkably uniform and bears a regional resemblance in the various mines.

Range in percentages of constitiLents and heat values of Rock Springs coaly as shown by analyses of air-dried samples from the mines at Rock Springs Sweetwater Bhirtovm, Gunny and Superior. a

Moisture 5. 51- 10. 85

Volatile matter 33. 35- 39. 66

Fixed carbon 49. 16- 55. 25

ABh 1.51- 9.30

Sulphur 77- 1.38

Hydrogen 5.22- 5.79

Carbon 64. 17- 73. 51

Nitrogen 1. 15- 1. 57

Oxygen 16. 55- 22. 91

British thermal units 11, 435-13, 158

The twenty-live iin weathered samples collected give no indication that the coal improves in deptli or that the weathered zone extends very far below the surface of the ground, or, as often supposed, to the top of the around-water level. Samples were collect-ed near the top of the unaltered coal, approximately 50 feet below the surface, and at various other places throu<]:hout the mines to a depth of about 2,000 feet below the surface, that of No. 5358, sampled in entr No. 51 of the Union Pacific mine No. 1 at Rock Spring. Of all the mine samples collected the one showing the highest calorific value in the air-dried state is No. 0772, from the Wyoming Coal and Coke mine at Blairtown, taken 90 feet below the surface near the end of the second entry south, about 400 feet southwest of the slope opening on bed No. 3. This sam})le gives 13,158 British thermal units when air dried and heads the list of samples for dry coal with 13,811 British thermal units. On a pure-coal basis only six of the 25 samples show calorific values greater than 14,000 British thermal units. Of these six, four have higher values than sample No. 6772 and all come from shallow or very moderate depths in the mines. The order of these six samples is as follows:

a For complete analyses see Bull. U. S. Geol. Survey No. 341, 1909, p. 270 ; all analyses oa the page cited, except Nos. 6094 aiU ot''9i", represent mine samples.

WBATHEBINQ OF COAL IN OBEEN BITER BASIN, WYOMING. 291 Calorific vahut of pure ooal, tampUtfrom Rod Springt eool group.

5926 14,272

5928 14,162

5366 14,119

5785 14,114

8772 14,069

. 14, Oe

From the table on page 2Sd it will be seen that the weathered coal zone does not reach a depth of 56 feet below the surface but extends to a depth greater than 24 feet, the division line at the Gunn-Quealy mine lying somewhere between these two limits. It is evident also that the coal below the belt of weathering does not improve in quality with increasing depth. On a pure-coal basis the unaltered Rock Springs coal has a calorific efliciency, in round numbers, of 13,600 to 14,300 British thermal units.

Coals Of The Almond Grodp.

The results on the Almond coals are presented below. Analyiti

( takro to

he R

".V

Point of Rocks, Wyo., sec. a

mist to charge.J

VlltouU inalyals.

I, T. W N., R.

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.!71,

292 Contributions To Economic Geology, 1908, Part U.

The results of the analyses of the Almond coal taken from surface prospects in the belt of weathermg are given in Bulletin 341, page 272, Nos. 5950, 5597, 5599, 5348, 5349, and 5350.

Exceptionally good illustrations of underground weathering or oxygenation are given in the Rock Springs and Wyoming mine at Point of Rocks and in the old No. 6 mine at Rock Springs. The mine east of Point of Rocks was opened in 1868 and operated to December, 1869, about 7,256 tons of coal being taken out. From that date to 1907 the mine was not worked. Samples Nos. 5351 and 5352 (Bulletin 341, pp. 271, 272) were collected from the mine in 1907, while the old mine was being cleaned out. On a comparison of the analyses of these two samples with those of the last three in the above table the altered condition of the coal represented by the former will be apparent. Sample No. 5351 was taken from the upper bed at the end of a fresh unfinished crosscut about 20 feet from the old drift opened in 1868-69, 103 feet below the surface and 227 feet from the mouth of the mine. Sample No. 5352 was taken from the lower bed about 70 feet below the upper bed, at the end of an old drift 575 feet from the mouth of the mine.

Old No. 6 mine at Rock Springs, opened on a coal bed of the Almond group in 1882, continued in operation until 1886 and was then abandoned. Analyses No. 6042 (Bulletin 341, p. 271) and No. 6773 (p. 243 of the present report) show the same amount of oxygenation due to exposure to the air. Both of these samples were collected from the main slope approximately 300 feet from the mouth of the mine. Similar results are indicated in samples Nos. 5804, 5353, and 5347 (Bulletin 341, pp. 271, 272) and in Nos. 6797, 7095, 6775, and 7088 (p. 243 of this volume). The above table shows that back from the old mine openings the weathered coal zone does not extend to a depth of more than 100 feet below the surface. How much less the depth is can not be told from the samples here collected, as they wore taken along the old entries. The table also shows that on a pure-coal basis the heat value of the unaltered Almond coal approximates 13,000 British thermal units.

WEATHEBINO OF COAL IN OREEN BIVEB BABIN, WYOMING. 293 COALS OF THE BLACK BUTTES GROUP. In the subjoined table are the results for the Black Buttes coal.

ISsmplalakfDlii tlMRoclcSprliies-aibnltaraiMliiiEas, BlBClc Butlcs,Wya,,Mc. 30, T. ISN., R. lOOn

SampU taken.

J

Proilmute analysis.

Beol vBlM.

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Four analfwa ore given for each aample, arran) as IqIIows: As thc Ived, slr-diltxl, dry coal, pun dub] (moiitiin and uh tnr). fr7S (t btlov upper bed.

N'o samples of coal for analysis were collected from surface pros* pects on the Black Buttes beds. The conditions here are mucli the same as those for the Almond coab. From the above table it may be seen that the zone of surface weathering at this mine extends approximately 100 feet down the slope and is about the same in the lower and the upper bed, although the lower bed lies 78 feet stratigraphically below the upper bed.

Slight weathering was observed in samjdes Xos. 5951 and 5810, collected from the ends of prospects open 90 and 1 90 feet, respectively; also tn sample No. 5952, from the old abandoned Black Buttes mine aoutheaat of Black Buttes station, collected 250 feet down the eatv

294 Contributiokb To Economic Geology, 1908, Pabt H.

from the mouth <if the mine and 10 feet ahove water level. Complete analyses of these three samples are given in the following table:

u entries and protptet piu. [F. U. euoton. cbembt In cbirge.]

J

Rtatviliw.

?

It

WiO

Pro-

Iw

3,ro

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ilM

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mn

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M

tiM

4. Ib

li.n

10 Ji

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tM

iiM

M.Os

Is

a,is8

Ii, Oh

s Four snalyses are eivp

intple, arranged as fo

Isreodved, air-, dry coal, piminl

From the finaly.ses given above it appears that the weathered zone of the Black Biitles coal extends approximately 100 feet down the dip of tlic beds and 40 feet below the surface. The calorific values of unaltered air-dried coal are between 1 1 ,500 and 12,000 British thermal units; on a basis of pure coal the values approach 13,000 British thermal units.

Coals Of The Black Rock Group.

No larj;e mines liave been opened on the Black Rock beds, but there are several small country mines fi-om which a small amount of coal is taken annually for local ranch use, so that it is possible to get good samples of unaltered coal. Thi" results of analyses of Black Hock coal taken fnmi surface )irospecfs in the belt of weathering are given in Bulletin .341, page 272, Nos. .537.') and .5367. Both of these samples give in the ealdnineter approximately oue-half the efficiency of the unallereil coal sampled in tlie small country mines.

Two illustrations of partial weathering and oxygenation are afforded by samples No. .1374 (Bulletin 341, p. 272) and No. C771 (p. 245 of the present report). All other of Black Rock coal were taken from freshly cut faces of small mines that bad passed through the weathered zone and furnished good samples of unaltered coal As ull these samples were taken at distances from 30 to 150 feet from

Weathering Op Coal In Green River Basin, Wyoming. 295

the mouth of the mine it shows that the belt of weathering does not extend very far below the surface. The heat values as shown by samples Nos. 6794, 6774, and 6795, page 245 of this report, and Nos. 5930, 5803, and 5802, page 272 of Bulletin 341, may not be so high as those of the coal taken from greater depths. From the regularity here shown it appears that most if not all of these samples were obtained near or below the lower limit of the weathered zone. The calorific value of unaltered air-dried coal lies between 11,000 and 11,650 British thermal units; on the basis of pure coal it exceeds 13,000 British thermal units.

Conclusions.

It was not considered advisable in this preliminary paper to take up the results of weathering observed by other men in different localities under somewhat different conditions, or to refer to published articles on the weathering of coal. This was left for a fuller discussion of the subject of weathering to be taken up at some future time. In pre- 3enting the foregoing observations on the weathering of coal the factors involved are restricted entirely to those present in the Rock Springs field, and the following conclusions are therefore based on these local data.

The results obtained in the Rock Springs field indicate that so far as coal decomposition or deterioration is concerned the belt of weathering in arid regions may be divided into two members. Coal in the lower member of the belt apparently shows no greater effect of weathering or deterioration than the coal below the level of ground water, but coal in the upper member, or in the surficial belt of weathering, shows remarkable deterioration and decomposition. The protection of the coal above the level of ground water in the lower member of the belt of weathering may in part be accounted for by the accompanying beds of clay and shale, wliich tend to shut out the oxj'gen and free circulation almost as completely as the ground water.

On comparison of averages in the table of analyses of Rock Springs coal showing the three stages of alteration it will be seen that the moisture and oxygen are greatly in excess in the surficial belt of weathering and that tlie fixed carbon and carbon both show a corresponding deficiency, or a loss of approximately 20 per cent from the carbon content in the unaltered mine samples. Volatile matter, ash, sulphur, hydrogen, and nitrogen are fairly imiform in the three stages. There is, however, a sUght increase in the ash content in the weathered belt and a decrease in the sulphur content, which indicates that some of the iron sulphide in the coal has been changed to iron oxide. This view is further supported by the iron stain or oxide seen on the face of the coal in the air-slaked or weathered stage. The sulphur, probably combined hydrogen, is taken into solution in the underground water and carried off as hydrogen sulphide.

296 Contributions To Economic Geology, 1908, Part Ii.

The values for calories and British thermal units show that the factors of weathering are negligible in the Rock Springs coal in the Gunn B mine at a point 80 feet down the slope, or 12 feet vertically below the opening of the mine, where the coal has a cover of 56 feet. On an ash and moisture free basis the unweathered coal shows over 13,700 British thermal units, the average for the 25 unweathered Rock Springs coal samples being 13,875 British thermal units. In the Almond coal weathering seems to 'have altered the coal to a distance of more than 227 feet along the entry and 103 feet below the surface. Part of this weathermg no doubt is due to the circulation of air along the old mine entry; and in the lower bed the alteration extends back more than 575 feet. Unweathered coal from this mine gives over 13,000 British thermal units on the moisture and ash free basis. In the Black Buttes coal weathering seems to have progressed to a point 100 feet down the slope, or approximately 40 feet l3elow the surface. Unweathered coal from this mine has a fuel value of more than 13,100 British thermal units on the moisture and ash free basis.

The analyses show that the proportions of the various constituents are about the same whether the sample of coal was taken near the surface or at a greater depth, the only exception being the oxygen, which in every case is perceptibly higher near the surface than at greater depths and by its excess shows the extent of the surficial belt of weathering. The ash, sulphur, and hydrogen content remain fairly constant. There appears to be a sUght increase in the amount of liydrogen and ash in the samples obtained near the surface, with a con'csponding decrease in the amount of sulphur. It appears from this that the belt of surficial weathering is one of marked oxidation and in this field for the most part lies near the surface, in few places, if anywhere, extending to the ground-water level. If the coal is not open or exposed to the air, the weathered zone does not as a rule extend more than 150 feet down the dip of the beds, or 50 feet below the surface. Along slo})es and mine or prospect entries the coal weathers back several hundred feet from the mouth of the mine and several hundred feet below the surface. It is known that in one old mine the coal has changed at least 20 feet back from the face of an old entry approximately 227 feet down in the mine and that deterioration extends back into the mine 575 feet from its mouth. It is very probable that in an abandoned mine remaining open to the air oxygenation in time extends throughout tlie mine and that the coals of lower grade show the effect of oxygenation much more than the high-grade coals.

Coal Of The Denver Basin, Colorado.

By George C. Martin.

During the summer of 1908 the writer made a hasty recomiaissance examination of the coal field lying just east of the Front Range of the Rocky Mountains and extending from a point somewhat south of the city of Denver to the north line of the State. As the primary object of the work was the classification of the land, only sufficient time was devoted to the stratigraphy and structure of the rocks to enable the writer to compare his conclusions with those of the previous report** by the Geological Survey on this field. No important difference was found, and since the stratigraphic conditions to the north as far as the Wyoming state line are essentially the same as in the Denver region the statements of that report may be considered as applying to the whole field covered by the present paper.

In general the sedimentary formations are steeply upturned against the mountains, but a few miles away the effect of the uplift disappears and the strata are either horizontal or dip slightly, toward the east at about the same rate as the slope of the plain. The structure is somewhat complicated near the mountain front by the sharp upturning of the rocks and by minor folds and small faults, which have caused considerable trouble in the mining of coal in this district. This condition, however, is local, and as the throw of the faults is small it has not proved to be a great detriment to the field.

The principal coal beds occur in the lower part of the Laramie formation, which outcrops in a narrow band from a point west of Sedalia nearly to Marshall and there on account of faults and flatter dips expands into a wide belt of outcrop which extends northeastward from Marshall to Louisville and Erie, thence northward almost to the Wyoming state line, where it is covered and concealed by a wide overlap of Tertiary rocks.

Active mining on these coal beds has been carried on for a long time, and in 1908 the combined coal production of Weld, Larimer, Jefferson, Adams, and Arapahoe counties, in which they are situated,

oEmxnonfl, 8. F., Croas, Whitman, and Eldridgc, G. H., (leology of the Denver Basin In Colorado: Hon. U. S. OeoL Surrey, vol. 27, 189G.

298 Contributions To Economic Geology, 1908, Part Ii.

was 509,038 short tons. The coal meets with a ready sale, although it is inferior to much of the coal from other fields of Colorado, its nearness to a large city and to a region of intensive farming more than offsetting its poor quality.

The coal generally is shiny and black and is inclined to be massive except as it separates along the planes of bedding. Joints are poorly developed and the coal breaks along irregular lines rather than in prisms like coal of a higher grade. On exposure to the air it rapidly parts with its moisture and in the consequent shrinking it breaks to pieces oc air slacks. Its percentage of moisture is large, and consequently shipment is expensive. Generally it is shipped in box cars to prevent the escape of moisture and the breaking down of the lump coal.

During the present work a number of samples were taken from the mines of this basin for chemical analysis, and as the sampling and chemical work were done uniformly the results are particularly valuable in that they may be compared directly without the possibility of doing injustice to the product of any particular mine. The sampling, which is by far the most important part of the analytical work, was done by cutting a channel across the coal betl, including everhing except the partings or lenses of foreign material which are present at many places. This cut included the entire bed or such part or parts thereof as arc mined at that particular place. After boini: crushed in the mine tb avoid loss of moisture and quartered in the usual way the final sample, weighing about 8 pounds, was sent to the chemical laboratory in sealed galvanized-iron cans. By this method tlie sample reached the laboratory in practically the same condition as it was in at the mine. As in tliis condition it may have included considerable moisture that in no way belonged to the coal, the sample was air dried in tlie laboratory to drive off all excess or easily separated moisture and then analyzed in the regular manner.

Each analysis is given in four forms, so that it may be convenient for a variety of uses. The different forms are as follows:

1. As received: Analysis showing composition of the coal as it comes froju the mine.

2. Air dried: Analysis of sample after it has been exposed to a temperature a little above that of the ordinary atmosphere and to a current of air. The sample in this condition probably is nearly the same as commercial coal, especially if the latter is shipped in box cars.

3. Dry coal: Analysis recalculated to represent the coal after all moisture has been removed. This form is valuable for purposes of comparison, but it should be clearly that it does not represent the coal as mined or as it reaches the consumer.

Coal Of The Denver Basin, Golobado. 299

4. Pure coal: This heading is not strictly correct, for it implies that no foreign material is present, whereas the sulphur has not been eliminated. It is a convenient term, however, and is used in this report to represent coal in the hypothetical condition of having all its moisture and ash removed. Like form No. 3, this is convenient for certain calculations, but in no way represents the coal actually mined and used.

The chemical analyses of samples collected during the course of this work are as follows:

300 CONTBIBUTIOKS TO ECONOMIC GEOLOQY, 1908, PABT n.

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304 CONTBIBUTIONS TO ECONOMIC OEOLOQY, 1908, PABT n.

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The South Park Coal Field, Colorado.

By Chester W. Washburne.

Introduction.

The coal field described in this paper is located in the eastern part of South Park, an intermontane depression in central Colorado. The Kenosha Range on the northeast and the Puma Hills on the east of the park are western spurs of the Front Range of the Rocky Mountains. West of the park lies an irregular group of mountains called the Mosquito Range, beyond which is the Ieadville mining district.

The following pages contain a brief summary of the results of a reconnaissance made in September, 1908. The topography and geology in the vicinity of the coal outcrops were sketched from traverses carefully tied to land comers, but elsewhere no attempt was made to do detailed work.

No coal is now produced in South Park. Between 1875 and 1893 the King mines, near Como, were worked on a large scale by the Union Pacific Coal Company, but they were abandoned after the best and most easily available coal had been mined. It is probable that extensive operations will not be resumed for many years, because of the difficulty in finding coal beneath the cover of gravel and weathered rock and of the apparent absence of thick coal beds.

General Geology.

The general geology of South Park may be briefly summed up in the statement that the park consists of two downthrown fault blocks between the Mosquito Range on the west and the spurs of the Front Range on the east. The eastern fault block, which includes the greater part of the area that is possibly underlain by coal, is a syncline, the eastern limb of which is cut off by the fault tliroughout th<) central part of the field. The western fault block, in which the coal formation remains only as a small remnant west of Como, has a monoclinal structure, its beds rising gradually westward to the summit of the Mosquito Range, where they are terminated by the great London and Mosquito faults."

Geology and mining Industry of Lcadvillc, Colo.; Mon. U. S. (Jeol. Survey, vol. 12, ISWi.

308 Contributions To Economic Geology, 1908, Part H.

The coal beds are involved in both folds and faults. In the western block they dip 45° E. until cut oflF by the South Park fault underneath Corao. In the eastern fault block the coal is folded in a syncline, the eastern part of which has been removed by faulting, as shown on the map (PI. XVI). A remnant of the east limb of the syncline is preserved at Jefferson Hill, 1 mile north of Jefferson, where the coal bed dips about 50® W. North of this locality the outcrop of the coal bed probably swings around the end of the syncline and runs southward to the prospects in sec. 23, T. 8 S., R. 76 W., where the bed stands nearly vertical. South of these prospects the dips become gradually lower, being about 45° E. at the King mines and 20° E. near the south end of the syncline. On following the coal horizon northward from the south end the dips of the east limb of the syncline are found to vary from 30° to 50° W. until the coal bed again disappears against granite at the Elkhorn fault.

As coal occurs only in the ''Laramie'* formation, a description of the other formations is not necessary in this paper.

The Coal..

STRATIGRAPraC POSITION.

The coal beds of South Park occur in what is presumably the "Laramie*' formation, consisting of sandstone with subordinate beds of carbonaceous shale and ranging in thickness from 375 feet down to the vanishinoj point. No fossils have been found in the formation, but as it rests on a yellow sandstone containing upper Montana marine fossils and is unconformably overlain by conglomerate beds that are undoubtedly equivalent to part, at least, of the Shoshone group, as typically developed in the Denver Basin, it seems to correspond to the Laramie according to King's definition.

Three coal beds are present in the ''Laramie" where the entire formation is present. The lowest coal bed, which is usually the best, is regarded as the base of the formation and rests directly and conformably on the upper Montana sandstone. The second coal bed occurs about 187 feet above the lower coal in sec. 23, T. 8 S., 11. 76 W., and about 175 feet above it in sec. 2, T. 9 S., R. 76 W. The upper coal bed lies about 221 feet above the middle coal in sec. 23, T. 8 S., R. 76 W., and 175 feet above it in sec. 2, T. 0 S., R. 76 W.

The formation attains its maximum thickness between sees. 23 and 2, mentioned above, where all three coal beds are present. About a mile south of sec. 2 the unconformity at the top of the ''Laramie" cuts down into that formation, which within a few miles completely dies out, allowing the conglomerate to rest directly on the marine upper Montana sandstone. This condition prevails over the greater part of the coal field, and the "Laramie" is therefore absent in most places where it should normally occur. The details of its distribution are iven in the following pages.

South Park Coal Field, Colorado. 309

Distribution.

The most northern exposure of coal in South Park is on JeflFerson Hill, on the southern margin of T. 7 S., R. 75 W., about a mile north of the town of Jefferson. Here thin beds of coal were discovered in a well dug at Mr. Lilley's house, near the southeast comer of sec. 32. About 12 or 14 inches of coal is reported from a small abandoned prospect 300 feet west of this well. Samples of this coal, which had been dug about ten years, were shown to the writer by Mr. Lilley. The coal appeared to be of good quality, very hard and brilliant, and to show well-developed cubical cleavage. Coal smut was brought up by the drill from a horizon about 20 feet above the coal bed on which the prospect was driven. On Jefferson Hill the coal-bearing formation has a possible thickness of 250 feet.

In this township the position of the coal bed is entirely unknown except on Jefferson Hill. The location of the dotted line on the map that marks the hypothetical position of the coal bed is based largely on the supposition that the sill of porphyry which outcrops at Sheep Rock lies parallel to the sedimentary strata. It is possible, however, that this porphyry is intruded along a fault and that the coal bed is cut off by the porphyry and does not bend around toward the west in the manner indicated on the map. There appears to be no way of determining the position of the coal bed. Deep drilling would not be likely to strike it on account of the high dip of the rocks. South of the Jefferson Hill locaUty there is no exposure on the east limb of the syncline. The coal bed probably runs into the granite at some place in the southern part of T. 8 S., R. 75 E.

West of Jefferson Hill the north end of the syncline is not exposed. The coal bed may possibly encoimter intrusive igneous rocks, as mentioned above, but more probably it lies concealed beneath the alluvium. The southeast comer of T. 7 S., R. 76 W., within which the coal must outcrop if present, is entirely covered by alluvium. The position of the bed indicated by the dotted Une on the map is only a rough guess at the place where the coal may outcrop if present. This line may be as much as a mile too far northwest or half a mile too far southeast. It is given a curved form in order to make it more or less parallel with the outcrop of a deformed sill of igneous rock that is exposed conspicuously at Sheep Rock and other places. It is not likely that the coal bed remains beneath the conglomerate in this locality, because elsewhere in the park it has generally been removed by pre-Shoshone erosion, indicated by the vinconformity mentioned above. Wherever measured in South Park tlie coal bed is not workable except near Como, in the southern part of T. 8 S., R. 76 W., and the northern part of T. 9 S., R. 76 W. As the rocks of tlie South

310 Contributions To Economic Geology, 1908, Part Ii.

Park reon are so deeply weathered that it is necessary to penetrate about 50 feet below the surface before reacliing fresh coal, as the coal-bearing rocks in T. 7 S., R. 76 W., probably lie at angles of 45° to 90°, and as they are covered by an unknown amount of alluvium, possibly more than 100 feet thick, it seems improbable that coal will be foimd in tliis township, even if it is present.

In T. 8 S., R. 76 W., the ''Laramie" formation is exposed in the old Como mine, about half a mile northwest of Como, and in several prospects in sees. 23, 26, and 35. It is also reported in a prospect in the NW. NE. sec. 19. The formation is absent in places, but where present ranges in thickness up to 425 feet, the variation being due to erosion which took place before the deposition of the overlying conglomerate of Shoshone age. The formation consists principally of sandstone and contains from one to three beds of coal.

It is said that at the old Como mine, in the NE. SE. sec. 29, T. 8 S., R. 76 W., which was abandoned in 1883, there was a pocket of coal 5 to 6 feet thick extending along the strike for about half a mile. At a distance of 300 feet down the slope a fault was encountered wliich brought sandstone against tlie coal. Operations were stopped at this fault. Tlie writer believes that the downthrow is westward and that the fault is not large enough to repeat the outcrop of the coal bed. If this conclusion is correct, there must be a good bed of coal imderlying the western margin of the SW. J sec. 28. The conglomerate of the Shoshone group isexposed in a large wellsunkby the Colorado and Southern Railway in the NP]. i SW. sec. 28. This occurrence substantiates the idea that coal could be found by drilHng through the alluvium in the western part of sec. 28. The Como mine was inaccessible in 1908, being entirely caved in and filled with water. Many people in Como substantiated tlie report that tlie coal bed was 5 to 6 feet thick. Only one coal led was reported, but it is believed from the distribution of the prospects that two beds may be present.

The following reference* to tlie mine made by A. C. Peale in 1873 partly this opinion:

Near Lwhnor's ranch a shaft has boon sunk about 30 feet deep, cutting a coal bed about 12 foot in thioknoss, with a dip of 45° NE. and a strike S. 45° E. The clay above the coal is about G inches and below the coal 10 inches thick. Below the lower clav is a sandstone, at the bottom of the shaft, and above the upper clay a bed of yellow soft sandstone. About 200 yards to the west another shaft has been sunk, exposing a bed of coal G feet thick. I am inclined to think there are two different coal beds here, though there may be but one. The slope underlaid by the coal strata extends up close to the sides of the mountain, and the surface is so covered with drift that it is only by means of these shafts that the Lignitic beds can be seen at all. A few fragments of deciduous leaves have beini collected here, .showing clearly that a portion of the Lignitic group, as seen on the east side of the mountain range, occurs here.

a Seventh Ann. Kept. U. S. Geol. and Geog. Survey Terr., 1873, p. 38.

South Park Coal Field, Colorado. 311

In 1876 W. B. Potter** describes this mine as follows:

The Lechner coal [isj worked by Mr. George W. Lechner, miles from Hamilton and 8 miles northeast of Fairplay, in the South Park. The seam is about 12 feet thick and the coal is of rather dull luster, uneven fracture, and exhibits a tendency to slack when exposed to the air and when heated. It burns freely without changing form and yields no coke.

On the north side of Tarryall Creek, in the NW. i NE. sec. 19, T. 8 S., R. 76 W., Mr. Rogers showed the writer a prospect where a few inches (6 to 10 ?) of coal was found several years ago. This prospect had caved in and was filled with gravel from the wash of Tarryall Creek.

In the belt of coal extending through sees. 23, 26, and 35, T. 8 S., R. 76 W., three coal beds are present. Of these beds the lower one appears to be the best, but it is not workable at Mr. Arthur's prospect, in the NW. SE. sec. 23. At this place there is about 12 inches of bony coal at the horizon of the lower coal bed. In Mr. Dunbar's prospect, near the north quarter comer of sec. 26, about 2 feet of dirty coal and bone are exposed, according to the report of people in Como. The coal contains many partings of carbonaceous shale, and is not workable. In a prospect in the SE. SW. i sec. 26, sunk by Judge Foote, about a foot of clean coal and 3 to 4 inches of coal smut are reported at a depth of 45 feet. It is probable that this prospect was not deep enough to get through the zone of surface weathering, which is unusually deep in tliis region and has a marked influence in reducing the apparent tliickness of the coal bed. At Mr. Arthur's second prospect, on the middle (?) bed, in the SE. i SW. sec. 26, about 300 feet east of Judge Foote's prospect, 18 inches of clean coal was found at a depth of about 20 feet. The thickness increased to 22 inches at a depth of about 45 feet, remaining constant at this figure to the bottom of the prospect, which was about 60 feet deep at the time of the writer's visit. The coal, however, was not fresh even at that depth, although probably the bed had reached its full thickness. In spite of the high dip of the rocks, 45®, it is thought possible to work the coal bed for local use. A company known as the South Park Coal Company has been organized for this purpose by John Arthur, of Canon City, M. B. Burke, of Cripple Creek, and others.

The third or highest coal bed is very poorly developed, according to all reports, and is doubtless of no value in this township. It is said that at a prospect on this coal bed sunk about twenty years ago in the SW. SE. sec. 23, there was about 18 inches of dirty coal.

The rocks between the coal beds are not visible except at a few small exposures. In sec. 23 the stratigraphic interval between the lower and middle coal beds is 187 feet and that between the middle and upper coal beds is 221 feet.

a The lignite coals of Colorado: Trans. Am. Inst. MIn. Eng., vol. 5, 1877, pp. 3('>5, 375.

312 Contributions To Economic Geology, 1908, Part H.

In sees. 2 and 11, T. 9 S., R. 76 W., are located the old King mines of the Union Pacific Coal Company. At this place is the best development of coal known in the South Park region. In these mines, which were abandoned in 1893, three coal beds were worked, of which the upper two are said to have varied in thickness from 4 to 6 feet and the lower one from 7 to 40 feet. This lower bed had an average thickness of 7i feet in the upper part of the mine and of 8 feet in the lower part. It was 8 feet thick at a depth of 2,000 feet, the maximum depth reached in mining. The thickness of 40 feet was apparently due to a large pocket about 500 feet in depth and 1,000 feet in length. It is thought to be the result of shearing and crumpling. Several pockets front 15 to 20 feet thick are reported as occurring in other parts of the mine. A section of the bed measured in 1908 is as follows:

Section of coal strata in S. J sec. 2, T. 9 S., R. 76 W.

Ft. In. Upper coal not exposed.

Rock, principally sandstone, not exposed 150

Sandstone, massive 25

Coal, middle 2 9

Sandstone, thin bedded 8

Rock, principally sandstone, not exposed 167

Coal, lower 7

The upper coal bed is said to be 4 feet thick, but this statement can not be verified. The lower coal bed rests on sandstone wliich contains upper Montana fossils. The intervals between the coal beds are variant, owing to changes in thickness of the beds due to differences in original deposition or to subsequent deformation and to the injection of small masses of igneous rock.

The condition of the King mines in 1902 has been described by R.C. Hills as follows:

Slopes No. 5 and No. c turn out about 150 tons per day. ♦ ♦ ♦ The inclination of the wealern outcrof) ranges from 30° to 50°, being about 45° at No. 5 and 33° at No. 6, but less than this to the southward. Along the eastem border the Laramie outcrop is overlap})ed by what is pr()])ably the post-Laramie formation, which is found resting on the border of the granite hills bounding the district to the eastward,.

The seam worked at No. 5 contains from 5 to 7 of coal in the lower bench and 2 feet in the upper bench, which is separated from the lower by from 8 inches to 3 feet of shale. AtNo.G, which is about a mile south of No. 5, the seam worked is only 4 J feet thick. It is not certain that these openings are on the same seam, though this appears most probable. But the intrusion, both above and below the coal, of sheets of eruptive conglomerate which, a short distance south of No. (], consolidate into one large body and thus determine the southern limit of the productive outcrop, throws some doubt on the identity of these seams until further extension of the respe<!tive workings shall have settled the question. Workable coal has been up some disfancc north of No. 5, but the locality is badly faulted. There is also another opening near the railway track

a Tho voiil fiolds of Colorutlo: Mineral Resources U. S. for 1892, IT. S. C.eol. Survey', 1893, p. 338.

South Pakk Coal Field, Colorado. 313

[Como mine], on the oppoeite side of the Laramie area. The South Park coal cakes strongly, ♦ ♦ ♦ but, all things considered, the district has less prospective value than any other independent area in the State.

Arthur Lakes" reports that the principal coal at the King mines is 7 feet thick, but that many faults hinder development. He states that in 1885 the production of No. 1 mine was 58,997 tons.

In the N. § sec. 2 the horizontal distance between the upper and lower coal beds is 600 feet. The dip is variant, ranging from E. to and averaging probably about 45° E. The thickness of the rocks between the upper and lower coal beds is therefore about 425 feet, including a 50-foot intrusive sill of hornblende andesite and about 375 feet of sedimentary strata.

In the SW. NE. J sec. 14, T. 9 S., R. 76 W., 4§ feet of clean coal is exposed in a coal prospect. This is thought to be the lower coal bed, but it may be the middle bed. In a prospect in the NW. J SE. J sec. 14 about 2 feet of coal was seen, but the bottom of the bed was concealed and could not be reached by the means at hand. At this place the coal bed is overlain by 8 feet of thin-bedded soft yellow sandstone, at the top of which is an erosional unconformity followed by conglomerate of the Shoshone group. As this is doubtless the lowest coal bed, it is evident that the upper beds and the rest of the "Laramie'' formation had been removed by erosion before the deposition of the conglomerate. It is thought that south of this point the "Laramie" is entirely removed for several miles. In the SW. J SE.J sec. 14, three-eighths of a mile south of the last-mentioned locality, the conglomerate was found resting directly on the marine upper Montana sandstone (Fox Hills?). A similar observation was made in the NW. J NW. J sec. 35. No trace of coal could be found along the outcrop south of this point, although the debris ejected from prairie-dog holes was thoroughly examined and a prospecting drill was used about every half mile along the line where the "Laramie" should outcrop if present. There are no good exposures of the formation, owing to the covering of talus from the more resistant overlying conglomerate.

A few thin beds of coal were found Ln a prospect in the NE. J NW. J sec. 21. At this locality the rocks strike east and west and dip about S. The "Laramie" formation is entirely covered by alluvium. It is probably cut off on the west by an intrusive mass of andesite porphyry. In sees. 29 and 32 the coal bed may possibly be present along the western margin of the andesite, as sandstone that resembles that at the top of the Montana group (Fox Hills? sandstone) is exposed near this margin. However, no trace of coal, carbonaceous shale, or sandstone of the "Laramie" formation could be found in these sections.

a The South Park coal field (Coloradol: Min. liep.. vol. 51, 1905, pp. 428-429.

314 Contributions To Economic Geology, 1908, Part Ii.

No sign of coal was found in following the formation through T. 10 S., R. 76 W., although careful search was made for it by using a prospecting drill with which a depth of about 15 feet could be reached. In going southward the first sign of coal was obtained in the NW. J SE. sec. 5, T. 11 S., R. 75 W., where the drill brought up some coal smut. Coal is exposed a short distance southwest of this point, in prospects in the southern part of the small syncline that runs through sees. 8, 17, 16, 21, and 28. The coal bed coidd not be accurately measured, but probably is less than a foot thick. The only place where the 'Laramie'' rocks are well exposed in tliis township is on a bluff in sec. 25, at the south end of the outcroj) of rocks of the Shoshone group. Here there is about 50 feet of sandstone, barren of coal but containing layere of carbonaceous shale which may possibly belong to the "Laramie'' formation. It rests conformably on marine uppei Montana sandstone (Fox Hills?) and is unconformably overlain by conglomerate.

In a prospect nearMyner s old house, in the NW. NE., sec. 28, 12 inches of coal is exposed. The coal is overlain and underlain by yellow sandstone. Fragments of coal were found on the (hips of old prospects in the NW. SE. and the SE. SW. sec. 21.

The coal zone is not exposed on the east limb of the syncline in T- 11 S., R. 75 W. The "Laramie'' outcroj), if present, is concealed in places by debris from the of conglomerate on the west and in places by from the granite hills on the east. On account of the apparent great quantity of debris it was thought uselcvss to attempt to reach the coal with the short chill that was used in the field. The exact location of the coal horizon on the eastern Hmb of the syncline in this neighborhood is not known, but it must be very close to the* position of the Montana-Shoshone boundary shown on the map and probably runs into the granite along the Elkhorn fault near the* northern edge of T. 1 1 S.

The rocks may ])ossibly be present on Ridge, but no evidence of them could be found, although the underlying marine upper Montana sandstones are expostul on the west side of the hill, and the overlying conglomerate of the Shoshone group ia exposed on the east side of the hill. Between these two, on the summit and west slope, is a large mass of igneous rock consisting of andesite breccia and biotite por])hyrite, the debris of which probably conceals any 'Tiaramie'' rocks that may be present. It is possible that the "Laramie"' may be found on one side or the of this igneous mass, (4ther along the western foot of the ridge or oust of the summit. Careful search during the reconnaissance of 19()S to reveal any trace of the formation on this ridge, (xcept at the old in the NE. XW. 1 sec. 21 , T. 0 S., R. 70 W., where n hw thin beds of coal were found in yellow sandstone, probably of "Laniniie" age. The

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South Park Coal Field, Colorado.

sandstone strikes nearly east and west and dips about 15° S. It is entirely concealed by alluvium except in the prospect. On the east it must terminate at the South Park fault, and on the west it is probably cut off by the intrusive mass of porphyry and andesite breccia mentioned above.

Character.

No fresh samples of the South Park coal could be obtained and consequently no chemical analyses were made during this examination. The only analyses available are two made a number of years ago when the mines of the field were in active operation. These analyses are as follows:

Analyses of coal samples from the South Park coal fields Colorado

Lochner mine a , Mine No. 5 6...

Proximate.

Ultimate.

Moisture.

Volatile I Fixed matter. ' carbon.

Ash.

Sulphur.

Hydrogen.

Carbon.

Nitrogen.

Oxygen.

a Potter, W. B., Trans. Am. Inst. Mln. Eng.. vol. 5. 1877, p. 368.

ft Hills, R. C, Mineral Resources U. S. for 1892, i:. S. (Jcol. Survey, 1893, p. 362.

Although the quoted descriptions differ somewhat regarding the character of the coal, there can be little doubt that most of it is bituminous. It has well-developed cubical joints, is hard and lustrous, and gives a black streak. It is said that the coal cakes rather poorly in the beehive oven and that a large plant erected at Como about 1880 for the manufacture of coke did not obtain a good product. The coal stocks remarkably well, as shown by the fact that large lumps 6 inches or more in diameter were dug out of the dumps of the old mines, where they had been partly exposed to the weather for over ten years. These fragments were firm and hard, and although they broke readily along the joint planes when struck by the hammer, they did not crumble as a coal of poor grade certainly would after so long an exj)()sure. When the Pishel test for determining coking coal is applied to these fragments they respond very poorly, the pulverized coal adhering but slightly to the sides of the mortar, but as weathering interferes greatly with the coking quality of coal, this can not be regarded as a fair test. Owing to the fact that all the mines had been abandoned many years before the writers visit and were full of water or choked with debris, it was impossible to procure a fresh sample of coal for analysis. The outcrops of the coal are badly weathered, in places to depths of 50 feet or more, and they are covered by alluvium and talus to depths ranging from a few feet to several hundred feet. There are no natural exposures in the park.

316 Contributions To Economic Geology, 1908, Part H.

Conclusion.

The coal of South Park is bituminous and of excellent quality for steaming purposes. The quantity available is unknown, and it seems unZ LT the scanty evident obtained during this exammation to attempt any estimate of this quantity. In none of the prospects examined was the coal of satisfactory thickness. The future of the field is problematical and depends on the discovery of beds of workable thickness. Probably near the old King mines and possibly near the Como mine there is considerable coal which was not removed by the early operations. This can be mined if sufficient care is taken to avoid dangerous flows of water from the adjacent old mines, all of which are completely flooded at the present time.

The Colorado Springs Coal Field, Colorado.

By Marcus I. Goldman.

Introduction.

Location And Extent.

The part of the Colorado Springs coal field described in this report lies in El Paso County, Colo. Its southern limit is the outcrop of the coal-bearing sandstone and shale which extends from the region just north of Colorado Springs in a direction a little south of east to T. 15 S., R. 62 W. The northern limit is indeterminate, for the coalbearing rocks pass under cover in that direction and all development and exploration are less than a mile back from the outcrop; hence statements regarding the presence and condition of the coal at a greater distance are only assumptions. The western limit of the field is also indeterminate, but may be taken as the locality in T. 13 S., R. 67 W., at which the coal-bearing beds pass under the cover of gravel adjacent to the mountains. Coal, however, is not exposed west of the Monument Valley mine, in sec. 1 1, T. 13 S., R. 67 W. In the opposite direction the outcrop of the coal zone can be traced (with interruptions due to a cover of soil) in a direction somewhat south of east for about 40 miles."

The coal outcrop was examined with considerable care, but in the area to the north a much less detailed examination was made.

From its outcrop, as described above, the coal dips gently to the northeast, generally at about 3° to 5° with local increases up to 8° or 10°. From the low dips it is believed that the coal-bearing strata extend under the divide between Platte and Arkansas rivers, coming to the surface again a little south of Denver. On account of this connection the Colorado Springs field is regarded as part of the larger Denver coal region. It also seems probable that the coal-bearing rocks originally continued far to the south, but they have been carried away by erosion, leaving only isolated fields along the base of the Front Range.

a Hills, R. C, Mineral Resources U. 8. for 1892, U. S. Geol. Survey, 1893, p. 332. Storrs, L. S., Twentysecond Ann. Rept. U. S. Geol. Survey, pt. 3, 1902, p. 432.

318 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1908, PABT n.

The Colorado Springs field lies 18 or 20 miles south of the Platte- Arkansas divide, which runs eastward from Palmer Lake, and its general slope is toward the south. The largest stream in the field and the only one that is permanent is Monument Creek, near the western edge. The valley of this stream forms one of the principal lines of communication between Denver and Colorado Springs, and it is utilized by the Denver and Rio Grande and the Atchison, Topeka and Santa Fe railroads.

For some distance east of Palmer Lake the divide is somewhat rough, so that the Colorado and Southern Railroad, which follows a plains route from Colorado Springs to Denver, is obliged to a detour of about 15 miles in order to find a satisfactory grade. The only other obstacle to lines of communication across the plains is Corral Bluffs, about .12 miles east of Colorado Springs.

South of Colorado Springs the valley of Fountain Creek forms the most convenient line of communication with Pueblo, though the country is so open that roads and railroads could be built in almost any direction.

Communication with Cripple Creek through the mountains to the west is of course difficult, yet that town is entered by two railroads from Colorado Springs. The Colorado Midland ascends slowly through Ute Pass, and the Colorado Springs and Cripple Creek District (Colorado and Southern) plunges directly into the mountains North Chovonno Canvon.

Previous Geologic Studies.

Tlie two r('|)orts that contain tlio fullest information on this field arc those of A. Poalo' ami U. C. llills.

At the time Calc's ro|)ort was written there were no mines of any coiniuereial ini|)ortjiiK(\ One known as the (lehrung mine, believed to have been situated on the east bank of Monument Creek, a little south of th( present Carlton mine, liad not proved to be very successful and the old Franeeville mine was not yet open, though Peale states that Ik* went out with Mr. France to the coal, then as now exposed in a stnani course at the west of sec. 19, T. 14 S., R. 64 W. Peale concerned himself mainly with the geology of the foothills and mountains. At the time Hills made his report mining was more extensive, the Francevilh* and McFerran mines had been well developed, and the ext(*nt of the field was understood, though the large mines north of Colorado Springs had not yet been opened.

'1 Ann. Urpt. r. S. Orol. ari'l (Jcou'. Survey . for ls7:i. 1S74. l!)3-270. Mineral Kt'sources f. S. for I'. S. (icol. Survo> , 1nJ3. pj). 311) 3ti5.

Colorado Springs Coal Field, Colorado. 319

General. Geology.

For a fuller account of the general geology of this region the reader is referred to the forthcoming Colorado Springs folio, which is being prepared by G. I. Finlay. For present purposes it will be sufficient to outline the general geology of the beds associated with coal, which was worked out by Professor Finlay and the writer jointly. The discussion begins with the Pierre shale.

Stratigraphy.

PIERRE SlIALE.

The Pierre shale underlies the entire coal field and outcrops in an extensive region to the south and east of Colorado Springs. It is a dark-gray clay shale which in the vicinity of Colorado Springs is approximately 3,000 feet thick. The monotony of this great mass of shale is relieved by the local occurrence of concretions composed of carbonate of lime and carbonate of iron, which weather to small fragments of a rusty brown color. The Pierre shale also contains lenses of gray limestone which because of their relative hardness in places form prominent conical hills known as tepee buttes." The Pierre shale grades upward by an increasing abundance of sand into the overlying Fox Hills sandstone.

Fox Iiills Sandstone.

In places where it has been impregnated with lime the Fox Hills sandstone is of a deep reddish brown color, but the upper portion, near the contact with the Laramie, is generally a light-yellow, nearly pure quartz sandstone. Calcareous sandstone concretions from a few inches up to 3 or 4 feet in diameter, and generally with a fossil imprint of a seaweed at the center, are common in the sandstone.

In most places it is not possible to draw a sharp line between the sandstone at the base of the Laramie and that at the top of the Fox Hills. The latter is typically somewhat micaceous, whereas the former contains minute grains of black chert and no mica. Generally, however, there is no sharp distinction between them. The only exposure in which there seems to be a definite line between the Fox Hills and Laramie is that at Crows Roost, on Black Squirrel Creek. Here the Laramie also is concretionary, but there is a distinct difference in bedding, texture, and character of contained concretions between the two formations.

Laramie Formation.

Above the Fox Hills sandstone lie the coal-bearing rocks of Laramie age. These may be divided into two members — a lower including several massive sandstone beds and three of the most

320 Contbibutions To Economic Geology, 1908, Pabt H.

beds of the field, and an upper composed of clay shale, sandy shale, and some sandstone with poorly developed coal beds.

The best exposure of the sandy, coal-bearing member is in Popes Bluff, where the base of the formation is composed of a massive sandstone from 40 to 100 feet thick, but not sharply defined from the underlying Fox Hills. The upper part of the sandstone member of the Laramie gives way gradually, toward the east, to shale with thin beds of calcareous and ferruginous sandstone about 250 feet thick. In the western part of the field the sandy member is about 200 feet thick.

The shaly member covers more than a square mile west of the Pikeview mine and in section it is well exposed on the slope below Pulpit Rock, where its thickness is about 150 feet.

Rocks Above The Laramie.

Paleontologic evidence, mainly that of fossil leaves, is at present too incomplete to permit definite correlation of the formations overlying the Laramie. In the following descriptions attention is drawn to the lithologic similarities of these rocks to formations in the Denver region, but the subdivision and naming of the beds is left to the future.

Conglomerate, — In some parts of the field the shaly part of the Laramie is overlain by a conglomerate containing some pebbles of sediinentarv rocks but mainly of rusty quartz. The pebbles range from 1 inch to 2 inclies in diameter. In places a very pure, hard white quartzose sandstone takes the place of the conglomerate. The maximum known thickness of the bed is about 30 feet, in an exposure on Monument Creek back of the Curtis mine, a few hundred feet west of tlic Cracijmore sanitarium. The lithologic similarity of this to sonic parts of the Arapahoe formation in the Denver Basin is apparent.

AndeKitlc material. — The conglomerate is overlain by beds of andesiti<' material, which in lithologic composition is similar to the Denver formation. Where exposed in natural outcrop these rocks are mainly yellow, yellowish gnen, and cream colored, with a few beds 1 to 2 feet thick of black, leaf-bearing coaly shale and of limonite, generally not more than 1 foot thick and in placets full of plant fragments. Most of this rock is very soft, so that material from the upper beds washes down over those below, covering the contacts. In places there is a bed composed of well-rounded fragments, averaging half an inch in diameter, of andesite in a matrix apparently of the same material.

The most complete exposuns of the beds containing andesitic material were obscM'ved in the bluffs underlying Pulpit Hock on the west bank of Monument ('reek, opposite Pikeview (see section 22, p. 328), and along the west fork of Jimmy Camp Creek south of the Richfield

Colobado Spbings Coal Fieud, Colobado. 321

Springs ranch and just north of the county road. The pebble bed is present in the Pulpit Rock section, where it is about 18 feet thick.

The average thickness of the beds of andesitic material is about 125 feet.

ArJcose. — Beds of arkose lie unconformably upon the andesitic material and overlap the coal-bearing sandstone in the southeast corner of sec.6,T.13 S.,R.67 W. The arkose has two phases — (1) coarse arkose near the mountains, some sandstone, and clay containing coarse quartz grains; (2) fine-grained, very micaceous sandstone. Both phases are very irregularly bedded, and most of the lithologic units are of small horizontal extent. An exception to this discontinuity is a bed of conglomerate within 10 feet of the base. This was not observed near the mountains, but is well exposed on Jinmiy Camp Creek and was found also in a stream channel just east of the Franceville schoolhouse. The pebbles range from half an inch to 1 inch in diameter and are siliceous, brightly colored, and rounded, and have glossy surfaces. The surface of the road beyond the first crossing of Jimmy Camp Creek south of the Richfield Springs ranch is strewn with these pebbles, but the bed could not be found in place.

The total thickness of the arkose has nowhere been determined. It would, in fact, necessarily be variant on account of the irregular deposition and meager horizontal extent of the material. From this irregularity it is probable that the apparently successive beds encountered in crossing the formation on a flat or gently sloping surface may be equivalent instead of consecutive. The only way to obtain reliable measurements of the beds would be by drilling at places where the formation is well exposed.

The greatest thickness measured in surface exposures of the arkose is about 200 feet in Austin Bluffs and 300 to 400 feet in Corral Bluffa The total thickness, however, is believed to be still greater.

Oravel. — Covering all the formations near the mountains is gravel, mainly of granite dfibris. The boundaries of the terraces covered by the gravel have been mapped only where they cross the coal-bearing formation.

Structure.

The geologic structure of the region adjacent to the coal outcrop is very simple. From the south westernmost point of Popes Bluff to the east end of the strip examined the strike seems to be uniformly N. SO"* W., and the dip ranges from 2° to lO*" NE. The most marked variation from this general structure is in the northwestern part of Popes Bluff, where, as the coal-bearing sandstone approaches the mountains, it is turned up steeply and the strike is more nearly parallel to the trend of the mountains (N. 30® W.). The two most marked variations in dip are the steep dip of 10® on Jinmiy Camp Creek and the flattening around FrancevQle.

7963**— Bull. 381—10 21

Contbibutions To Economic Geology, 1906, Fabt Ii.

Detailed Sections.

The best opportunity for the study of the coal beds and of their relation to each other is afforded in Popes BluS and adjacent exposure on the west side of Monument Creek. Numerous sections were m&de here, as well as at other places along the outcrop, and the most representative of these are given on the following pages. The facts shown by these sections are discussed on pages 332-335,

Seetiont of coal bedt and eoat-staring rodt in Colorado Sprinfaftld.

[NuDiben of sections correspond to those given OD PL XVU.]

1. Moanmaat VSiMj mlu. ho. 11, T. 11 8.. R. ST W.

Ft. Id.

Sande (one (uppermost beo of lower divinon of tbe Laraniie). 30

Sandstone, femiRinouB 6

Interval, mainly nhale 57

Sandslone 2 6

Interval, mainly shale

Clay, carbonaceouBj ,

0l bedB ;

Coal,8andy J ' '

t. Abudoud . mc. It. T. 11 8., S. IT V.

a. Section al mine mouth.

Ft. Id.

Clay, pink, containing (ossil plants 3

Clay 1

Coal 1 . jj I 1 10

Sands lone,

b. Section 30 feet down slope. Clay, carbonaceouBl

Coal Ibeil B

Coal, sandy J

70 (eet d.iwii the slop.' lhi> rfiiil bed is 2 feet thiok.

3. Popai Blufli, IK. 14. T. IS S., S. tn W.

Ft. Id.

SandBtone (uppermost bed of lower division of the Ijiremie). .

Inten-al, probably halo 9

Saud, nodular, feirunous 2

Inten-al, mainly shale 50

Sand, containing nodular concretions of iron 1

Shales, gray and carbonacootis 10

id, witi lerrupiiirms nortiiles and imprcsaiona ol plants 1

Mift, femipnouc 2

cubanaceoua I

Colorado Sfbings Coal Field, Colorado. 323

Ft. In.

SandBtone, soft, yellow 4

Shale, greenish 1 6

Shale, carbonaceous 3 6

Sandstone 3

Coal 2

Shale, carbonaceous 1

Clay, greenish.' 6 6

Shale, carbonaceous 1 6

Clay, sandy 3

Shale, carbonaceous'

Coal

Coal, bony f" ] 5

Coal, sandy J 5

Sandstone 19

Conglomerate 2

Shaly coal 6

Sandstone 1 6

Coal, sandy, bed A 7

Sandstone, gray, massive 15

163 9 4. Popes Bluffs, see. 8S, T. IS S.. R. 67 W.

Ft. in.

Sandstone (uppermost bed of lower division of the Laramie) 15

Interval, mainly shale 60

Shale, carbonaceous 4

Sandstone, argillaceous 4 6

Shale 8

Shale, carbonaceous 1

Sandstone 1 6

Shale, carbonaceous 3

Coal, bed B 10

Sandstone 23

Shale, sandy 2 6

Shale, carbonaceous 2

Sandstone 2 10

Coal, sandy, bed A 1

Sandstone 3

Interval, probably sandstone 12

Sandstone, gray 18

160 4

i, Co&l proipeot on east side of Popes Bluffs, see. 8S, T. 18 S., R. 67 W.

Ft. In.

Sandstone 5

Clay 4

Coal..:

Clay and bone Coal

12 X

324 Contributions To Economic Geology, 1908, Part U.

6. Popes Blnfli, mo. 8S, T. 18 S., B. 97 W.

Ft. in.

Sandstone (uppennoet bed of lower division of the Laramie) 20

Shale, gray 3

Shale, carbonaceous 18

Sandstone 30

Shale, carbonaceous 12

Sandstone, yellow, shaly 2

Shales, light gray and brown, with coal bands 3 to 4 inches thick. 45

Sandstone, soft 2

Shale, carbonaceous

Coal

Sand, coaly

Sandstone, massive, gray 25

Shale, carbonaceous, coal, bed A (?) ' 4

Sandstone, gray 1

166 10

7. Popes Bluffs, sec. 24, T. IS S., B. 67 W.

Ft. In.

Sandstone (uppermost bed of lower division of the Laramie) ... 25

Shale, greenish 25

Sandstone, soft, argillaceous 12

Shale, carbonaceous 2

Sandstone 3

Shale, carbonaceous 5

Shale, greenish 8

Sandstone 3

Shale, carbonaceous 5

Sandstone, ferruginous 6

Shale, gray 3 6

Sandstone

Coal

Sand, soft, coaly

Iron nodules

Sandstone, massive, gray 25

Shale, brown, carbonaceous, coal, bed A(?) 3

Shale, sandy 1

Sandstone, gray, ma8sive 40

Sandstone, greenish 40

218 4 8. Sec. 19, T. 18 S., B. 66 W.

Ft. in. Sandstone (uppermost bed of lower division of the Laramie).

Interval 34

Coal 1 4

Shale 8

Sandstone 14

Shale, carbonaceous 2

Sandstone and sandy shale , 37

massive, gray 13

Shale, carbonaceous] f 1 6

Coal 3

Shale, carbonaceous I ) 6

Coal J [l 7

Shale, brown, sandy 6

Sandstone.

113 8

Colorado Springs Coal Field, Colorado.

9. 8m. 19, T. IS 8.. R. 66 W.

Ft. in. Sandstone (uppermost bed of lower division of the Laramie).

Interval, mostly shale 12

Coal 1 6

Shale and sandstone 28

Shale 5

Coal, bed C 11

47 6

10. 8m. 19, T. IS 8., R. 66 W.

Ft. In.

Sandstone 3

Coal 6

Shale, carbonaceous 2 1

Clay.

r 2

Coal

Shale, carbonaceous

Clay

Sandstone, yellow 2

Shale, gray

Sandstone, soft, yellow

Shale, light gray with coal intrusions 3

Sandstone, gray 16

Coal bed B, not well exposed.

11. 8m. 24. T. 18 8., R. 67 W.

Ft. In.

Coal 6

Shale, carbonaceous 2

Clay 1 6

Ft.

In.

f

Sandstone 6

Shale, carbonaceous/ I 6

Clay.

Below this section coal bed B is exposed with a thickness of 8 inches.

18. if oath of progpMt In mo. 84, T. IS 8., R. 67 W.

Shale, carbonaceous

Coal

Bone >bed C.

C/oal, bony

Shale, carbonaceous.

Clay.

18. 8m. 84. T. 18 8.. R. 67 W.

Ft. in.

Sandstone (uppermost bed of lower division of the IAramie) 20

Shale, gray 25

Sandstone, soft 18

Shale, gray 8

Shale, carbonaceous 3

Coal 2

Shale, carbonaceous 5

Shale, gray 3

Sandstone, massive, yellowish, gray 10

Bone] f 5

Coal IbedC 1 10

Bone

326 Contributions To Economic Geology, 1908, Pabt 11.

Ft. in.

Clay 4

Sandstone 25

Shale 2

Shale, carbonaceous 1 6

Shale, containing some coal

Coal.

Bone

Shale

150 9 14. Coal irotpeet In mo. 84, T. IS 8., R. 97 W.

Sandstcxie. Ft. in.

Coal, bed C 3

Shale, brown, carbonaceous 2

Clay, green 3

Sandstone 30

Coal, bony 1

Clay, gray Ibed B

Coal, hard, bright, conchoidal

Clay 1 11+

40 3

The prospect slope, about 200 feet long, was driven in mostly on coal bed B, but the end of the slope the bed is in about the same condition as where it was first struclc*

16. Yard! of Colorado Brick and ArtUelal Stone Company, sec 19. T. IS 8., R. 66 W.

Ft, In.

Shale, greenish yellow 4

Sandstone, soft, ferruginous 5

Shale, gray, with carbonaceous and ferruginous partings 7

Sandstone, soft, white, massive 30 '

Clay 3

Sandstone, soft, gray, massive 17

Shale, with yellow gypsiferous sandy layer in middle 30

Coal, bed C 1 6

Clay 1 6

Sandstone, gray, maasi ve 35

Shale, carbonaceous"

Shale, carbonaceouK

Shale

Sandstone, soft, yellow, with shaly layers' 25

Shale, gray 3

Coal Ihed A (

Coal, sandy/ 9

Sandstone.

166 3 16. West bluff along which road runs, sc. 19, T. 13 S., R. 66 W.

Sandstone. Ft. in.

Coal, including about 2 inches of bone near middle!, i / H

Shale, carbonaceous / ""I 3

Sandstone 26

(bal, bed A (?) 2 6

Shale, brown.

32 5 Coal bed A varies from I foot 10 inches to 3 feet in thickness.

Colobado Springs Coal. Field, Colorado. 327

17. Coal bdf In upper part of f onnatloii In mo. 14, T. IS 8., R. 97 W.

Ft. in.

Limonite, concretionary 2

Shale, with limonite concretions 20

Sandstone 1 6

Shale (?) : 10

Shale, greenish gray 5

Shale, carbonaceous 3

Coal 2 2

Shale, carbonaceous 5

Sandstone 6

Shale (?) 5

Shale, sandy 5

Shale (?) 6

Sandstone, gray 10

Sandstone, ferruginous 1 6

Sandstone, cross-bedded 20

Sandstone, massive 25

Sandstone, argillaceous 5

Sandstone, ferruginous 2 6

Shale 8

Sandstone 18

165 1

18. Air thaft of Ifaor mine, mo. IS, T. IS 8., R. 67 W.

Ft. in.

Sandstone, massive 100

Clay, sandy 2 2

Coal, bed C(?) 1

Shale, carbonaceous 1 6

Clay, sandy 35

Sandstone, with coal bands, coal bed B (?) 2

Sandstone, massive 30

Coal, bed A 3

joal bed A is the one worked in this mine. 173 8)

19. Coal progpoot In mo. 19, T. 18 8., R. 66 W.

Ft. in.

Sandstone, massive 13

Shale, carbonaceous with coal lenses

Coal ybedB.

Bone

Clay 25

Coal, bed A.

39 8

0. XTppor part of coal-bearlnc formation weit of Carlton mine, NE. i mc. 18, T. 18 8., R. 67 W.

Ft. in.

Shale, gray 6

Coal 1 4

Shale, carbonaceous 1

Clay, gray 1

Shale, gray (?) 12

Shale, carbonaceous with traces of coal 6

Coal 1

Shale, carbonaceous 1

328 Contbibutions To Economic Geoloot, 1908, Fabt H.

Ft. In. Clay, gray 2

Cool 7

Shale, carbonaceous 3

The middle coal bed in this section varies from 6 to 18 inches within a horizoi: distance of 20 feet. The coal beds are probably lenticular and irregtilar, as the not show in the section back of the Carlton mine.

81. Carlton mine, mo. 18, T. IS 8., B. 66 W.

Sandstone, soft.

Coal, laminated and bony, with 2 inches of sandstone near base

Coal

Coal, **8iliceous," bony

Coal

Coal, bony

bed A..

.

88. Woit lido of Rock, mo. 17. T. 18 8., B. 66 W.

Arkose.

Clay, gray

Sandstone, gray (fossils)

Shale, gray

Clay, purplish brown

Shale, carbonaceous, and gray sandstone

Sandstone, argillaceous

Clay, brownish gray (fossils)

Sandstone, quartzose

Shale, carbonaceous

Tuffs, gray and greenish yellow, with carbonaceous shale

Conglomerate with pebbles of andesite

Tuffs, gray and greenish yellow, with carbonaceous shale

Interval, probably composed of tuff.

Ft. in.

Ft.

io.

Clay and argillaceous sand (fossils) 125

Sandstone, soft, white, with carbonaceous bands

Sandstone, massive, yellow

Clay, sandy

Sandstone, argillaceous

Clay, gray, sandy

Clay, gray

Coal and clay, in tor laminated

Clay, gray, sandy

370 2

The thicknesses given in this section are only approximate, as the dips are and the section was measured along a gently inclined surface.

88. East bank of If onnment Creek, opposite old Williams mine. sec. 19. T. 18 S., R. 66 W.

Sandstone, massive, yellow.

Shale

Shale, carbonaceous'

Bone

Coal

Coal, impure

Shale, carbonaceous. Clay, greenish gray.

bed A.

Ft. in.

Colorado Spbinos Coai. Field, Colorado.

L Onlly on ast bank of KoBUBMiit Creek eait of Plkevlew statloii, eec. 19, T. IS 8., R M W.

Ft. in.

Sandstone, soft, white 5

Coal, sandy 2

Clay, sandy 3

Interval concealed 2

Sandstone, massive 15

Clay, sandy 13

Shale, carbonaceous 3

Clay, sandy 6

Shale, green 20

Shale, carbonaceous

Coal

Shale, carbonaceous

r 2

bed C (?).

bed A

Shale, green 2

Interval, probably shale 3

Sandstone, massive 17

Shale, carbonaceous] 11

Sandstone 23

Shale, mostly carbonaceous

Coal

Shale, carbonaceous

Coal

Clay 3

Shale, greenish 6

Bone

Shale, carbonaceous 2

Bone

Coal, bedA 1

Sandstone 46

87. Curtis mine, lec. 89. T. 18 S., R. 66 W.

176 3 Ft. In.

Shale 3

Shale, sand, and clay 5

Sandstone, massive 13

Shale

Clay, gray 9

Bone I I 8

Bone, with layers of coallj A I 2 2

Coal, bony ' 1 6

Coal 12 9

Clay.

88. Sec. 18, T. 14 S., R. 66 W.

39 4 Ft. In.

Shale, carbonaceous, resembling coal; probably represents a coal

bed 5

Shale, in places sandy 4

Sandstone, massive, soft, ferruginous 1 6

Shale, sandy in upper part 4

Clay, sandy 3

Shale, carbonaceous] f 3

Coal Ibed A(?) i 10

Shale, carbonaceous

330 Contributions To Economic Oeolooy, 1906, Pabt H.

Ft. in.

Sandstone, massive, argillaceous 3 6

Shale, dark gray 4

Sandstone, ferruginous 2 4

Sandstone, soft, yellow, finegrained, quartzose 11

Shale, gray : 2 4

Shale, sandy, ferruginous 2 4

Sandstone 40

77 9 8S. Sao. 19, T. 14 8., R. 64 W.

Goal, not fully exposed, bed B. Ft. in

Shale, yellow, sandy 1 6

Sandstone 1 10

Shale, gray 3

Sandstone 2 6

Clay and shale (fossils) 4

Coal, bottom not exposed, bed A 7

M. DavlAg mine, mo. 89, T. 14 8., R. M W.

Ft. in.

Coal, bony 5

Shale, carbonaceous 6

Clay 2

Sandstone, yellow, massive 10

Clay, carbonaceous 3

Coal 1

Bone 5

Clay, gray 5

Coal ] r 1 1

Coal, bony I bed A I 1 3

Coal

Clay

24 5 36. Stream bank in SE. i tec. SS, T. 14 S., &. M W.

Ft. in-

Coal 4

Shale, sandy 15

Coal 4

Shale, sandy 20

Sandstone, soft, gray 2

Clav, gjav 6

Shale ' 1

Coal 1 2

Shale, carbonace.)iis 2+

42 4+ 37. Alone ftream channel sonth of Bantles ranch, tec. 80, T. IS S.. IL €8 W.

Sandstone. Ft. in.

Clay, carbonacetius 3

Shale, gray 8

Coal. 1

Clay, gray

Sandstone 5

Shale, gray 5

11 Hi

Colobado Springs Coal. Field, Colorado. 331

JlMmj Camp Cxvek; upper part meafiired due eait ttom Blelifleld Bprlafi nmoh and lower

part in aeo. 10, T. 14 8., B. 96 W.

Ft. In.

1. Sandstone, soft, argillaceous (fofisib) 1

2. Sandstone, massive, cross-bedded, tuffaceous. 10

3. Shale, gray 1

4. Shale, carbonaceous 1

6. Shale, gray 6 6

6. Shale, gray, and yellow sandstone 102

7. Shale, carbonaceous 2

8. Shale, gray 4

9. Shale, carbonaceous J

9i. Coal i

10. Clay i

11. Coal 4i

12. Interval, covered 550

13. Arkoee, quartz and feldspar 3

14. Concealed 90

15. Shale, sandy, yellow 37

16. Shale, carbonaceous 1

17. Tuff 41

18. Shale, containing some coal 4

19. Tuff 5

20. Shale, black, carbonaceous 1

21. Tuff 20

22. Sandstone, ferruginous (fossils) 10

23. Tuff 11 6

24. Tuffs, yellow and purple 7

25. Shale 33

26. Sandstone, ferruginous 2

27. Shale 14

28. Sandstone, massive, soft, argillaceous 4 6

29. Shale, yellow and dark gray 22

30. Sandstone, calcareous 2

31. Shale 4

32. Sandstone, soft 27

33. Shale, with ferruginous layers 2

34. Sandstone, soft 2 4

35. Shale, sandy 7

36. Interval, not measurable on account of local increase of

dip and change of strike; estimated 10

37. Shale, carbonaceous 10

38. Coal 2 4

39. Concealed 36

40. Sandstone, ferruginous 2

41. Shale 2

42. Shale, carbonaceous 10

43. Shale,green 17 6

44. Sandstone 4 6

45. Shale, carbonaceous 1 6

46. Clay 1

47. Coal, bed A (?), burned and underlain by coaly sand-

stone 6

48. Sandstone, shaly 8

332 Contributions To Economic Geology, 1908, Pabt H.

Ft. in.

49. Sandstone, gray, massive 24

50. Sandstone, gray, fenoiginous 6

51. Sandstone 4

52. Sandstone, soft, gray, quartzose 27

53. Interval, not measurable but estimated 25

54. Oonglomerate, ferruginous 2

55. Shale, gray 2

56. Conglomerate, ferruginous 2

57. Sandstone, concretionary 20

58. Sandstone, soft (fossils) 25

59. Sandstone, soft, yellow 25

60. Shale, light gray.

1,263 6

From an inspection of these sections it is evident that there are three more or less well defined coal beds. These have been lettered, beginning at the bottom, A, B, and C. Bed A, which is the principal bed, is not well developed west of Monument Creek. At the most easterly of these places (section 15), the coal shows its greatest thickness of 1 foot 3 inches. There seems to be little doubt, however, from its position in the section that the carbonaceous shale and coaly sand shown in many sections and marked coal A is the impure ma ginal portion of the coal bed.

The outcrop of coal bed B where it is 2 feet or more thick is shown on the map (PI. XVII) and its position in the column is indicated in several sections. That the coal which has been prospected and developed along the west face of Pikeview Bluffs is bed B and not bed A seems evident from its position in the sections — from its relation, for instance, to the topmost of the three sandstones that are so well developed in this part of the field.

Although the map shows that a third bed, called coal C, reaches a thickness of 2 feet or more over a small extent of its outcrop in the area of the bluffs under discussion, yet it may be seen from the sections that it is not a persistent bed but rather a local development of coal at different horizons within a shaly band of varying tliickness lying between the middle and upper beds of sandstone.

There is little reason to expect that individual coal and sandstone beds in this section could be correlated with sandstone and coal beds in the \4city of Denver; yet, as a matter of fact, the similarity between the coal-bearing rocks in the two fields is remarkable. Thus, in the western part of the Colorado Springs field and in the Denver field there is a series of basal sandstones up to 200 feet in thickness."** Above this series in both fields occurs an argillaceous formation, but in the lever field tliis is 400 to 1,000 feet thick, whereas in the Colorado field it is only about 150 feet thick. In both fields the sandstone is divisible into three beds with intermediate beds of coal and sliale. Tlie similarity is shown in figure 3.

a Emmons, S. F., Mon. U. S. Geol. Survey, vol. 27, 189C, p. 28.

Colorado Spbings Coal. Field, Colobado.

Between the place where section 7 was measured and Monument Creek a workable though varying thickness of coal outcrops in the banks of the streams. There is no means of determining vrtiich coal bed is worked in the Carlton mine, but from the more extensile development of coal A it is beUeved to be that bed. If this interpretation is correct, however, the thickening is local, for along Monument Creek to the south bed A, as shown in section 6, contains little coal. Coal A is of workable thickness in the WiUiamsville mine, expands to maximum of 14 feet in and near the Curtis mine, and, according to port, thins to less than 3 feet in the Enterprise mine.

SQiioft ot Popes' BluPPs Colorado Springs Held

Section at Marshall. Denver Basin fMon, USaS,NoXXVII P.346J

J.

FrouKK 3.— Sections showing similarity in the arrangement of the coal-bearing part of the Laramie

formation in the Colorado Springs field and in the Denver Basin.

Coal sections 25 to 31 (WiUiamsville to Tudor) show in greater detail the variations in this coal bed. A bed of impure coaly material about a foot thick at both ends of this thick body of coal is well brought out in these sections. In places this bed is almost pure clay and attains a thickness of 2 feet, but benches of coal about 3 feet thick remain above and below it. It is well to bear this in mind in developing the coal of this region and to test occasionally with drill holes through the roof and floor for overlying or imderlying benches of coal.

834 Contbibutions To Economic Geology, 1908, Pabt H.

From an exposure on Sand Creek about half a mile southeast of the Enterprise mme (section 32) to the bluffs on Jinuny Camp Creek no exposure of coal could be foimd, as the rocks are nearly covered by soil. On Junmy Camp Creek most of the coal along- the outcrop has been burned. From records of the old McFerran mine, however, the coal bed is known to have averaged about 6 feet in thickness. A few hundred feet south of the road on the east bank of the creek, in sec. 18, T. 14 S., R. 65 W., an upper coal bed shows but is not weD exposed. Here 2 feet 4 inches of coal was measured without reaching the bottom. This bed is about 65 feet above coal bed A and is tiieiefore in the position of coal bed C.

In sees. 14 and 15, T. 14 S., R. 65 W., there are numerous exposures of coal. Farther east, however, little evidence of the coal bed can be seen until the old Franceville slope is reached, and the first good section of it is found in the creek bank just north of the highway bridge at the west edge of sec. 19, T. 14 S., R. 64 W. Here 7 feet of coal is exposed without showing the bottom. Coal section 36 represents the coal bed in the Davies mine and shows that the coal here is thinner. In sec. 32, T. 14 S., R. 64 W., the cal bed is thinner still and where the outcrop crosses the east line of sec. 5, T. 15 S., R. 64 W., the coal has probably a thickness of only a few inches. More noteworthy than the outcrop of coal A in this strip is the occurrence of a group of upper coal beds (perhaps coal C) in the creek in the NE.i sec. 5. From this point to the east end of the field the only exposure of coal that could be found is a bed 1 foot thick in sec. 20, T. 15 S., R. 63 W. (See section 37.) On Black Squirrel Creek south of Crows Roost ranch the beds at the horizon of the coal are fairly weD exposed, yet no trace of a coal bed could be found. It seems probable, therefore, that along the outcrop in T. 15 S., Rs. 62, 63, and 64 W., there is no workable coal.

(.oal in the shaly member of the Laramie is known in only two places in the field, both near the west end, in sees. 13 and 14, T. 13 S., R. 67 W. (See sections 17 and 20.) At both places the coal has been prospected but the openings are caved. The coal appears bright and clean, but the beds are of varying thickness and apparently of slight horizontal extent. On account of soil covering it was not possible to determine whether the two outcrops are connected.

In this connection Emmons's comment on the coals of the shaly Laramie in the Denver Basin may be noted. **Coal seams have also been found in the uj)})er clayey division, but the coals are lignites [subbituminous in the classification], with higher percentages of water and of inferior economic value.''

Coaly shale occurs in the formation next above the Laramie, but so far as known th( thickness of the coal beds in this formation is so small as to make them entirely negligible.

a Enimons, S. F., Mon. U. S. Gool. Survey, vol. 27, 1896, p. 29,

Colobado Springs Coal Field, Colobado. 835

In the andesitic beds dark-brown shale full of leaf fragments is found and here and there it contains some coal. This is shown in section 38 from No. 14 to No. 24, inclusive.

Above this, in the arkosic rocks along the east bank of Jimmy Camp Creek, east and a little southeast from the Richfield Springs ranch, several small coal beds occur as shown in section 38 from No. 2 to No. 12, inclusive.

These sections show no coal of any practical importance, nor were prospects on coals in the arkosic or andesitic beds found in the part of the field represented in the accompanying map. The thickest bed of coal in the upper formations, as reported in well records, is 10 inches thick, but recently thick beds have been reported several miles north and east of Falcon.

The following list gives the location of the places where sections were measured and samples taken for analysis. The niimbers correspond to those of the sections given above and also to those used on Plate XVII.

1. Monument Valley mine, sec. 11, T. 13 S., R. 67 W. Coal bed B; analysiB No. 6545. Sample taken on south wall of slope 20 feet from mouth. Coal dry, but probably weathered.

2. Abandoned prospect, sec. 14, T. 13 S., R. 67 W. Coal bed B.

5. East side of Popes Bluffs, sec. 23, T. 13 S., R. 67 W. Coal bed B.

6. Popes Bluffs, sec. 23, T. 13 S., R. 67 W. Coal bed B.

10. Prospect in sec. 19, T. 13 8., R. 66 W. Coal bed C.

11. Prospect in SE. NE. J sec. 24, T. 13 S., R. 67 W. Coal bed C; analysis No. 7129. Thip prospect had not been operated recently and coal is probably weathered.

13. Sec. 24, T. 13 S., R. 67 W. Coal bed C.

18. Neer mine, sec. 13, T. 13 S., R. 67 W. Coal bed A; analysis No. 6439. Sample obtained in main entry 130 feet south of foot of shaft.

21. Carlton mine, sec. 18, T. 13 S., R. 66 W. Coal bed A ; analysis No. 6443. Sample taken from face of room 19 off thirteenth entry.

25. Williamsville mine, sec. 29, T. 13 S., R. 66 W. Coal bed A.

26. Danville mine, sec. 29, T. 13 S., R. 66 W. Coal bed A; analysis No. 6442. Sample taken from main slope beyond ninth entry.

27. Curtismine,8ec.29, T. 13S.,R. 66W. CoalbedA; analysis No. 6440. Sample taken from back entry off seventh north entry and represents 6 feet 10 inches of the lower bench.

28. Patterson mine, sec. 32, T. 13 S., R. 66 W. Coal bed A.

29. Rapson mine, sec. 33, T. 13 S., R. 66 W. Coal bed A; analysis No. 6441. Sample taken from third room off fourth south entry and represents 5 feet 9 inches of the main bench.

30. Keystone mine, sec. 4, T. 14 S., R. 66 W. Coal bed A; analysis No. 6546. Sample taken in crosscut being driven as an airway to old workings 50 feet south of main entry and 800 feet from foot of shaft.

31. Tudor mine, abandoned slope, sec. 2, T. 14 S., R. 66 W. Coal bed ?.

34. Cell mine, sec. 30, T. 14 S., R. 64 W. Coal bed A; analysis No. 6438. Sample taken at a point 1,050 feet northeast of mouth of slope.

35. Daviee mine, sec. 29, T. 14 S., R. 64 W. Coal bed A; analysis No. 6437. Sample taken at a point 425 feet northeast of mouth of main

38. Purdon prospect (not in area represented by the map), SE. J NW. J sec. 27, T. 11 S., R. 61 W. Coal bed ?. Analysis No. 7128,

336 CONTBIBUTIONS TO ECONOMIC GEOLOGY, 1906, PABT n.

Character Of The Coal.

There is no marked difference in the character of the coal in parts of this field. In general, it is a lustrous black, rather geneous coal with conchoidal fracture. On close inspection seen to be less homogeneous than appears at first sight, for it i posed of lenses up to a few feet long, and from a small fracti inch up to several inches thick, of a brilliant glossy black coal, in many places the woody structure of the material from was derived, in a matrix of a dull black, more granular The coal slacks readily on exposure to circulating air, brea fragments along an irregular network of cracks. Fossil coxnmon in the coal.

The following analyses were made at the Pittsburg laborai the United States Geological Survey on samples collected duri present examination. Each sample was obtained by making across a face of the coal bed, including such parts as were could be mined to advantage. The descriptions on page 33 the part of the bed that is represented by the sample. Owing fact that not many mines were in operation, some of the sampl taken from old prospect entries, and in such places the doubtless weathered, although all coal showing effects of wea was carefully removed before sampling was begun. In the mines the coal was fresh, having been taken from a recently face.

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Colorado Spbings Coal Field, Colorado.

Development And Marexts.

A brief review of the history of mining in the region, gathered from reports such as those of the state coal-mine inspector of Colorado and from the Mineral Resources volumes published by the United States Greological Survey, is given below.

In the first volume of Mineral Resources* occurs this statement concerning El Paso County:

The only mines worked to any extent are those owned by the Denver and New Orleans Railroad Company at Franceville ♦ ♦ ♦. The product has only become available since the completion of the Denver and New Orleans Railroad in July, 1882.

That coal was taken out for local use before that time is quite possible, but it is impossible to trace the history of such small-scale working of coal seams by any authentic records; very likely such operations began with the earliest settlement of the region.

The Franceville mine was operated from the middle of 1882, apparently, till 1898, which is the last year for which its production is reported by the state inspector of coal mines. During that period it produced the following annual amounts:

Production of Franceville coal miney 1882-1898.

Short tons.

1882 23, 689

1883 54,416

1884 56,070

1885 39, 038

1886 50, 000

1887 47, 017

1888 39, 144

1889 27, 926

1890 9,335

Short tons.

1891 1,064

1892 26,000

1893 10,000

1894 No report.

7,943 16, 413 15, 517 10,409

The McFerran mine commenced producing in November, 1888.* In 1896 it was abandoned and the inspector says: ''It appears that the mine has never been on a paying basis." A table of its production follows:

Production of McFerran coal mine, 1888-1896.

Short tons.

1893 19,318

1894 No report.

1895 41,995

1896 8,424

Short tons.

1888 5, 000

1889 26, 140

1890 17, 512

1891 33, 300

1892 9, 788

Until 1896 the McFerran and Franceville mines were the only ones reported for El Paso County by the state inspector. About that year, apparently, several small mines were opened in the west end of

o Mineral Resources U. S. for 1882. U. S. Qeol. Survey, 1883, p. 39 Third Bienn. Rept. Colorado State Coal-Mine Insp.. p. 104. c Seventh Bienn. Rept. Colorado State Coal-Mine Insp., p. 36.

340 Contributions To Economic Geology, 1908, Pabt U.

the field — that is, north of Colorado Springs — only to be abandoned within the next year or two. Of the present larger mines north of the town the Carlton or Pikeview was the first to be opened. Shaft sinking was begun in the latter part of 1896 and the main coal was struck January 1, 1897."

The Curtis, Danville, and Williamsville mines followed within the next year, and others, some of them now abandoned, were opened from time to time thereafter.

The principal developments at present are the group of mines about 2 miles north of Colorado Springs. Of these only the Curtis and Rapson have shafts, the others being slope mines. The room and pillar method of extracting the coal is used entirely, with pillars about 18 feet thick and rooms about 22 feet wide.. Some coal is almost always left in the roof because the rock overlying the coal is in most places a very weak sandy clay. As the coal in these mines is of good quality and abundant to meet present demands, there has been no effort to develop the deeper-lying portions of the bed. The depth of the Carlton or Pikeview shaft, the deepest in the field, is 175 feet.

The Neer mine is also opened by a shaft and is working on about 3 feet of coal believed to be coal A.

On coal B the only mine now operating is the Monument Valley, in the SW. sec. 11, T. 13 S., R. 67 W., near the south line of the section. This mine differs from all the others in that the bed dips steeply, and hence the slope starts directly on the coal. It was reopened so near the end of the field season that there was no time to examine the deeper workings. At the mouth of the slope the coal is about 3 fet thick; in depth, 4 feet of it is reported.

The only mines operating farther east are the Cell, or new Franceville, and the Davies mine, in the southwestern part of T. 14 S., R. 64 W. Both of these are slope mines with about to 4 feet of coal.

The coal of the Colorado Springs field is used largely for domestic purposes. It soems in addition to be very satisfactory for burning under boilers, as it is applied in this way by such plants as those of the Colorado Springs Electric Company and the mills in Colorado City and at Cripple Crock. The mines at Franceville supply a wagon trade entirely, for use mainly by creameries and ranches.

Any part of the field can be easily entered by a railroad; in fact, there were branches to the old Franceville and McFerran mines while they were still operating.

o Eighth Bicnu. Rept. Colorado State Coal-Mine Insp., p. 74.

The Canon City Coal Field, Colorado.

By Chester W. Washbubne.

Introduction.

The Canon City coal field is located on the east front of the Rocky Mountains in south-central Colorado. It is one of the earliest developed coal fields of the State and is one of the best known, producing a high-grade, clean, dry domestic fuel.

The following paper sums up briefly the principal results of a reconnaissance examination made in the summer of 1908. Many of the east-west section lines were traversed on foot, distance being determined by pacing and points located by compass intersections. The outcrops of the coal beds were jneandered in the same way, and sections of the beds were made in the mines and prospects, it being impossible to measure the coal elsewhere. The original purpose of the work was land classification, and when it was ascertained that no coal land remained in possession of the Government no attempt was made to dig into the weathered outcrops to measure the coal beds, and only such data were gathered as seemed most useful to those engaged in prospecting or developing the field. No attempt was made to sketch the topography. The more detailed results of this work will be presented in a later pubUcation.

Topography.

The Canon City coal field occupies a small mesa at the foot of Weft Mountain and west of a broad valley of Pierre shale, in which lies the Florence oil field. The mesa rises gradually westward in smooth grassy plains that merge with Wet Mountain in the southern part of the coal field. In the. northern part of the field there is a depression in the mesa, known as Wolf Park, west of which is a sharp ridge of the upturned sandstone of the Laramie formation separating this park from the shale valley that lies at the foot of Wet Mountain. The north and east sides of the coal field are marked by a series of high cliffs characterized by projecting points and deep reentrants. The latter were cut by small creeks, most of which are intermittent in flow, but Newland, Oak, and Chandler creeks, which rise in Wet Mountain, carry a perennial flow across the coal field.

342 Contbibutions To Economic Geology, 1908, Pabt H.

Small pine and oak trees grow over most of the northern part of the mesa and along the stream courses in the southern part. These are not suitable for mine timber, and consequently material for this purpose must either be hauled by wagon from Wet Mountain or shipped by rail from distant places. There is a good growth of grass on the mesa which is green for the greater part of the year. The principal wagon roads across the field follow the sharp canyons. Elsewhere travel is difficult, owing to the abundance of small guUies and cliffs.

Spurs from the Denver and Rio Grande and the Atchison, Topeka and Santa Fe railroads reach all the principal mines in the northern and eastern parts of the field. The southwestern part has no railroad connection and therefore no important mines.

General Geology.

Structure.

Throughout the greater part of the coal field the strata dip gently westward at angles varying from 2® to 5°. Along the western margin the strata are sharply upturned, probably from the influence of a thrust fault at the foot of Wet Mountain. This fault cuts across the coal measures in the southerii part of the field and is marked by a complete overturn of the beds in that locality. (See PI. XVIII.) The coal beds are there overlain by granite which has been thrust upon them. On tracing the coal beds northward from the granite contact they are seen to be overturned, having westward dips of about 45° for a distance of over a mile; farther north they are upright for several miles and acquire progressively lower eastward dips as they leave the influence of the Wet Mountain fault. At the northwest end of the field, where, owing to its distance, the influence of the fault is slight, the dips are only 12° to 20°. The structural features are best shown by the dip symbols on the accompanying map (PL XVIII).

Stratigraphy.

The coal beds of the Canon City field occur in the Laramie formation. Beneath the Laramie is the Trinidad sandstone, which rests on Pierre shale. Various Mesozoic and Paleozoic strata he between the Pierre shale and the Archean granite, but these have no economic bearing on the coal field and therefore will not be described in tliis paper. Above the Laramie is conglomerate, probably equivalent to the Arapahoe conglomerate of the Denver Basin and the Poison Canyon formation of the Trinidad field. A small remnant of tuflFaceous sandstone and shale, probably corresponding with a part of the Denver formation, rests at one locahty on the Arapahoe (?) conglomerate.

Canon City Coal Field, Colorado. 343

Pierre Shale.

The Pierre shale is a remarkably uniform body of consoUdated sea mud, soft dark gray to greenish black at the surface of the ground. The fresh unweathered shale is firm and readily fissUe along the bedding planes, as shown by the fiat platy character of the drillings from oil wells. Considerable bodies of it are almost white, although dark-gray to bluish-black colors prevail. It contains numerous large, hard calcareous concretions, a few of which make ''tepee buttes" on the low plains north and east of the coal field. Small hard, brittle ferrocalcareous concretions are abundant at certain horizons. In grading a street in the western part of Florence a bed of bluish-white limestone, about 2 inches thick, was observed, but this is the only occurrence of limestone in the upper part of the Pierre shale observed in this region. Near the base of the shale are a few nonpersistent beds of very impure limestone 1 to 8 inches thick. Beds of sandstone 6 inches to 3 feet thick are common in the upper 300 feet, and in this zone there are in most sections one or two beds of resistant sandstone 5 to 10 feet thick. A few thin beds of sandstone are found as far as 700 feet below the top of the Pierre, but there are none below that horizon. As the base of the overlying Trinidad sandstone is approached, sand and clay become equally important constituents of the section and are distributed in a pecuUar and interesting way. Beds of sandstone 4 to 8 inches thick alternate with beds of shale 2 to 6 inches thick, through a distance of 30 to 50 feet below the base of the Trinidad sandstone. This regular alternation of coarse and fine sediment is suggestive of the work of periodic floods alternating with slower currents at the mouth of a river. At one locality fifty-two of these beds of sandstone separated by partings of shale were counted in a section 45 feet thick. The beds contain no fossils on the east side of the field, but on the west side the leaves of deciduous plants are abundant in both the sandstone and the shale. At different horizons in the underlying shale are found many marine Upper Cretaceous bivalves and ammonites.

Trinidad Sandstone.

The Trinidad sandstone is a massive, yellow-weathering sandstone, thin bedded near the base, where it grades imperceptibly into the Pierre shale. Layers of clay become increasingly abundant toward the bottom of the sandstone, and in the upper part of the shale layers of sandstone become increasingly abundant toward the top. The boundary between the two is uncertain, and the base of the former in the Canon City field may not correspond exactly with the base of the Trinidad sandstone in the Trinidad field. In the latter locality the top of the Pierre shale contains invertebrate fossils of the

344 Contributions To Economic Geology, 1908, Part Xl.

same types as those found at the same horizon near Canon City. Moreover, the name Trinidad sandstone is now well established in this field, because both geologists and miners have observed the Uthologic similarity between the sandstone at the base of the coalbearing strata at Trinidad and the sandstone at the base of the coalbearing strata of the Canon City field. The continued use of the name Trinidad sandstone therefore seems preferable to the introduction of a new name, although it must be admitted that the sandstones may not be precisely synchronous deposits.

As recognized in this field the Trinidad sandstone ranges from 50 to 100 feet in thickness and includes only the massive sandstone beneath the Rockvale coal bed. For about 50 feet below it sandstone and shale are present in nearly equal amounts, and, as already mentioned, the upper 300 feet of the Pierre shale is very sandy. As the base of the Trinidad sandstone is not a sharp line, other observers might prefer to place it as much as 300 feet or more below the Rockvale coal, thus including sandstones and sandy shales which the writer has considered merely sandy members of the Pierre shale.

No fossils were found in the Trinidad sandstone, not even the peculiar lozenge-pattern prints of the marine plant often called fossil corncobs (Halymenites major), which is elsewhere so characteristic of this sandstone. The search for fossils in the Trinidad was not thorough, yet was sufficient to show that Halymenites is either absent or at least rare in the Trinidad at Canon City, although in a yellow sandstone in the coal measures about 300 feet above the Trinidad this fossil is very abundant. The sandstone is more massive and, in places, strongly cross-bedded on the west side of the coal field, suggesting that Wet Mountain was land and that the Canon City embayment was occupied by the sea at the time the Trinidad sandstone was deposited.

Laramie Formation.

The Laramie formation, which contains all the coal beds of the Canon City field, rests conformably on the Trinidad sandstone and is unconforniably overlain b}" the Arapahoe (?) conglomerate. The productive division of the formation is the lower 600 to 700 feet, consisting of sandstone and dark-colored, usually carbonaceous shale. On the east side of the field the third of the productive division consists mainly of sandstoiK* and the upper two-thirds mainly of shale, hut on the west side sandstone predominates over shale in all parts of this division. Overlying the productive division is a resistant, massive sandstone about 250 feet thick, which is a controlling factor in the topography, producing a sharp ridge where it stands vertical along the western margin of the field and causing the high escarpment of nearly horizontal coal-bearing strata which it caps on

CANON CITY COAIi FIELD, COLORADO. 345

[le east side of the field. Above the resistant sandstone at Alkali rap there is 255 feet of soft yellow sandstone in beds 2 to 5 feet thick 3parated by sandy shale and probably by some dark carbonaceous lale, but over the greater part of the field this, the highest member f the Laramie formation, is absent and the Arapahoe ( t) conglomrate rests directly on the underlying thick massive sandstone. The iiaracter of the formation in the western part of the field is shown 7 the following detailed section of the rocks, which was measured y C, A. Fisher and the writer with a steel tape.

Section of rocks in Alkali Gap.

Sandstone, tuffaceous, and bright colored clay, probably Ft. in. Denver formation, nearly horizontal 50

Not exposed, horizontal distance 325 feet, dip unknown ?

Sandstone, mostly, with layers of conglomerate, dip 75® E 160

Not exposed, soft, probably dark shale 60

Conglomerate 260

Total exposed Arapahoe (?) o 480+

Unconformity.

Sandstone, soft, with streaks of sandy shale, nearly vertical 255

Sandstone, strong, massive, makes crest of ridge 250

Not exposed, probably mostly soft sandstone, some fire clay

at top 40

Coal, thin bed.

Sandstone 25

Not exposed, soft rocks 20

Coal, probably Brookeide bed 3

Shale 2

Sandstone, white, even bedded 20

Sandstone, soft 35

Not exposed 30

Coal, in black shale 1 6

Not exposed 20

Sandstone, with fossil leaves at base 55

Coal, Chandler bed, in an open cut 4-5

Sandstone and shale 40

Coal, top not exposed 1+

Sandstone, coarse grained, massive, with iron concretions,

weathers yellow 65

Sandstone, shaly 30

Coal, upper Royal Gorge bed 4

Shale, hard, sandy 10

Coal, bloom, lower Royal Gorge bed 4

Sandstone, soft, white 27

Shale, with coaly streaks 5

In the Littell shaft, 1 mile east of Alkali Qap, the thickness of the Arapalioe (7) is about 550 feet. Measarement obtained in the Royal Oorge mine. The lower bed can not be measured In Alkali Oap thout considerable digging.

"fvW.

346 CONTBIBUTIONS TO ECONOMIC GEOLOOT, 1908, FABT n.

Ft. In.

Sandstone, soft, gray 31

Coal, 2 feet Coal Shale, 1 foo Coal, 1 foot

Not well exposed, probably mostly shale 41

Sandstone, hard 8

Not well exposed, mostly shale 52

Coal 2 6

Sandstone and shale, with a non workable bed of coal near base . 63

Coal ?

Sandstone 15

Coal ?

Shale 25

rCoal, Ifoot 1

Coaljshale, 1 foot [Nonac bed 3 8

[Coal, 1 foot 8 inches]

Sandstone, coarse, white 50

Coal, Rockvalebed 2-6

Total Laramie 1,242

Sandstone, Trinidad 55

Shale, blue, sandy 45

Sandstone 1

Shale 5

Sandstone, massive 8

Shale, blue, sandy, with thin partings of sandstone 40

Shale, sandy, yellow, containing large concretions with

Pierre fossils 45

Shale, blue, sandy, with concretions 65

Sandstone, soft, shaly 4

Shale, sandy, blue, yellow, white 50

Shale, blue, containing at base concretions with Lucina ocd-

dentalis 250

Shale, blue-black, with thin indurated sandy layers containing comminuted plant fragment*s 150

Shale, clayey, dark, slickensided 3, 000

ToUl Pierre and Trinidad 3,718

Fault. Granite.

Coal is present only in the lower 600 feet of the Laramie formation, the overlying sandstones barren in this field.

The rocks of the Laramie formation become much finer in grain toward the east side of the coal field. This change is especially noticeable in the upper part of the productive division, which consists principally of shale in the eastern part of the field and largely of sandstone in the western part, although there is considerable shale at the west also, as shown by the section in Alkali Gap given above. For

a The entire thickness of the Pierre shale Is not present at this locality. In the Florence oil field it mee9> ures about 4,500 feet. See p. 519.

CANON CITY COAIi FlELDj COLOBADO. 347

comparison with the Alkali Gap section, the following measurements )f the strata exposed in the bluff north of Rockvale may be of interest.

Section of part of the Laramie formation on the hiihide north of Rockvale,

Ft. In.

Sandstone, maasive, probably part of the big barren aandstone. . 25

Not exposed 15

Coal, blossom ?

Shale 25

Sandstone 10

Shale 25

Coal, sure measurement 2

Shale, dark, with three 1-foot beds of sandstone 25

Coal, surface measurement 6

Shale, dark 35

Sandstone, soft, and sandy shale 5

Sandstone, strong, thin bedded, fine grained 6

Coal, blossom, thickness probably 1

Shale, mostly dark colored, with streaks of coal 45

Sandstone, shaly , 8

Shale 4

Sandstone 5

Shale, carbonaceous 15

Sandstone, soft, with layers of firm white shale 5

Shale, dark, carbonaceous 12

Sandstone, resistant 10

Shale, dark 13

Coal 2

Clay 2

Coal, surface measurement 1

Bone 1

Sandstone, soft, coarse grained, white, with brown ironstone

concretions 8

Shale 5

Sandstone 6

Shale, black, carbonaceous, with many black clay-ironstone

concretions 25

Sandstone and shale, soft 4

Coal, BXirisLce measurement 1

Shale, sandy, weathering white 20

Shale, black, carbonaceous 25

Sandstone, massive 10

Shale, carbonaceous 15

Sandstone, strong, with gnarly brown concretions at top 12

Shale, sandy 5

Sandstones, massive 8

Coal, surface measurement 2 2

Shale, carbonaceous and sandy 10

Not exposed, rock beneath the valley 350±

794 6

348 CONTBIBUTIONS TO ECONOMIC GEOLOGY, 1908, PAfiT tl.

The lower two-thirds of the concealed strata at the base of this section was measured near the Bluff Springs mine and a section of the rocks will be found on page 355. F. H. Knowlton reports that the upper part of the coal measures contains a flora equivalent to that of the Laramie formation of the Denver Basin, but that the lower part contains a flora of upper Montana age. According to the original definition of the Laramie by which the term includes the coal-bearing strata resting conformably on the top of the marine Cretaceous, there seems to be no good reason for separating these lower beds from the Laramie even though they contain an upper Montana flora. There is no noticeable lithologic change within the coal-bearing strata that can furnish a satisfactory basis of subdivision into a Laramie and an upper Montana formation, except on the eastern edge of the field north of Radiant, where a yellow thin-bedded sandstone 40 to 70 feet thick contains many impressions of Halymenites major, a marine plant. Knowlton reports that this sandstone separates the strata containing an upper Montana flora from the overljdng beds, which contain a flora similar to the Laramie. When the sandstone is traced toward the mountains either southward beyond Radiant or westward to the west side of the field, it is seen to lose its marine character, its thin bedding, fossils, etc., and to become massive, coarse grained, and cross-bedded, acquiring all the characters of a fluviatile sandstone. On the west side of the field it is impossible to distinguish this sandstone from others above and below it, except by careful comparison of detailed sections, and it therefore has little value as a horizon marker in that region.

The lithologic succession in this field is almost precisely identical with that at Denver, and the writer therefore does not hesitate to correlate the strata of the Canon City coal field with those of the Denver Basin, admitting that on paleobotanic evidence the lower coal beds may be somewhat older than the lowest coal at Denver.

Arapahoe (?) Conglomerate.

The Arapahoe (?) conglomerate rests unconformably on the sandstone at the top of the Laramie formation. In the Alkali Gap section (see p. 345), the conglomerate rests on a soft, distinctly bedded sandstone with layers of sand v shale, which measures 255 feet in thickness. This sandstone thins out northward, on account of pre- Arapahoe erosion, and half a mile north of Alkali Gap, opposite the Royal Gorge coal mine, the conf];l()morale lies directly on the lower resistant massive sandstone, which there measures about 235 feet in thickness. Apparently erosion had cut about 270 feet deeper in the rocks at the latter locality than it had at Alkali Gap before the deposition of the conglomerate. Over the whole of the Canon City field, except at

Canon City Coal Field, Colorado. 349

Alkali Gap, the conglomerate rests on the resistant massive sandstone, and the overlying soft sandstone is absent. At the gap the soft sandstone was presumably in some way protected from erosion.

As the Arapahoe (?) conglomerate lies unconformably on the Laramie it is not surprising that a few fragments of sandstone and coal of the Laramie are present in the conglomerate. Fragments of Pierre shale were not seen in the conglomerate, but the Niobrara and Paleozoic Umestones and cherts and the Dakota (?) sandstone are represented by a few pebbles, and one fragment of Ordovician sandstone containing a fish scale was found. Small waterwom pieces of red sandstone from the "Red Beds" and rounded quartzite pebbles from an unknown source are abundant. Pebbles of all these rocks, however, are greatly outnumbered by those of Archean granite, granite gneiss, schist, quartz, and coarse-grained igneous rocks that intruded the Archean complex in pre-Ordovician time. The lastnamed rocks are common in Wet Mountain and all the sedimentary rocks which compose the minor part of the Arapahoe (?) conglomerate are found upturned along the front of the mountain, except that there is no quartzite like that of the pebbles. Diligent search failed to reveal any pebbles of effusive igneous lava or tuff such as characterize the Denver formation, but pebbles of coarse-grained porphyries are numerous, being probably derived from pre-Ordovician intrusions in the Archean complex. Granite pebbles and small pieces of granitic quartz and feldspar are by far the moat abundant constituents of the conglomerate. Although the pebbles of sedimentary rock seem to be most plentiful in certain layers near the middle of the formation, there is essentially no difference in the materials of the conglomerate from bottom to top.

In Alkali Gap the lower 260 feet of the Arapahoe ( ?) is pure conglomerate with very little sand. It outcrops in massive beds about 20 feet thick. The basal bed contains the largest pebbles, which range from 3 to 10 inches in diameter and are mostly subangular but slightly waterworn. The rare quartzite pebbles, however, are all well rounded and smooth. Above the massive conglomerate are 60 feet of poorly exposed strata, probably soft sandstone or sandy shale, and some dark carbonaceous shale, seen only in the d6bris of rodent holes. In the succeeding 160 feet of strata there are four beds of pebbly sandstone, each about 10 feet thick, separated by intervals of 30 to 40 feet in which the rock is not exposed. To judge from the soil, the d6bris of prairie-dog holes, etc., these intervals in which the rock is not exposed are occupied by coarse sandstone, possibly with pebbly layers. The pebbles in the sandstone beds are mostly in layers 6 to 18 inches thick. They are similar in material to those in the underlying conglomerate, but are smaller, one-fourth inch to 1 inch in diameter, and more nearly rounded. Quartz pebbles are more abviw-

850 Contributions To Economic Geology, 1908, Fabt H.

dant in the upper layers than in the massive conglomate. These are the highest beds of the Arapahoe (t) conglomerate observed in the Canon City field. They dip 76° to 86° E. The succeeding interval, across 326 feet of ground, contains no exposures. The next exposure is that of beds of the Denver ( ?) formation lying horizontally. If the concealed rocks stand nearly vertical in this interval, they are about 325 feet thick, but it is probable that the dip is less steep and consequently that the thickness is much less than 326 feet, perhaps about 70 to 100 feet, for the total thickness of the Arapahoe (?) in the Littell shaft, about one-fourth mile east of this locality, is only 650 feet, the lower 480 feet of which has already been described as occurring at Alkali Gap, leaving only 70 feet to be accounted for. It is in this interval that the beds change abruptly from a nearly horizontal to a nearly vertical position.

The Arapahoe ( ?) conglomerate underlies the whole of Wolf Park, extending at least as far south as Chandler. Along the wagon road between Canon City and Chandler the conglomerate is well exposed on some high lulls, where it dips northwestward at a low angle. In the southern part of the field it lies along the axis of the syncline, which is west of the center of the field. Its eastern margin can not be observed in the southern area, and its position as shown on the accompanying map (PL XVIII) is largely conjectural.

The Arapahoe ( ?) is very different from the underlying formations in the character and coarseness of its material. The presence of material from these formations in its pebbles indicates that a long period of erosion preceded the deposition of the conglomerate. The fact that it was involved in the last great orographic movements of the Rocky Mountains prevents the possibility of confusing it with late Tertiary gravel. The writer follows Eldridge, Hills, and others in correlating this formation with the Arapahoe of the Denver Basin.

Denver (?) Formation.

At a distance of 325 feet east of the last exposure of Arapahoe (?) conglomerate in Alkali Gap the small creek that flows through the gap has undercut a few feet of green and red clays containing thin beds of brown and yellow sandstone with pebbly layers. The beds lie nearly flat, dipping not more than 3° or 4° E., but this does not indicate that they have not been involved in the folding of the lower formations. The structure makes it highly probable that the lower formations are also nearly horizontal at this locality. The exposure is imperfect. There is no indication of the existence of more than 50 feet of rocks assignable to this formation, yet from the presence of tuffaceous and andesitic material in the pebbles first reported by Eldridge, it seems best to follow him in considering the exposure a probable small remnant of the Denver formation. The rocks should

Canon City Coal Field, Colorado. 351

be separated from the Arapahoe ( ?) conglomerate because of the presence of the distinctive andesite and red and green clays. There is no evidence of the existence of more than 1 acre of Denver ( ?) rocks, but more may be concealed beneath the valley wash on the west side of Wolf Park, outside of which it is not possible for any Denver ( ?) strata to be left in this region.

The Coal.

STRATlGRAPmC POSmON OF COAL BEDS.

As mentioned above, all the workable coal beds are in the Laramie formation. Indications of coal have been found in the Dakota sandstone, but as a rule the beds are thin and apparently of no value. (See p. 371.)

The correlation of coal beds which can not be accurately traced on the surface is not an easy matter; nevertheless the approximate position of any bed may be determined by geologic methods without serious error. In the following table the endeavor is made to project all the known coal beds on a section of the Laramie formation measured near Rockvale, for the purpose of showing the relative position of the beds. Some generalization has been necessary on account of differences in thickness of the beds away from the Rockvale section, and because not all of the coal beds are present in that section. The coal of many of the horizons can not be traced from one mine to another, and it is known that some of the coals are not continuous between mines that work beds at probably the same horizon.

Section of the Laramie formation in Canon City coal field y Colorado , showing the relative

positions of the coal beds.

Unconfonnity at the base of the Arapahoe (?) conglomerate. Feet.

Sandstone, resistant 250-500

Sandstone, soft, and shale, with thin coal beds 125

Horizon of the coal bed of the Brookside and Brilliant mines. Interval, mostly sandstone, with thin coals 75-165

Horizon of the coal bed of the Chandler and Littcll mines and of the Simons prospect in Alkali Gap. Interval, mostly sandstone 95-135

Horizon of the Royal Gorge coal beds and possibly of the Bassick bed. Interval, mostly sandstone 70

Horizon of the Radiant coal bed. Interval, mostly shale 75-100

Horizon of the coal of the Ocean Wave or Magnet mine. Interval, sandstone and shale, with thin beds of coal 100-115

'BLonx/om at the coal of the Nonac and Diamond mines. Sandstone 30-50

Horizon of the coal of the Fremont, Rockvale, Coal Creek, and Blufif Springs mines. This coal bed is considered the base of the Laramie formation. Trinidad sandstone,

352 CONTRIBUTIONS TO ECONOMIC GEOLOGY, IJOSj PABT n.

Description Of Mines And Prospects.

RocJcvale mine, — The Rockvale mine is the largest in the Canon City field, producing an average of 850 to 900 tons a day and at times over 1,000 tons a day. The mine is about thirty-five years old, having been first opened by the Santa Fe Railway Company from a shaft (Santa Fe No. 4), located one-half mile northeast of the present Rockvale shaft, which was completed by the Colorado Coal and Iron Company in 1881. The mine is operated by the latter company, reorganized under the name Colorado Fuel and Iron Company.

The Rockvale mine is in the lowest bed in the field and its workings merge and intercommunicate with those of the Fremont and Coal Creek mines, both of which are also operated and owned by the Colorado Fuel and Iron Company. The coal is hoisted by steam powor through a two-compartment shaft 323 feet deep, the top of which coincides with the upper surface of the yellow sandstone, which here contains abundant impressions of Halymenites. The coal is dumped from a wooden tipple over screens directly into coal cars, most of the lump coal being loaded into box cars by a steel box-car loader operated by electricity. The fine coal is washed but does not find a readj market, and in 1908 a large amoimt of slack was piled beside the railroad track.

The coal bed rests on the Trinidad sandstone at the base of the Laramie formation. In the Rockvale mine it slopes westward from 6 to 6i per cent and varies in tliickness from 3 feet 4 inches to 4 feet, the thicker coal invariably being overlain by ''draw slate'' and the thinner coal usually by sandstone. This relation prevails throughout the three ad j aeon t mines, Fremont, Rockvale, and Coal Creek, and is probably due to the erosion of the original clay and of the top of the original peat, wliich were consolidated to the ''draw slate*' and the coal, respectively. The erosion is supposed to have been effected by the swifter current that deposited the sand of the overlying sandstone. By platting the position of the places where the sandstone roof comes in contact with the coal in the three mines, significant relations Jiave discovered between the character of the coal beds, especially in regard to roof and partings, and the position of the stream channels in the swamps of the coal-forming period. The main stream channel as thus located lies just north of the Fremont workings, in the northern part of which the coal is of Uttle value on account of partings. These relations will be fully discussed in the final report.

Mining is done wholly by hand in the Rockvale mine, the long-wall method being followed. The distribution of joints in the coal makes driving easiest in a northeast or southwest direction. In the first entry north of the C dip slope off the main south slope the butts trend N. 40° E. and the faces N. 50° W. The butts are 2 to 8 inches

CANON CITY COALr FIELD, COLORADO. 353

apart, with an average of about 5 inches; the faces are strongly developed and the distance between them varies from 1 to 4 inches, averaging about 3 inches. Tlie joints appear to be of the same general character wherever examined in this mine. In the fourth entry south of the C dip slope off the main south slope the butts trend N. E. and are spaced 2 to 12 inches, with an average of about 6 inches; the faces trend N. 50° W. and are spaced 1 to 3 inches, with an average of about inches.

The coal breaks down in lumps 1 to 3 feet across, with considerable quantities of finer dfibris. It is reported that in this mine, as well as in most of the other mines, the introduction of foreign workmen as a result of labor troubles in recent years has caused a marked falling off in the percentage of lump coal produced and in the general eflSciency of the working force. As the Canon City coal is mined principally for domestic use, for which it commands a high price, the percentage of lump coal is an important factor in mine management.

In the Rockvale mine the coal cars are hauled by mules to the main slope, where they are attached to a cable and drawn by electric drums to the foot of the shaft. Gas is not abundant and the small amount present appears to come mainly from the coal and only in part from the roof.

Fremont mine. — The Fremont mine is on the same coal bed as the Rockvale mine and the workings of the two intercommunicate underground. The shaft of the Fremont is located about miles northwest of the Rockvale. The Fremont mine is operated by the Colorado Fuel and Iron Company and produces about 400 tons of coal a day in the following proportions: Lump coal, passing over 3-inch perforated shaker screen, 50-51 per cent; nut coal, 22-23 per cent; slack and pea coal, 21-22 per cent.

The shaft is 402 feet deep and is equipped with a hoist of 100 horsepower, steel top frame, and self-dumping cages handling about 75 cars an hour. The tipple is also built of steel and has a steam box-car loader and shaker screens. The trips of coal cars are hauled to the foot of the shaft by a 75-horsepower electric traction motor. Water is pumped by two small electric pumps from the working faces to a sump at the foot of the main shaft, whence it is raised to the surface by a 75-horsepower electric pump working two hours a day at a rate of 50 gallons a minute. In 1908 about 180 men were employed underground and 35 at the surface. The miners receive 85 cents a ton for hand mining.

The coal bed has an average thickness of about 4 feet, ranging from 3 feet to 3 feet 6 inches under the sandstone cap rock and from 4 feet 6 inches to 5 feet under shale. Sandstone comes into contact with the coal in the southeastern part of the mine, but in most other parts the cap rock is shale. The line of separation between the areas of

TOOa**— Bull. 381—10 23

354 Contributions To Economic Geology, 1908, Pabt Ii.

sandstone and of shale cap rocks trends in a general northeast-southwest direction, running about 1,000 feet south of the shaft and continuing into the Rockvale mine. Southeast of this line the cap rock is sandstone in most places. Northwest of the line the cap rock is sandstone only where rolls or similar irregularities permit it to descend through the shale, which varies from 1 to 7 feet in thickness.

Joints are well developed in this mine. The butts trend N. E. and are about three-fourths of an inch apart; the faces trend N. 50° W. and are half an inch to inches apart.

Coed Creek mine. — The Coal Creek mine of the Colorado Fuel and Iron Company is located in sec. 31, T. 19 S., R. 69 W., and ships its product over a spur of the Denver and Rio Grande Railroad running 3 miles northeastward to Florence. The mine is worked by a slope which now extends about a mile west of the entrance and has a dip of about 3°. It was first operated from a slope that lies threefourths of a mile north of the present location and is commonly known as the old Coal Creek slope or the Canfield mine. The Coal Creek mine was not entered by the writer because of its proximity to the Rockvale and Bluff Springs mines, which work the same coal bed at the base of the Laramie formation.

The mine maps kindly furnished by the Colorado Fuel and Iron Company show that the thickness of the coal bed near the center of the SW. i sec. 31, T. 19 S., K. 69 W., is 3 feet 3 inches, and one-fourth mile north of the southwest corner of sec. 31, T. 19 S., R. 69 W., 3 feet 6 inches.

Seven feet above the Rockvale bed at Coal Creek there is about a foot of coal which persistently accompanies the Rockvale bed in tliis part of the field. Its distance from the Rockvale bed increases toward the north to 10 feet in the Rockvale mine and to 15 feet in the Fremont mine. In the southwestern part of the Coal Creek mine the intervening rock, principally sandstone, which separates the top coal from the main bed, wedges out and permits the top coal to rest on the main bed with only a trace of separating clay.

The mining ()[)erations at Coal Creek are similar to those at Rockvale, the long-wall method being used exclusive}-. The production is somewliat smaller than that at Rockvale, owing largely to the fact that a slope is slower to operate than a shaft. Mining at Coal Creek is facilitated by the ease with which the coal breaks from the roof, owing to an intervening thin parting of argillaceous rock. In most parts of the Rockvale mine the cap rock is frozen'' to the coal, making clean extraction of the coal somewhat diflicult.

Bluf Springs mine. — The Bluff Springs mine, locally known as the Blazing Rag, is a small mine now operated by J. T. McLean, of Florence, and located about 2 miles southwest of the town of Coal Creek. Its output, which is small, is hauled by wagon to Florence and neigh-

Canon City Coal Field, Colorado. 355

boring towns. This is the most southerly mine working the Rockvale coal bed, which becomes thin farther south. The coal bed varies in thickness from 3 feet to 3 feet 6 inches in the Bluflf Springs mine, including a clay parting 1 to 3 inches thick near the middle of the bed. The clay parting thickens southward to 18 inches at a distance of 2,000 feet from the shaft, the upper bench of coal becoming correspondingly thinner and more dirty until it disappears about half a mile south of the shaft. The lower bench continues with varying thickness at least as far as Radiant, where it is reported to be about 3 feet thick in an old prospect shaft near the tipple of the Radiant mine.

Section of the lower part of the Laramie formation at the Bluff Springs mine.

Sandstone, yellow, with Halymenites major; the same bed that

outcrops at the top of the Rockvale shaft and back of Williams- Ft. In.

40

Not exposed 40

Shale, dark, carbonaceous 10

Coal a 2 2

Clay 4

Coal 6

Not exposed, probably mostly sandstone 10

Sandstone, white, massive 10

Sandstone, thin bedded 3

Coal; varies in near-by prospects from 1 foot 8 inches to 2

feet 4 inches 2

Rock not exposed, lying above the top of the air shaft 25

Gravel, recent wash at the top of the air shaft 15

Coal 7

Sandstone and shale 24

Coal 8

Shale and thin-bedded sandstone 10

Coal G-8

Shale 5

Sandstone 10

Coal 1 6

Sandstone, hard, concretionary 3

Shale, dark 12

Coal 1 6

Shale 2

Coal 1 8

226 7

The lower 80 feet of this section was measured in the new air shaft sunk in 1908. The rest of the section was measured on the surface.

Radiant mine, — The Radiant mine of the Victor Fuel Company is located in the western part of sec. 7, T. 20 S., R. 69 W. It is on a 3-foot coal bed whose position is estimated to be between 200 and 250 feet above the Rockvale bed, which is not workable near Radiant nor

At another prospect 700 feet north-northwest of the Blufl Springs mine this coal Is in one bench naeaauring 3 feet 10 inches in thickness.

356 Contbibutions To Economic Geology, 1908, Part H.

farther south. In the Radiant mine the thickness of the coal bed varies from 3 feet to 3 feet 9 inches. A section of the coal in the northern part of the mine is shown below:

Section of coal bed in the Radiant mine.

Shale. Ft. in.

Coal 1 4

Shale 0-2

Coal 1 11

Shale.

Mining machines are used to undercut the coal, which breaks free from the roof when shot except in the tenth north entry, where it does not part readily from the roof, or in the miner's phraseology, is '' frozen." ' The coal breaks down in long blocks 4 feet wide, 3 feet high, and sometimes 20 feet long when several holes are fired together. The blocks are usually 7 feet to 8 feet long for single shots.

Joints are strongly developed in the coal bed. The faces trend N. 47° W. and are from 1 to IJ inches apart. The butts trend N. 50° E. and are IJ to 3 inches apart. In the tenth north entry there is rude columnar jointing at the top of the coal bed. The columns are about 2 inches across and penetrate the coal for about 6 inches. They are very irregular in cross section. The origin of these joints is not known, but they are possibly due to weathering, although the coal is about 100 feet below tlie surface in this entry. No igneous intrusions have been noticed in this neighborhood.

Mining operations in the Radiant mine follow a combination of rooni-and-pillar and long-wall systems. The room-and-pillar method is used for a short distance on either side of the main slope, beyond which the coal is removed by the long-wall method. The coal is all undercut with electric machines, the mine being equipped with five Sullivan long-wall machines and one Jeffrey chain-breast machine. The machine men receive 7 cents a linear foot for undercutting. The loaders are ])aid 45 cents a ton. After the coal is loaded the mine cars are pushed to the main slope and there hooked to a cable that is drawn by an electric drum to the tipple, about one-fourth mile east of the mine moutii. The tipple is equipped with a steel automatic dump and shaker screens. It has one Westinghouse box-car loader. In the mine there is very little gas, and safety lamps have never been needed. Good ventilation is secured by a furnace at the foot of an air shaft in tiie southern part of the mine.

The coal ap[)ears to be softer and breaks much more easil} than that in the northern part of the field. It also slacks more rapidly. Lump coal that had been ])iled in the open air at the Radiant mine for about three montlis in 190S had begun to slack so that the miners reported that only about half of the original amount of lump coal

CANON CITY COALr FIELD, COLORADO. 357

could be obtained from the pile. The weathering of these lumps makes the cubical cleavage much more prominent than it is in the fresh coal. As many as six or eight strong joints to the inch appear. In the fresh coal the cubical cleavage can scarcely be distinguished.

The coal bed has an average westward dip of about 2° 15'. In the lower part of the mine the dip is in general about 2° and in the upper part about 3°, but there is much variation, produced apparently by broad open folds or ''rolls'' in the coal bed. These rolls cause alternate changes in dip of only about 1°, yet they are very noticeable on traveling up the slope. The dip at the end of the slope in 1908 was W. In passing eastward from this point up the slope, dips of 1°, 3°, 2°, and 3° were successively encountered. As in all the rest of the eastern margin of the coal field, the coal bed dips most steeply at the mouth of the mine. This steepening of the dip near the outcrop is probably due to the weathering and expansion of the underlying beds, which are principally shale. It is very noticeable in the southern part of the field, where it is clearly not due to folding, because the line of steeper dips follows the front of the mesa, running up the gullies and around the points with the outcrop of the coal bed.

Shaw prospect. — A small amount of coal has been taken from a slope running eastward on the Radiant bed about one-fourth mile south of the Radiant mine. The entrance to this slope is on the east side of the creek that passes the entrance to the Radiant mine. Coal was hauled away by wagon previous to 1881, when the opening was closed. No further information about this prospect could be obtained at the time of the writer's visit.

BriUiant mine, — The Brilliant mine of the Diamond Coal Mining Company is located in sec. 25, T. 20 S., R. 70 W. It is operated by J. Walton and John D. Lloyd, of Canon City. The coal is hauled to Radiant by wagon and there loaded on railroad cars. The production is about 12 or 15 tons a day.

The coal bed, of which sections are given below, occurs in the upper part of the productive strata, probably at nearly the same horizon as the Brookside bed. It strikes N. 20° E. and dips 9° NW.

Sections of coal bed in the Brilliant mine. fltoctlOB 800 feet lontliWMt of foot of ihaf t. Section 100 feet southeast of foot of shaft.

Sandstone. Ft. in. Sandstone. Ft. in.

Shale 1 2 Shale 6

Coal, dirty 2-10 Bone

Coal 4 6 Coal 5i

' Bone 6

Coalhed 5 Shale 1

Coal 4 8

Coal, ."lightly bony 2

Coal bed G

358 Contributions To Economic Geology, 1908, Pabt U.

The "draw slate is removed in mining and the sandstone used as roof, which makes the rooms about 7 feet high. The top coal, 1 to 3 feet thick, is not quite clean but makes a satisfactory fuel for a steam boiler. In mining it is separated easily from the rest of the coal and is used in the operation of the mine. This top coal has a dull luster, doubtless due to its high ash content. (See analysis No. 6378, p. 374.) The rest of the coal bed, which varies in thickness from 4 feet 6 inches to 5 feet, is of a uniformly brilliant luster except for a number of dull layers, not over one-eighth of an inch thick.

The coal breaks readily along the bedding planes, a feature not observed elsewhere in this field. The faces trend N. 50° W. and are about 1 inch apart; the butts trend N. 30° E. and are 2 to 4 inches apart. Neither set appears to be very regular either in trend or in spacing.

The mine is operated by a small one-compartment shaft 96 feet deep, equipped with a steam hoist. A coal bed 2 feet 6 inches thick was penetrated by the shaft at a depth of 9 feet. The coal checks more rapidly in weathering than that of the mines in the northern part of the field. Although it does not keep quite so well as the lat ter, the coal of the Brilliant mine may be kept in stock several months without noticeable deterioration and is said to be a satisfactory domestic fuel.

Mountain mine. — The Mountain mine is a prospect shaft located near the middle of sec. 31, T. 20 S., R. 69 W. The mine is said to be completely raved in, having been idle for fifteen years, and therefore it was not visited. It is reported that about 9 feet of coal was present in this mine, the upper 2 feet being very dirty.

Chandler mine. — The Chandler mine of the Victor Fuel Company is located in the town of Chandler, near the southeast comer of sec. 22, T. 19 S., R. 70 W. It is on a coal bed, in the upper part of the Laramie formation, which lies from 75 to 100 feet below the Brookside bed and wliicli is probahl}'' equivalent to the coal at the bottom of the Littell shaft in sec. 16. Typical sections in the eastern and south-central parts of the mine are shown below:

of coal bed in Chandler mine.

South-central part.

Eastern part. SaiulstoilO. Ft. in.

0-3

Coal 4

iJone binder which doos not

hnak from coal 0

Coal 1 2

Coal bed 5 8

Ft. In. Shale.

Coal 3 6

Bono 1

Coal 1 4

Coal bed 4 11

Cakon City Coal Field, Colobado. 359

The local thinning out of the shale overlying the coal appears to be due mainly to a slight erosional unconformity of the sandstone roof. In most parts of the mine there are "sand rolls" or long lines along which the sandstone cuts down through the "draw slate" and into the imderlying coal. In places these sand rolls cut several feet into the coal and at one point a roll touches the bottom of the coal bed, the coal having been entirely removed at that point by erosion in the Laramie period. The sand rolls have round bottoms and curved sides, with no indication of sharp channeling. They trend northeastward in all parts of the mine. Some of them are several hundred yards long, but most of them are only a few hundred feet long. The width of the rolls varies from 10 to 30 feet. The shorter ones hang down in the workings of the mine very much Uke round-bottomed boats with broad ends. It seems probable that these sand rolls mark the position of stream channels that existed at a time immediately after the deposition of the "draw slate" over the coal. The crossbedding in the rolls indicates that the streams flowed in a general northeastward direction.

In the northern part of the mine several small faults have been encountered. In the eighth entry west from the main north slope there is a small fault trending N. 10° E. This fault has a downthrow of 4 to 5 feet on the east side. In the seventh entry west off the main north slope there is a small fault which trends east and west and is down thrown 3 feet on the north side.

The room-and-pillar system is used in the Chandler mine, the rooms being driven with widths of 30 to 45 feet. The shale roof clings to the overlying sandstone and the coal breaks sharply from the shale when shot. Very large blocks are shot down in mining as described on page 84. Most of the coal is undercut with Sullivan electric chain cutters. The miners receive $1.05 a ton for hand mining. The two men on the cutting machines receive 5 cents and 4 cents a linear foot. The loaders from the machines are paid 40 cents a ton.

Great Western mine, — The shaft of the former Great Western Coal Company, commonly known as the Cuckoo mine, is located almost. on the axis of the sharp flexure on the western margin of the field, in sec. 27, T. 19 S., R. 70 W. On account of this peculiar position with reference to the structure, the shaft penetrates horizontal rocks that are nearly vertical in the entries 300 to 470 feet west of it. In 1908 the mine was idle and in the hands of a receiver, but Mr. L. Lewis, who was temporarily in charge, kindly led the writer through the long crosscut that has been driven for 470 feet westward, across the strike of the upturned beds. The coal beds all appear to be considerably crushed by the upturning of the strata, and the condition of the tunnel was such that most of the rocks could not be satisfactorily measured without the expenditure of unwarranted time and risk of

360 GONTKIBUTIONS TO ECONOMIC GEOLOGY, 1908, PABT n.

accident. The stratigraphic section of the steeply inclined rocks in this crosscut is approximately as follows:

Section of strata in the old crosscut of the Cuckoo mine.

Ft. In.

Sandstone 50

Coal 1 5

Shale 2

Coal 1 10

Shale 2

Rock, mostly shale 50

Coal 1 6

Shale 1 1

Coal 2 1

Rock, mostly sandstone 25

Coal 2 3

Sandstone, with some shale 8

Coal 1 1

Shale, dark 70

Coal 1 11

Sandstone 10

Shale 5

Coal 1 2

Sandstone 5

Shale 20

Coal 3 2

Shale 4

Coal 5

Sandstone, with shale partings 30

Coal, badly crushed in shale, measuring 2 to 4 feet, average 2 6

Shale 15

313 2

The shaft penetrates the upper part of the same rocks, but the coal beds are thicker in the shaft, according to the following section, taken from a blueprint kindly furnished by Mr. C. L. Mitten, the company's engineer :

Section of strata in the shaft of the Cuckoo mine.

Ft. in.

Sandstone 157

Coal, average thickness 3

Rock, mostly sandstone 140

Coal 3 6

Rock, mostlv shale 29

Coal, average thickness G

338 6

This mine has a steam hoist, electric fan, and jnodorn tipple. It is connected by a short spur with the railroad track at Chandler. The mine has recently passed through a receiverehip and the new purchasers are said to be preparing to reopen it.

Canon City Coal Field, Colorado. 361

Diamond mine, — The Diamond mine is a small one-compartment inclined shaft 240 feet deep located on a nearly vertical coal bed onefourth mile east of the southwest comer of sec. 17, T. 19 S., R. 70 W., about 4 miles south of Canon City. It is owned by A. C. Dickerson, of Canon City, and operated under lease by Lewis, McCloud, Kingston and Gunn. The average production in November and December, 1908, is said to have been 75 tons a month.

The coal bed varies in thickness from 3 feet to 3 feet 6 inches. The following section was measured near the bottom of the shaft:

Section of coal bed in Diamond mine. Shale. Ft. Id.

Coal 1 2

Shale J

Coal 2 2

Coal bed 3

The coal dips about 75° E. in the upper 100 feet of the shaft, and about 55° E. in the lower 140 feet. It is probably the same bed as the one at the Nonac or No. 5 mine, but the absence of surface exposures between the two mines makes reliable correlation impossible. The operators report that there is about 2 feet of coal in an old prospect shaft about 75 feet west of the mine. It is possible that the coal in this prospect is a lower bed. In a crosscut driven eastward, across the strike, from the Diamond mine 2 feet 6 inches of coal was encountered at a distance of 90 feet. If the 75° dip observed at the shaft prevails across this distance the stratigraphic position of the three beds is approximately as follows;

Section at Diamond mine.

Ft. In.

Coal, in crosscut, reported 2 6

Rock 72

Coal, in Diamond mine 3 4

Rock 87

Coal, in prospect shaft, reported 2

166 10

The coal in this mine is hard but locally crushed. It shows in places a marked development of joints, which make lozenge-shaped patterns when viewed in horizontal cross section of the nearly vertical bed. The acute angles of these lozenges, measuring 20° to 35°, lie in the direction of the strike and the supplementary obtuse angles lie in the direction of the dip. Some of the joints are slickensided. They are evidently the product of the same compressive shear that upturned the strata of the western margin of the field. The superposition of the lozenge joints on other sets of joints running more nearly parallel to the directions of strike and of dip makes the joints

362 Contributions To Economic Geology, 1908, Pabt H.

very intricate where both sets are developed. This is in marked contrast to the simple joints in the mines located in nearly horizontal strata already described.

Royal Gorge mines,— The Royal Gorge Coal and Fireclay Company operates two inclined shafts on an upturned coal bed about 3 miles south of Canon City. The mines have a combined annual production of about 65,000 tons, most of which is shipped by rail from No. 2 mine. No. 1 mine, one-fourth mile north of No. 2, ships its coal by wagon for local use only.

In the Royal Gorge mines there are two coal beds about 7 feet apart which are mined together. A typical section in mine No. 2 is shown below :

Section of coal beds in Royal Gorge mine No. 2. Sandstone. Ft. In.

"Draw slate 2

Coal 4

Sandstone, fine, and hard shale 7

Coal 3 8

The upper bed is said to measure 5 feet 4 inches in mine No. 1, and the lower bed to measure 4 feet 6 inches in Alkali Gap, but these statements could not be verified owing to the inaccessibility of the old workings. A good coal bed 4 feet 6 inches thick, located about 165 feet stratigraphically above the Royal Gorge beds, was penetrated at a distance of 206 feet in a crosscut running 283 feet eastward across the strike from No. 2 mine. The following section was made in this crosscut:

Section of strata in crosscut CMst/rom Royal Gorge mine No. 2,

Ft. In.

Ro<'k, mostly sandstone 55

Coal, including a 4-inch clay parting 4 6

Sandstone 20

Shale 15

Coal 1 2

Shale, said to be fire clay 8

Sandstone, white, massive 120

"Draw slate, " above the Royal Gorge coal 2

225 8

Another section of the same coal bed, measured 100 feet south of the crosscut, is as follows:

Section of coal bed in level from crosscut east from Royal Gorge mine No. 2.

Sandstone. Ft. In.

Shale 1

Coal 2 6

Shale 3

Coal 1 2

Shale 2 5

Sandstone.

Coal bed v 3 11

Canon City Coal Field, Colorado. 363

About 200 feet west of the Royal Gorge bed Mr. Bettis has sunk a prospect shaft 95 feet deep in which a bed of coal 3 feet thick is said to have been struck at a depth of 75 feet. This is presumably the Nonac bed.

The method of working the two coal beds in the Royal (Jorge mines is interesting, because the beds are separated by only 5 to 7 feet of rock of moderate strength, of which more than half is firm shale and the remainder is sandstone in beds 5 to 12 inches thick.* The strata dip E. In spite of these apparently imfavorable conditions the coal is remarkably free from dirt, as reported in analyses made for the power plant of the Arkansas Valley Electric Company at Canon City, and as shown by about 9 per cent of ash in the analysis of a car sample of the pea and slack coal (No. 6248) .

The method of mining may be described as follows: From the main incline nearly horizontal levels are driven along the coals at about every 90 feet of depth. The coal is removed by upward stoping and drops through chutes into the mine cars on the levels. About 8 feet of coal is left temporarily as a roof to protect the levels. Black powder is used principally, with a small amount of giant powder in hard rock work. The lower coal bed is removed first and the thick parting of rock is allowed to settle into the stope, which it does slowly, breaking free from the bottom of the lipper coal, which is then mined by the same method. No rock needs to be hauled to the surface except that removed in driving the levels. In 1908 the fifth level was being driven, at a depth of about 450 feet. The relative percentages of products obtained are: Lump coal, 40 per cent; nut coal, 25 per cent; pea and slack, 35 per cent.

Hayes mine. — The abandoned Hayes mine, located about onefourth or one-half mile north of the Royal Gorge mines, probably worked the same coal bed. It was operated in the early days and the coal was hauled by wagon to Canon City. It is now completely caved in, and no information about it could be obtained.

Nonac mine. — The Nonac mine of the Colorado Fuel and Iron Company is located in Canon City, on the south side of Arkansas River. It is commonly known in the locality as No. 5, because it bore that number when operated by the Canon City Coal Company in the early days of this field. It is now No. 39 in the list of the Colorado Fuel and Iron Company. The mine is one of the oldest in the field, having been opened by Mr. Thornton in 1883.

The Nonac mine is worked from a slope running about half a mile to the southeast at an inclination of approximately 12°. The dip of the rocks at the mouth of the slope is 23° SE., but this high dip decreases within a short distance to 12°, which prevails throughout most of the mine.

364 Oontbibutions To Economic Geology, 1908, Pabt H.

The coal is the lowest workable bed in this locality, but it is about 70 feet above the Rockvale bed, which was cut through at the mouth of the slope but is worthless in this part of the field. The Nonac bed varies in thickness from 5 feet 8 inches to 6 feet 2 inches, except in the northern margin of the workings, where the coal is only 4 feet thick and contains a shale parting 10 to 12 inches thick near its middle. This parting wedges out toward the south and at a distance of one-fourth mile is represented by only a quarter of an inch of shale. Northeastward it thickens to 15 feet at the Prentiss shaft.

The mine employed about 90 men and produced about 300 tons a day before it was closed in December, 1907. The product was made up of lump coal, 55 per cent; nut coal, 20 per cent; pea and slack, 25 per cent. The mine is equipped with a steam 50-horsepower hoist, steam fan, wood tipple, stationary screens, and two electric mine pumps. At the time of the writer's visit in 1908 the mine was ventilated and kept in readiness to be reopened.

The coal from the Nonac mine is comparatively hard and stocks remarkably well. A large block of this coal several feet high has been standing exposed to the weather in front of a coal office in Canon City for sixteen years. (See p. 375.)

Prentiss shaft. — The Prentiss shaft was located near the center of sec. 4, T. 19 S., R. 70 W., about half a mile east of the Nonac mine. It has been abandoned for many years and no trace of it remains on the surface. John Arthur, of Canon City, reports that about 20 or 30 acres of coal was worked out from this shaft in 1888 and 1889, and that the coal bed was about 4 feet thick, becoming bony in the northern part of the mine. The mine had a good sandstone roof. The coal bed is 10 to 15 feet above the Nonac bed and is thought to be the upper bench of that bed, separated by the increased thickness of the parting which was noticed near the middle of the bed in the Nonac mine.

Littell mine. — Tlie Littell mine, in Wolf Park, 3 miles southeast of Canon City, is operated by the Colorado Central Coal and Mining Company, under the control of the Littell Brothers Coal Mining Company, of Colorado Springs. The shaft is located in the deepest part of the coal basin and has a depth of 1,065 feet, which is not exceeded by any other coal shaft in the State. The mine is on a bed of good clean coal 5 feet 6 inches to 5 feet 10 inches thick, probably the same bod which is mined at Chandler and which is exposed in an open cut in Alkali Gap, where considerable impurity is present. (See section, p. 358.) In 1908 mining operations were curtailed, awaiting the com[)letion of a spur from the railroad. The following section of the rocks was kindly furnished by the miners who sank the shaft :

CANON CITY COALr FIELD, COLOBADO. 365

Section of rocks in the shaft of the lAttell mine, Wolf Park.

Ft. in.

Sandstone, with blue pebbles 80

Conglomerate 10

Sandstone and conglomerate 110

Conglomerate, mostly 100

Sandstone and conglomerate in layers 250

(Total Arapahoe (?) conglomerate, 550 feet.)

Sandstone 100

Clay 40

Sandstone, solid 100

Sandstone, with clay partings 80

Coal 3

Sandstone, mostly 45

Coal 1 6

Sandstone (?) 12±

Shale 25

Sandstone 2 6

Shale 3 6

Coal, probably Brookside bed 2

Bone 3

Sandstone 22

Shale 2

Coal 10

Shale 5

Sandstone : 45

Sandstone, very hard, "quartzitic " 2

Sandstone and shale 7

Sandstone 6

Shale 9

Coal, probably Chandler bed 5 8

1, 065 6

The strike of the rocks at the bottom of this shaft is north and south; the dip 5° W. The shaft is equipped with a 75-horsepower steam hoist and an electric pump with a capacity of 100 gallons a minute. About 2,000 gallons of water an hour was entering the shaft in July, 1908, mainly from the upper sandstones and conglomerates. A little water also enters from the joints in the roof of the coal bed, but not in sufficient quantity to cause trouble. It is probable that when the water that enters the shaft from the upper sandstones is cased off there will be little trouble from this source.

At the time of the writer's first visit to this mine, in July, 1908, the shaft had reached a coal bed at a depth of 950 feet and prospect drifts had been extended on the bed for several hundred feet because it was thought to be the Rock vale bed, which is the lowest coal of this field. But on comparison of the foregoing section with the section measured in Alkali Gap (pp. 345-346), it became apparent that the prospect entries were being driven on a bed (the Brookside ?) that lies over 400 feet above the Rockvale bed and about 75 or 80 feet above

366 Contributions To Economic Geology, 1908, Pabt U.

the Chandler bed, which has an excellent development 2 miles north and 1 mile west of the mine. The Chandler bed was then sought by drilling and was encountered at a depth of 98 feet below the Brookside ( ?) bed. Those who now believe that the bed being worked at present in the Littell shaft is the Rockvale bed would do well to compare the section in the shaft with that in Alkali Gap. It will appear from this comparison that the Rockvale bed in the center of sec. 16 has a depth of about 1,450 feet, unless the rocks change considerably in thickness east of the gap. The Rockvale bed probably reaches a maximum depth of about 1,500 feet in the southwestern part of Wolf Park, which, therefore, must be either a deep syncline or a downfaulted block. A few east-west step faults, downthrown on the north side, have been encountered in the northern part of the Chandler mine. If more of these faults, or one large fault of the same kind, intervene between the Chandler workings and the Littell shaft, they may explain the discrepancy in depth of the Chandler bed in the two mines. In the imperfect exposures of Arapahoe ( ?) conglomerate that cover the intervening country no faults could be found. The dips fail by about 150 feet to explain the difference in depth. Dips determined in the conglomerate, which was laid down on stream beds that may have had an initial slope of 5° or more, are not satisfactory, and the true correlation of these beds must be ultimately determined by mining operations. Thus, on the east side of Wolf Park the bedding planes in the conglomerate dip 12° W. This conglomerate was laid down as coarse gravel by streams flowing eastward from the mountains. If the g:ravel beds had an initial slope of 5° E., like many of the de[)()sits in the existing creeks, the conglomerate must have been tilted westward through an angle of 12° plus 5°, or 17°. The coal becis would dip 17° W. under these conditions, thereby explaining most of the discrepancy in depth between the coals in the Littell mine and tliose east of Wolf Park. Failure to appreciate this structure and the fact that the overly barren measures are nearly 1,000 feet thick in Wolf Park has caused the abandonment of prospect drilling in this locality several hundred feet short of the most valuable coal bed.

No sample for analysis was collected from the main bed at the Littell mine, but a sample was obtained of the upper (Brookside ?) bed and tlie analysis (No. 6257) is given on page 373.

Brookside min. — The Brookside mine of the Colorado Fuel and Iron Company is located in sec. 11, T. 19 S., R. 70 W. It is one of the oldest and was once the largest producer in the Canon City coal field. Its product was well known and in high demand in Colorado. The mine was opened over twenty years ago and produced about 1,000 tons a day for several years, but the output was later allowed to fall to 250 tons a day, when the company developed other mines in which the cost of production was less. Since January 28, 1908, the mine

Canon City Coal Field, Colorado. 367

has been shut down, and at the time of the writer's visit in the succeeding summer the workings were rapidly filling with water. For this reason and for lack of ventilation it was impossible to enter the mine, hence all of the information obtainable was that derived from mine maps and from the miners left in charge of the property. The coal is the highest workable bed of the Canon City field. The operators report that throughout most of the mine the bed averages 5 feet 6 inches to 6 feet in thickness, but becomes thin and dirty at the south end of the mine, about a mile from the entrance. At the southwest end of the mine there is 3 feet of coal, and at the west end, east end, and center the sections are as follows:

Sections of coal bed in Brookside mine.

Central part of mine.

Sandstone. Ft. in.

Shale f-2

Coal 6

Bone 2

Goal 6

Coal.

Weit end of mine.

Ft.

in.

Bone.

Coal.

Coal bed

East end of mine.

Coal.

Ft.

In.

Bone.

Coal.

Coal bed

Coalbed 6 8

In mining the lower coal breaks from the bone, which is left as roof. The coal dips south-southwest, the angle of dip gradually decreasing down the slope. For the first 1,000 feet in from the entrance the dip is about 8 per cent, and for the next 4,000 feet it is about 6 per cent. The abandonment of the mine is thought to be permanent, as nearly all the coal that can be extracted profitably from this slope is said to have been removed.

Brewster mine. — The Brewster mine covered about 80 acres of coal of the Rockvale bed in the NW. i sec. 18, T. 19 S., R. 69 W. It has been idle for about ten years and the workings are completely caved in. No measurement of the coal bed could be obtained, but it is reported that the thickness varied from 3 feet 6 inches to 4 feet in the eastern part of the mine and was about 2 feet 6 inches in the northwestern part.

Magnet mine, — The Magnet mine of the Koeky Mountain Fuel Company, often called the Ocean Wave mine, is located near the center of sec. 19, T. 19 S., R. 69 W. In 1908 it was shipping about 200 tons a day. It is on a 3 to 4 foot coal bed, which is the first coal above the Rockvale bed on the east side of the field, the Nonac bed being absent except in the northwestern part of the field. At the end of the main slope in 1908 the coal was 4 feet thick, including two

368 Contributions To Economic Geology, 1908, Part H.

or three clay partings about one-eighth inch thick. In the sixth room off the third south entry the following section was obtained:

Section of coal bed in Magnet mine. Sandstone. Ft. In.

Shale 1 9

Coal 3 5

SUale.

In the main south entry 400 feet from the main slope the coal bed measured 4 feet inches, as shown below. The middle parting thickens northwestward in the mine, as shown by the section measured on the face of the third south entry from the main slope.

Sections of coal bed in Magnet mine.

Main month entry.

Ft.

in.

Third south entry.

Ft.

ta.

Coal

Coal

Shale

Shale

Coal

Coal

Coal bed

The parting is said to increase in thickness and in coarseness of grain to the northwest, becoming 2 J feet of sandstone at the northwest end of the mine. Three sets of joints were observed in the coal in this mine. The two strongest sets trend N. 60° W! and N. to 45° E. The former are 2 to 3 inches apart and the latter about 1 inch apart. A minor set of weak joints trending N. 30° W. was observed at a few places. The miners believe that the coal picks easiest on the east-west faces.

About the coal is machine mined. Three Sullivan electric chain-breast machines are used. For hand mining in 1908 the miners received 90 cents a fon. Considerable giant powder is iiecessary in many parts of the mine owing to the hardness of the coal, to the tightness with which it clings to the roof and floor, and to the local abundance of hard niggerheads." This is probably one of the causes for the low percentage of lump coal obtained. The relative proportions of the product are: Lump, 51 per cent; nut, 19 per cent; slack and pea, 30 per cent.

The mine is worked from a slope running westward down the dip of the bed. As in all the slopes starting from the eastern outcrop of the coal, the inclination is greater near the surface than it is farther down the slope. In the Magnet mine the dip is about 13° W. for the first 300 feet and then changes rapidly to 5° W. and finally to W. in the last 900 feet of the slope.

The room-and-pillar system had been followed up to the summer of 1908, when the long-wall system was adopted, because its use in the other mines of the field has fully demonstrated that it results in a saving of 15 to 40 per cent on mine timber and in a considerable

Canon City Coal Field, Colorado. 369

increase in the percentage of lump coal obtained, owing to the absence of crushing of pillars and to the greater ease of working a long uninterrupted face. In this mine there is locally also considerable "draw slate'' and other debris which is most easily disposed of by piling it immediately behind the miners as they advance the long-wall face. Owing to the bad shale roof, heavy timbering was formerly required in the mine.

This mine has little gas and most of that encountered is believed to come from the roof and the top coal. The fire boss reports having observed one small harmless blow of fire damp which came from the top of the coal and which was exhausted in a few hours. As in all the mines of this field, gas has never caused any trouble and safety lamps are rarely required and then only in places of local escape of gas.

The coal bed of the Magnet mine is not exposed at the surface but covered by soil. It is known to extend at least IJ miles south of the entrance to the mine. North of the mine the bed continues for about the same distance with varying thickness. In the wagon road southwest of the schoolhouse in sec. 12, T. 19 S., R. 70 W., the bed is reported by Simon Smith to be 5 feet thick. Near Mr. Smith's house, in the SW. J SW. i sec. 7, T. 19 S., R. 69 W., the coal is absent and the roof sandstone rests on the stratum beneath the coal. The same condition is reported in an old prospect about one-fourth mile northwest of the Emerald mine. It is probable that the absence of the coal is due to a ''sand roll" or local unconformity marking the position of a stream channel of the Laramie epoch.

Walsh mine, — The Walsh mine is a small mine from which coal was hauled by wagon. It is located about one-fourth mile north of the Magnet mine and on the same coal bed. The coal has about the same thickness as in the Magnet mine, but the parting in the bed is sandstone from 12 to 18 inches thick. The opening is said to be utilized at present mainly in drawing old pillars in the northern part of the Magnet mine.

Emerald mine, — The Emerald mine, owned and operated by Simon Smith, is a small mine about a mile north of the Walsh mine and 3 miles west of Florence, in sec. 18, T. 19 S., R. 69 W. The coal, which is probably the Rockvale bed, varies from 3 feet 3 inches to 3 feet 10 inches in thickness, including in places two clay partings each about one-eighth of an inch thick.

The mine is worked from a slope which in 1908 was 550 feet long. The slope is inclined 4° 45' for the first 300 feet from the entrance and 3° 40' for the next 250 feet. A similar increase in dip near the surface of the ground has been noted in nearly all the slopes on gently dipping rocks in this field. It is thought to be due in most places to the weathering and expansion of the underlying rocks. The coal is hauled from this mine by wagon.

7963**— Bull. 381—10 24

370 Contributions To Economic Geology, 1908, Pabt Ii.

WiUey mine. — The Willey mine is located in the SE. sec. 18, T. 19 S., R. 69 W. Entries Nos. 1 and 2, which opened on Oak Creek, are now abandoned. Entry No. 4, about one-fourth mile south of No. 2, is in a small gully that trenches the east side of the lower escarpment. None of these mines was large, and all of the coal was hauled from them by wagon, principally for local consumption. No. 3 is now operated by the Florence Fuel Company. It works the Rockvale bed, which has the following thickness:

Section of Rockvale coal bed in Willey mine No. S.

Sandstone. Ft. in.

' Draw slate " 2-18

Coal 3 6

Sandstone.

Santa Fe No, 8 mine, — No. 8 mine of the Atchison, Topeka and Santa Fe Railway Company is located on the steeply dipping western margin of the coal field, about 3 miles west of Rockvale. The mine was a steep incline, with a slope of about 30° E., about 1,000 feet deep, that worked a coal bed at approximately the same horizon as the beds in the Chandler and Littell mines. It has been abandoned for many years and can not be entered. The coal is said to be 4 feet 6 inches to 5 feet thick.

Bdssick mine. — The Bassick mine is a steep incline located on the upturned coal strata in the southeast comer of sec. 27, T. 19 S., R. 70 W. It is an old mine, having been opened over thirty years ago. The production was small and all the coal was hauled by wagon, most of it to the Bassick gold mine, on the west side of Wet Mountain. The mine has been idle for many years except during the miners' strike four or five years ago, when a few tons were taken out. The coal bed, which is said to average about 5 feet in thickness and to vary greatly in character, occurs at about the same horizon as the Royal Gorge beds or possibly about 50 feet lower. In 1908 the mine was filled with water and could not be entered beyond a distance of about 50 feet down the slope. At the latter point the following section was measured :

Section of coal bed n? the entrance to the Bassick mine. Shale. Ft. In.

Coal 1

Shale 2

Coal 4

(al bed 5 2

About 150 yards northwest of the Bassick mine the following section was measured on the east side of Oak Creek.

CANON CITY COALr FIELD, COLORADO. 371

Section northwest of Bassidt mine.

Ft. In.

Sandstone, resistant 20

Shale, sandy in the upper part 10

Coal, probably Nonac bed, surface measurement 2 1

Shale, carbonaceous, with sandy layers 20

Sandstone, soft, argillaceous, weathering white 20

Coal 4

Shale, carbonaceous, probably Kockvale coal horizon 2

Sandstone, soft, white, argillaceous, weathering into a sandy clay. 35

Sandstone, hard, yellow, thin-bedded, Trinidad sandstone 40

Sandstone and shale in beds 1 to 4 feet thick with ripple marks

and fossil leaves 25

Shale, Pierre.

174 5

Simon Smith shaft. — The Simon Smith prospect shaft was sunk for the purpose of reaching the Rockvale coal bed in the southern part of sec. 36, T. 19 S., R. 70 W. It is said to be 218 feet deep, mainly in sandstone, and to cut one workable coal bed. Work had stopped at the shaft in 1908, because the depth to the Rockvale coal bed was calculated to be 570 feet. Inspection of the strata at this locality makes it seem probable that the depth to the Rockvale coal is less than this, possibly not over 500 feet.

Coal prospect in the Dakota sandstone. — Verne Baumgartel has sunk a small prospect shaft on a coal blossom in the Dakota sandstone on his farm 3i miles south of Canon City. The bed is from 6 inches to 2 feet thick and stands nearly vertical, between beds of massive sandstone, from which it is separated in places by shale partings that are reported to be fire clay. The coaly substance is hard, black, and crushed by shearing movements along the bedding planes into lenticular, slickensided fragments 1 to 3 inches long. Although these shiny fragments closely resemble hard coal, it is evident from the high ash shown by the following analysis that the material is bituminous shale and probably of no value.

Proximate analysis of air-dried coal from Baumgartel prospect, miles south of Canon

CUy.

[Laboratory No. 6256.)

Moisture 8. 10

Volatile matter 24. 55

Fixed carbon 20. 91

Ash 46.44

Sulphur 48

Air-drying loss 8. 00

No other indications of coal have been observed in the Dakota sandstone in the Canon City region, although the formation is well exposed and it has been pretty thoroughly prospected for fire clay. A tunnel has been driven through the Dakota hogback at Canon City without encountering coal. Evidently there is no warrant for further efforts to find coal in the Dakota sandstone in tlda ,

372 Contributions To Economic Geology, 1908, Pabt H.

Character Of The Coal.

The coal of the Canon City field is well known in the West aa a high-grade domestic fuel. Practical tests have shown that it does not coke. When ground in an agate mortar, the powder falls clean from the sides of the mortar and does not adhere to the end of the pestle. This test has been found by M. A. Pishel,** of the United States Geological Survey, to indicate the noncoking character of a coal.

The absence of the coking property makes the coal cleaner to handle and therefore more desirable as a domestic fuel, although it would be better for steaming purposes if it had a tendency to coke. The coal is firm and hard and produces comparatively little dust in handling. It has a well-developed system of cubical joints, which are one-eighth to one-fourth inch apart, but the fresh coal does not break along these planes unless struck a hard blow. The coal bums with a short bluish flame under draft and with a slow whiter flame in a stove. Grates of the type commonly used under steam boilers are evidently poorly adapted to this coal, as an unusually dense and abundant smoke issues from the funnels when it is burned under boilers, as may be seen at the works of the United Oil Company in Florence and to a less extent at the Arkansas Valley Electric Company's power plant in Canon City. At the latter plant it is found desirable to mix the slack of noncoking Canon City coal with slack of coking coal from the Trinidad field. By careful regulation of the hand stoking and of the draft the smoke can be considerably reduced, but it is reported that a satisfactory grate has not been found for Canon Citv slack coal.

ft '

The chemical and calorific power of some of the Canon City coals will be found by inspection of the following table. Samples were collected from all the mines and sealed in galvanized-iron cans with adhesive ta{)e, but in the WTiter's ignorance of the rapid deterioration of coal under such conditions he kept many of these samples for several months after collecting. It is doubtful whether under such conditions an analysis of them would give accurate results or not. It will, therefore, be found that several of the principal mines are not included in the following table. The samples were all collected by cutting a uniform trench across the coal bed, then comminuting the material, mixing, quartering, and rejecting opposite quarters, the last process being repeated until the residue would fill a 3-pound sample can. Partings over half an inch tliick were rejected. The cans were sealed within the mines immediately aftr the samples were collected.

a Econ. Geology, vol. 3. ims. j). 2t;r..

Sec Tarr, S. W., ami Hamilton, J\. 1)., The weutherini of roads: Econ. (ieology, vol. 2, 1907, p. G93.

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Canon City Coal Field, Colohado. 3*75

The coal of the Canon City field stocks unusually well. . It may be kept for several years without much slacking, but of course, as in all coals, some deterioration sets in as soon as the coal is exposed. This is said to be less noticeable in the Canon City coal than in most western coals. The coal is not liable to spontaneous combustion, as attested by the large unbumed slack piles at several places. In the mine dumps it catches fire and bums slowly for years. Parts of old dumps which have been abandoned for several years are still warm from the slow combustion of the coal.

A good example of the keeping quality of the Canon City coal is a large block of the coal which stands in front of Mr. Rockefellow's retail coal oflSce in Canon City. This block, which was obtained from the Santa Fe mine No. 5, now the Nonac mine, had, according to report, been standing as an advertisement beside the street curb for sixteen years, protected from the weather only by a sheet of tin laid on its upper surface. The block was originally 5 feet high, this dimension being the thickness of the coal bed from which it was obtained, and 4 feet square on the base ahd top. When the writer examined the block in 1908 its height was still 5 feet, but it had lost from 6 to 8 inches from each side by spalling. Cubical checking was developed all over the surface of the block and two large cracks had cut nearly through it, necessitating a narrow band of iron around the block to prevent it from falling apart. The surface of the coal was somewhat dulled by the weather, but it was still black, without any whitening from the appearance of ash or the deposition of sulphur compounds.

The statements about the keeping quality of the Canon City coal apply with minor variations to the coal beds in the greater part of the field, from the lowest or Rockvale bed to the highest or Brookside bed. They do not apply so well to the coal of the southern part of the field, which is inferior in keeping quality. A large pile of coal at the Radiant mine, which had been exposed to the air for about four months in 1908, was slacking badly and deep checks had developed in the lump coal. About the lumps of coal there was much fine d6bris which had fallen from their surfaces. The miners stated that lump coal amounting to half of the lump coal originally m the pile could be obtained from it after this exposure to the weather. The Radiant coal bed is in the lower part of the Laramie formation, at an estimated distance of 200 to 250 feet above the Rockvale bed at the base of the formation. The cause of this slight inferiority of the coal from the south end of the field is not known. The coal is apparently not quite so hard as that from the north end of the field, but in jointing it is not noticeably different from the latter. The blocks cut down in mining at the south end of the field are considerably smaller than similar blocks in the northern mines. The coal

376 Contbibutions To Economic Geology, 1908, Pabt H.

seems to break much more easily along the bedding planes and also along the joint planes, but other factors may also enter into the problem. The writer does not intend to state that the coal of the southern part of the field is not a high-grade domestic fuel, but that it is not quite so good in keeping or weathering quality as most of the coal of this field.

There is considerable difference in the size of blocks cut down in mining in the different mines, owing partly to variance in mining methods and partly to inequality in the strength of the joints. Along the steep-dipping western limb of the syncline, from the Royal Gorge mine southward, intricate sets of closely spaced cross joints, meeting at acute angles, have been developed from the greater strain which the rocks have there undergone. In a few places the coal on the west side of the field is slickensided and crushed, but as a rule the joints show no evidence of slipping. Along this belt of nearly vertical and overturned beds large blocks of coal can not be obtained. The method of overhead stoping, required to work the steep beds, also lowers the percentage of lump coal obtained and increases the slack. Throughout the greater part of the field, however, the beds are nearly flat, dipping at angles of 2° to 5°, and laie blocks are cut down in mining. In the Chandler mine the writer observed a block of coal which had just been undercut and shot down that had the following dimensions: Height, 4 feet 1 inch, being the full thickness of the bed at that place; width, 3 feet; length, 18 feet. This block was too large for handling, but by using wedges it was broken into smaller blocks. It well exemplifies the strength of the coal. Similar blocks of smaller size are the rule in most of the mines. Shooting is always necessary, as it is difficult even to cut a small channel across the coal in obtaining samples. As a result of the strength and hardness of tlie coal and of the difficulties with which it is broken along the wide-spaced rectangular joints, the percentage of lump coal obtained in most of the mines is large. In the northern part of the field the range in sizes of coal from gently dipping beds is as follows: Lump coal, 45 to 70 per cent; nut coal, 15 to 30 per cent; slack and pea, 15 to 40 per cent. In most of the mines a much better showing could be made if greater care were exercised in mining, but the introduction of large numbers of careless foreign workmen who are paid by the ton of run-of-mine coal makes it difficult to increase the percentage of lump coal. In the early days, when the miners were all Americans, the percentage of lump coal is said to have been greater.

The sulphur content of the coal is low, as shown in the table of analyses. In unweathered coal the sulphur forms iron sulphides that make thin yellow leaf -like plates and spots on the joints and, rarely, in the bedding planes. Pyritiferous concretions are almost unknown in this field. Within 50 feet of the surface the coal is veined with

CANON CITT COAIr FIELD, COLORADO. 377

white stringers of gypsum and of iron sulphates derived from tlie weathering of the coal and the interaction of the sulphate solutions with calcium in the ground water.

Another feature of the weathering of the coal beds is their marked thinning out near the surface. Many coal beds that appear nearly fresh to the eye, except that the coal does not have its true luster, are reduced over 20 per cent in thickness by weathering. This is shown at a score or more of prospects, in which the coal does not have its full thickness within 10 to 25 feet of the surface. In the open cut on the Chandler bed in Alkali Gap a bed of coal which measured 6 feet, including partings, at a depth of 18 feet wedged out gradually to an 18-inch bed of coaly smut at the surface. At a depth of 6 feet, where to the eye the coal appeared but slightly weathered, its thickness was only 2 feet 6 inches. Prospecting in this field is not satisfactory unless carried to a depth of 15 feet or more, and surface measurements of coal beds on the outcrop are unreliable.

Economic Conditions.

The larger mines are reached by spurs of the Denver and Rio Grande and the Atchison, Topeka and Santa Fe railroads. The principal markets for the coal are in California, Kansas, Nebraska, Oklahoma, and Texas. Denver and other Colorado cities consume a minor part of the production. In July, 1908, the lump coal of one mine in the northern part of the field was being sold for $3.25 a ton f. o. b., and equally good lump coal of another mine was sold for $2.75 a ton f . o. b. The slack and pea coal are sold together at 50 to 90 cents a ton at the mines, depending on the amount of ash and on local freight rates. Most of this fine coal is used in factories and power plants in the adjacent territory.

The laborers employed in the mines are largely foreigners, among whom Italians are the most numerous. For piecework the miners receive the usual prices paid in this section of the Rocky Mountains, 45 to 85 cents a ton, depending on the difficulty of mining, the use of machines, etc. The workmen are not well organized, and there has been only one strike, about six years ago, when labor troubles caused many of the mines to close. As already stated, the mine managers report that the introduction of large numbers of foreign workmen has diminished the percentage of lump coal in the product, and in one mine it is proposed to pay the miners a premium based on the percentage of lump coal they produce.

The coal land in this field has all passed from the control of the Government to private and corporate ownership. In recent realty transfers the prices have ranged from $40 to $200 an acre, the higher price having been paid for excellent land tributary to a developed mine.

378 Contributions To Economic Geology, 1908, Paet H.

Summary.

The Canon City coal field is a small syncline of the Laramie formation, located in south-central Colorado, at the foot of Wet Mountain, which is the eastern range of the Rocky Mountain system in this region. The eastern limb of this syncUne dips westward at angles of to 5°, except at the northern margin, where the dips are 6° to S. This limb is broad in comparison with the western limb, being 2 to 4 miles wide and about 12 miles long. It contains all the larger mines of the field, eight in number, that ship by rail. The western limb of the syncline is a narrow belt of nearly vertical or overturned strata, not more than 1,000 feet wide. The mines on this limb are small, only two of them having railroad connections, but the Nonac mine, located at the northwest comer of the field, in the axis of the syncline, formerly produced about 300 tons a day.

The coal is a high-grade domestic fuel. It is bituminous, noncoking, and comparatively clean to handle. Its calorific value ranges from 1 1,000 to 12,000 British thermal units, the lower values characterizing the coal of the southern part of the field; all of that of the northern part exceeds 11,600 British thermal units. The keeping quality of the coal is excellent.

The Trinidad Coal Field, Colorado.

By G. B. Richardson.

Introduction. Location.

The Trinidad field is part of a large coal-bearing area, known as the Raton Mountain or, preferably, the Raton Mesa coal region, that lies along the eastern base of the Front Range in Colorado and New Mexico. The state boundary line divides this area into two approximately equal parts, the New Mexico portion being known as the Raton field and the Colorado portion as the Trinidad field. Although topographically, geologically, and economically the region as a whole is a unit, for descriptive and statistical purposes the twofold division based on political boundaries is convenient and has long been in use. The Raton Mesa region is one of several disconnected coal-bearing areas along the eastern front of the Rocky Mountains in Colorado, including the Denver, Colorado Springs, and Canon City fields. The coal in all these fields occurs in the 'Laramie" formation, which formerly occupied a much greater region than at present; probably all the fields were once continuous, but as a result of structural disturbance and erosion they have been separated into the present detached areas.

Previous Work.

The first systematic study of the geology of the Trinidad coal field was made by F. M. Endlich,** of the Hayden Survey, in 1875.

John J. Stevenson, in connection with the work of the Wheeler Survey, reexamined a portion of the area in 1878-79.

Ten years later Arthur Lakes published an account of this region in a report of the Colorado School of Mines.

In 1893 R. C. Hills included an account of the Trinidad field in his paper on the coal fields of Colorado, and this was followed

a Ninth Ann. Rept. U. 8. Geol. and Oeog. Survey Terr., 1877, pp. 192-206. b Rept. U. 8. Geog. Surveys W. 100th Mer., vol. 3, Supplement, 1881, pp. 102-225. . Trinidad or Raton coal fields: Ann. Rept. Colorado School of Mines, 1889, pp. 87-112. d Mineral Resources U. 8. for 1892, U. 8. Oeol. Survey, 1893, pp. 324-331.

380 Contributions To Economic Geology, 1908, Pabt H.

by the admirable series of reports, the El Moro, Walsenburg, and Spanish Peaks folios of the Geologic Atlas of the United States, bv the same author.

In 1902 L. S. Storrs " briefly reviewed the results of Hills's work in the Trinidad field.

A number of shorter papers relating to the Trinidad field, chiefly technologic, are listed below:

Hose A, R. M. Coal washing, a description of the Colorado Fuel and Iron Company's washery at Sopris, Colo. Minea and Minerals, vol. 17, 1897, pp. 478, 479, 521-524.

The Primero mines. Mines and Minerals, vol. 24, 1904, pp. 521-526.

Tercio and Cuatro mines. Mines and Minerals, vol. 25, 1904, pp. 218-223.

Segundo coke plant. Mines and Minerals, vol. 25, 1905, pp. 4-10.

Lakes, Arthur. Coal fields of Colorado. Mines and Minerals, vol. 19, 1899, pp.

Aguilar coal and oil district. Mines and Minerals, vol. 23, 1903, pp. 196-198.

The Occidental and other coal mines of Huerfano County, Colo. Mines and

Minerals, vol. 25, 1905, pp. 473-474.

Coals of the southern Colorado or Walsenburg and Trinidad region. Mining

Report, vol. 51, 1905, pp. 234-255. Meade, Frank. Coal mines of Pictou, Colo. Mines and Minerals, vol. 21, 1900,

pp. 1-3. McLaughlin, J. E. Barella Mesa coal field. Mines and Minerals, vol. 24, 1904, p.

Whiteside, F. W. The Delagua mines. Mines and Minerals, vol. 29, 1909, pp.

Valuable data arc also contained in the biennial reports of the state

mine inspector.

Present Work.

Considering that the Trinidad field is so well known, another, which is not a final report, seem superfluous. There has been, however, an increasing demand for information concerning this field, in connection with the sale of public lands, and because in the previous work no attempt was made to locate the coal outcrops reference to land subdivisions there has been no satisfactory basis for the classification of the area. A reexamination of the field therefore became necessary, and a party consisting of J. H. Gardner, D. E. Winchester, O. J. Bowman, J. B. Mertie, and the writer spent three months of the season of 1908 in the field, the primary object being to collect (lata on which to base the classification and valuation of the public coal lands. The work consisted chiefly in locating the outcrop of the principal coal beds with reference to government corners, measuring the thickness of coal beds, and obtaining samples of coal for analysis. In addition fossils were collected, and such attention as was possible under the conditions of the work was devoted to the general geology of the region.

a The Rocky Moimtain coal fields: Twenty-second Ann. Rept. U. S. Geol. Survey, pt. 3,

Trinidad Coal, Field, Colorado. 381

The location of the coal outcrops shown on the map (PI. XX) was determined by plane-table stadia traverse, on a field scale of 2 inches to the mile, based on the few government corners which were found in the vicinity of the coal outcrops, and which are believed to beauthentic. These are shown on the map by small circles. In some areas official resurveys must be made before the correct location of the coal outcrop can be established: There has been much contention over the location of government corners in this field, especially contiguous to the coal outcrop, and the condition of the land surveys is notoriously poor. It appears that in parts of the area corners were never officially established, and it is well known that some original monuments have been removed and that some comers have been illegally set. The network of sections and townships shown on the map is constructed according to data of the General Land Office and indicates a regularity throughout the field which probably does not exist.

A final report on this field must be postponed until the area is adequately surveyed, until the perplexing question of the age and correlation of the coal-bearing rocks is determined (which in turn must await more complete general knowledge of late Cretaceous and early Eocene paleobotany), and until the interior of the basin has been exploited with the drill.

Acknowledgments.

The writer gratefully acknowledges the cordial cooperation in the prosecution of his work of the officials of practically all the mining companies in the Trinidad field. A considerable mass of information, consisting of mine maps, diamond-drill records, etc., was placed at his disposal for study, but for business considerations much of this information has been withheld from publication. Thanks are especially due to Messrs. R. C. Hills, of the Victor Fuel Company; E. H. Wietzel, of the Colorado Fuel and Iron Company; J. D. Skinner, of the Northern Coal and Coke Company; F. Guiterman, of the Carbon Coal and Coke Company; and E. E. Shumway, of the Rocky Mountain Fuel Company.

Relief And Drainage.

The Raton Mesa coal region occupies a hilly country east of the Rocky Mountains at the border of the Great Plains and Cordilleran provinces. In the Colorado portion of the region — the Trinidad coal field — the surface elevations of the greater part of the area range from about 6,000 feet along the eastern margin to more than 9,000 feet above sea level at the west end of the field. Near the western border the Spanish Peaks, two conical mountains composed of igneous rocks which rise abruptly above the surrounding area and culminate in an elevation of 13,623 feet, are the dominating feature of

382 Contributions To Economic Geology, 1908, Part U.

the topography. At the southeast end of the field the lava-capped Raton Mesa, consisting of a number of dissected table-lands, rises to an altitude of about 11,000 feet. Fishers Peak, an outlying remnant of the mesa, is the most conspicuous landmark in the immediate vicinity of Trinidad.