Economic Geology and the Bulletin of the Society of Economic Geologists January-February 1922: Vol 17 Iss 1

1922 · Historical

Economic Geology and the Bulletin of the Society of Economic Geologists January-February 1922: Volume 17 , Issue 1. Digitized from IA1518511-02 . Previous…

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Economic Geology

VoL. XVII. JANUARY-FEBRUARY, 1922. No. I

: PARAGENESIS OF THE MARTITE ORE BODIES AND MAGNETITES OF THE MESABI RANGE.

Joun W. GRUNER.

In a recent investigation of the magnetic oxides of the Mesabi range' some interesting features were discovered in the work with polished specimens. That magnetite is abundant in the iron-bearing formation of the east end of the Mesabi range has been known a long time.? In 1917 J. F. Wolff published a paper in which he mentioned the abundance of magnetic oxides in the drill cores of the rest of the Mesabi range.* Since then Grout and Broderick have published a report dealing with the magnetites of the East Mesabi range in detail and referring also to those of the western part of the iron range.* The detailed work on the latter was carried on by the present writer for the Minnesota State Geological Survey.

This paper deals with the relations of the iron oxides to one another, and to the gangue minerals to a minor extent. Some difficulty was experienced in the preparation of polished speci-

1 Report in preparation.

Leith. C, K., "The Mesabi Iron-bearing District of Minnesota," U. S. Geol. Survey Mon. 43, 1903.

Van Hise, C. R., and Leith, C. K., "Geology of the Lake Superior Region," U. S. Geol. Survey Mon. 52, 1911.

8 Wolff, J. F., " Recent Geologic Developments on the Mesabi Iron Range, Minnesota," Proc. Lake Superior Mg. Inst., vol. 21, 1917, pp. 229-257.

Grout, F. F., and Broderick, T. M., " The Magnetite Deposits of the Eastern Mesabi Range, Minnesota," Bull. No. 17, Minn. Geol. Survey, 1919.

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2 John W. Gruner.

meiis, and in a few cases it was impossible to photograph features which were distinct to the eye only with the highest magnification (X 1600), but would not have shown clearly in any picture. About fifty specimens from various parts of the iron-bearing formation were examined.

Summary Of The Relations.

1. Magnetite is the principal iron oxide of the Biwabik ironbearing formation and is abundant throughout the range as far as Nashwauk. From this town westward the iron-bearing formation is much weathered, and magnetite occurs mainly in that portion that has been protected by the overlying Virginia Slate.

2. Magnetite is the oxide from which nearly all of the rich so-called "blue ore" has been derived, as can be seen by the abundance of hematite pseudomorphic after magnetite; in other words, the variety of hematite named martite. The stratigraphic relations of the unweathered formation to parts that have been leached of their silica and converted to ore support this conclusion.

3. Magnetite developed later than all the other minerals in the unweathered taconite,' with the possible exception of a little hematite which may be later than magnetite. (This relationship was also observed in a large number of thin sections. )

4. There are three generations of hematite, namely: (a) Hematite earlier than magnetite which will be called hematite of the first generation. (This does not refer to its relation to the gangue minerals.) (b) Hematite which is derived from magnetite. It will be referred to under the name of hematite of the second generation. (c) Hematite which is later than limonite in which it occurs as specular crystals. It will be called hematite of the third generation.

5. Magnetite may replace specular hematite and in turn may be altered to hematite again. —

6. Probably in almost all cases on the Mesabi range the alteration of magnetite to hematite is brought about by meteoric

The term taconite is used here to include every phase of the Biwabik formation with the exception of slates and paint rock.

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Paragenesis Of Martite Ore Bodies. 3

waters, as it occurs only in or near ore. This alteration has not been observed in absolutely unweathered taconite.

7. Limonite occurs most probably only as a late mineral where taconite is becoming weathered. It has not been found as pseudomorphs after magnetite or hematite. Much of it probably is derived from iron carbonate, greenalite, and ferromagnesian minerals.

8. Intermediate oxides and so-called solid solutions between hematite and magnetite,® if they exist, are rare and probably will defy detection for a long time to come. Extremely minute differences in the color of hematite and also in magnetite were seen with magnifications higher than 500 diameters, but they admit of no conclusions. They possibly are due to the grinding and polishing methods used.

g. Limonite occurs in practically every specimen which contains hematite of the second generation. This accounts for the "hydrated hematite" and "partly hydrated oxides" so frequently referred to in the literature of the Mesabi range.' There was found no evidence that anything but hematite and limonite occurs in the iron-bearing formation.

The Evidence For The Relations.

The writer in his field and laboratory study had an opportunity to examine the cores of more than a thousand drill holes in every part of the range. Wherever the taconite is unweathered, magnetite usually can be detected with an ordinary horseshoe magnet. The amount of magnetite found varies from a mere trace to specimens that contain 50 and more per cent. To give an idea of the abundance of magnetite, Figs. 1 and 3 are added. Fig. 1 represents a deep drill hole from the central part of the range. This hole is possibly a trifle richer in magnetite than the average vertical section from such depth. The percentage of magnetite

6 Sosman. R. B., and Hostetter, J. C., "The Ferrous Iron Content and Magnetic Susceptibility of Some Artificial and Natural Oxides of Iron," Trans, Am, Inst; Min. Eng., vol. 58, 1918, 409-433.

7 Van Hise, C. R., "A Treatise on Metamorphism," U. S. Geol. Survey, Monograph, 1904, p. 843.

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John W. Gruner.

was determined by the pull of the pieces of core on a hand

magnet. amount present with such

Practically all magnetite is euhedral in outline.

(After some experience one comes close to the actual

a method. ) Where this

does not seem to be the case, as on one side of the magnetite

Depth

By

Lower Slaty $

Drift

Vir ia Slate

Lite Carbonate & Slate GreenaliteT & Slate

Greenal T- & Sly

Chy. &Sly.T 12-15

Cyl. 12-15 30 Ghy 10-15 gi.

ChyT. oxidized 4 Algal Stra gtuce 10-15 Ch 16

Bd &ChyT. 20

Bat &Cgl 25 Sly.T &BAT. 5-10

8a T. 20

Bd. & SlyT 20-25

Ba T &Slate

5/5 Intermediate Slete

Lower Cherty w a

Greenalite &SlyT.

BaT. 20-22

Ba.T. 18-20

723

Key:

Teconite Coy. Cherty

Red Basal T. ACgl S Pokegamea Quartrite

Sly. Slaty Bd. - Banded

Conglomerate Numbers show average percentage of magnetite in Gore.

Pic:

Drill record from central part of Mesabi range to show the occur-

rence of magnetite.

grains in Plate I a, it is usually due to faulty polishing and,

focusing.

On account of the great differences in hardness of the oxides, carbonates, and silicates, it is difficult, if not impos-

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Paragenesis Of Martite Ore Bodies. 5

sible, to obtain specimens that do not show considerable relief after polishing.

The specimen in Plate I a illustrates euhedral magnetite grains arranged concentrically in the form of greenalite granules. No other oxide is present. The gangue consists of quartz (chert), carbonate and amphiboles, which represent a typical association of minerals, as the specimen itself is typical of taconite. Plate I c shows magnetite with a similar gangue in one of the characteristic dense bands of the lower cherty horizons of the Biwabik formation. The magnetite is also euhedral, and no other iron oxide is present. This is especially interesting, as the specimen comes from the rock wall of one of the large open pits of the central part of the range. Such a rapid change from magnetite to the oxides of the ore is found occasionally, but is not the rule. For some other reasons this specimen is noteworthy. It shows that the size of the magnetite grains is not in excess of one twenty-fifth of a millimeter. This material would form a considerable part of the recoverable product in case magnetic concentration should become one of the methods of extracting iron on the Mesabi range.

The specimen in Plate I 6 comes from a place within a few feet of that in Plate I c. The magnetite occurs in patches that are denser and commonly not in the shape of greenalite grains, while hematite in minute needle-like grains forms aggregates that have the outlines of greenalite granules in many specimens. The age of this hematite can not be fixed with certainty, though it appears as if the hematite grains were cut by magnetite in some places. Hematite replacing the magnetite along very minute lines, which can be seen only with very high magnification (X 1600) and are probably not wider than one two-thousandth of a millimeter, forms irregular patterns. They can not be assigned to any crystallographic directions of the magnetite. The same type of alteration along irregular extremely fine lines was noticed also in other specimens.

Surprising as it may seem, it has not been mentioned before that a large proportion of the ore occurs as martite. The so-

5 f 3 Z

6 John W, Gruner.

called high-grade "blue ore," as a rule, is soft and crumbles in one's hand. Almost any specimen of it shows, when viewed with a strong magnifying glass or microscope, innumerable glistening triangular faces that can be recognized as the well-known magnetite octahedron form. Plate I e shows such pseudomorphs and also residual magnetite. The alteration has gone to completion in the small crystals. It is noteworthy that the areas of magnetite are fairly massive and irregular, and hematite penetrates for only very short distances, if any, along crystallographic directions. This is still more conspicuous when compared with Plate I f. In this specimen, which is from a pit in the central part of the range, alteration along definite lines as well as along the edges of the magnetite shows clearly. Therefore, two kinds of replacement exist, one that begins along extremely fine lines which agree with no crystallographic directions, another that does. In the more advanced stages they can not be distinguished. The explanation for such an apparent difference in the behavior of replacement is that the change to hematite proceeds at first along lines that show either structural weakness like cracks or crystallographic peculiarities like parting, leaving the more massive portions to be altered slowly along the margins.

An apparent preference for one particular crystallographic direction may be noticed in Plate IIc. Such selective alteration is common and gives rise to hematite in the shape of rods, as in this plate, where one sees the hematite penetrating the magnetite crystals in parallel lath-shaped areas. Hematite with the same outlines, but without any magnetite, is also abundant, as can be seen in the same plate. As a matter of fact, most hematite that does not occur in the form of pseudomorphs has these shapes, as may be observed in Plates I b and d. To the writer it appears that this is a strong tendency of the hematite to form the specular crystals, even in the very fine felt-like aggregates, or also in some cases in the process of alteration from magnetite.

That hematite may be distinctly older than magnetite can be seen in Plates I d and II a, though the writer does not agree entirely with Wolff, who states that " the great mass of iron was

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Paragenesis Of Martite Ore Bodies. 7

laid down as original oxide (hematite and magnetite or an intermediate oxide), cemented together in an amorphous silica matrix."* In Plate I d distinct crystals of, magnetite are seen replacing patches of hematite needles of the first generation. Fig. 2

Fic. 2. Jasper granules probably replacing chert and hematite (hematite like needle-like aggregates in Plate I f). Magnetite replacing chert, hematite and jasper. Approx. X 200. illustrates a still clearer case of replacement. Here crystals of magnetite replace grains of jasper and at the same time hematite patches like those in the photographs. The jasper is perfectly clear and looks like quartz except for the reddish color when seen under very high magnification in reflected light.

There is little doubt in the opinion of the writer that the jasper grains are altered from granules of greenalite or some similar substance. Further, it seems reasonable that, if the hematite needles surrounding the jasper were younger than the jasper and magnetite, they would have penetrated or cut the jasper at least in a few places. This relation is actually found where hematite of the second generation occurs with quartz gangue in other specimens. At least, it seems the magnetite crystals would have been attacked, though slightly, by any development of hematite of the second generation, but they are unaltered, as shown in Plate I d

8 Wolff, J. F., op. cit., p. 234.

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8 John W, Gruner.

and Fig. 2. These two illustrations represent different specimens which come from the same stratigraphic horizon of the ironbearing formation. It is just above the basal conglomerate and varies from a few inches to 30 feet in thickness. For a better understanding of the position of this horizon a cross-section from the central part of the range, at right angle to the strike of the Biwabik formation, is shown in Fig. 3. The four large sub-

Greenstone

Above Leake Superior Level

Seale

Fic. 3. Cross section through central part of Mesabi range showing subdivisions of the Biwabik formation and abundance of magnetite. Heavy black lines along drill holes average 27 to 33 per cent. magnetite.

divisions in the section are those used by Wolff.°. The horizon just mentioned is always red in color and consists of jaspery, slaty and banded phases of taconite. (See also Fig. 1.) For several reasons I believe that this hematite is not due to oxidation by meteoric waters following down the dip as is commonly claimed for the origin of the ore bodies. They are:

1. This hematite horizon is found almost throughout the whole range, whether ore bodies are above it or not.

2. With the same regularity it occurs far down the dip, hundreds of feet below the Virginia Slate, where iron oxides due to weathering are practically unknown.

3. It consists of dense phases of rock which contain considerable amounts of carbonate, a mineral ordinarily not associated with oxides, formed by weathering.

4. No pseudomorphs or any other kind of alteration of magnetite to hematite has been noticed in specimens from this horizon, unless they were in or close to ore: bodies.

9 Op. cit.

Slat

PLATE Economic GEoLocy. VOL. XVII.

a. Euhedral magnetite in form of greenalite granules. X 20.

b. Euhedral magnetite in dense patches (grayish white); aggregates of hematite (white) in needle-like particles resembling greenalite granules. 20;

c. Euhedral magnetite (white) in gangue of carbonate and quartz; typical of rich magnetite bands in Lower Cherty. 200.

d. Magnetite (gray) replacing hematite (white needle-like aggregates) and gangue (black). 510.

e. Pseudomorphic hematite (white) replacing magnetite (gray). II0.

f. Hematite (white) replacing magnetite (gray) along octahedral planes.

Se a b — e f :

Il. 'Economic GEOLOGY. VoL. XVII.

a. Magnetite with outlines of specular hematite being replaced by hematite (white). 115.

b. Same as a highly magnified to show outlines of specular crystals with octahedral magnetite forming rims partly replaced by hematite of second generation. X 485.

c. Hematite replacing magnetite (gray); rod-like appearance of secondary hematite in partly altered taconite. X 450.

d, Specular hematite replaced by magnetite (gray); the latter in turn by hematite (white). Space between crystals filled with limonite (dark gray) At "X" sharp contact of limonite and magnetite. 200,

e. Euhedral magnetite (light gray) being replaced by hematite (white) in matrix of limonite (darker gray). Needle-like limonite projecting into quartz (black).

f. Specular hematite (white) developing in limonite. Black areas are holes in surface. 110.

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Paragenesis Of Martite Ore Bodies. 9

It may be safely assumed that hematite of the first generation also occurs in other horizons of the iron-bearing formation, below as well as above the Intermediate Slate, though the writer does not know the age of all the hematite. A fine specimen shown in Plate II a, b and d illustrates the complex history of the iron oxides and may solve some of the questions of the origin of certain ores. This specimen was obtained from an ore body 'by drilling, near Ely Lake, east of Eveleth. It comes from the upper half of the formation (Upper Cherty in Fig. 3) and was within 90 feet of the surface. In Plate II a one may see the large number of specular hematite crystal outlines which are commonly filled with magnetite and surrounded by hematite rims. Examination of these crystals under high magnification (Plate II b) indicates that these rims are, in most places, resolved into zones of hematite, magnetite and hematite, respectively, from the center toward the exterior. This specimen also shows that the hematite at the very rim is pseudomorphic after magnetite, as is proved by the study of the angles of the "saw-teeth" outlines and the residual magnetite. The only plausible explanation for such a structure is that hematite in the shape of specularite was the first to form. Magnetite replaced the hematite, leaving the outlines of the crystals as a whole undisturbed,- but asserting its strong tendency to form euhedral outlines of its own along the edges.

At the time when this specimen came within the reach of meteoric waters, and concentration of the ore began, the magnetite was in turn partly changed back to hematite. A piece of core from the massive, unweathered formation shows areas of magnetite which have the outlines of specular hematite. Here the change to magnetite was the last stage in the chain of alterations. A similar specimen from the Spring Mine of the East Mesabi range,"' on the other hand, illustrates the almost complete replacement of magnetite after hematite of the first generation

10 Specimen from Dr. T. M. Broderick's collection. His paper, "Some of the Relations of Magnetite and Hematite" (Econ, GroL., vol. 14, 1919, p.

360). contains another interesting illustration of the formation of martite on the Mesabi range.

: :

10 John W. Gruner.

by hematite of the second generation. Minute residual magnetite areas may be seen in the hematite under very high magnification. The writer suggests that such complex changes probably are not confined to the Mesabi range. : At any rate, it may explain the occurrence of residual magnetite in specular hematite in other districts. It does show clearly, as does also other evidence presented in this paper, that hematite is the alteration product from magnetite due to meteoric waters at relatively shallow depth—a fact which has been doubted by some geologists."

It is commonly stated that magnetite oxidizes to and becomes hydrated to limonite.'" This may be true of other districts, but I find no evidence of it in the Mesabi ores. In support of this statement Plates II d and II ¢ are submitted. Many other specimens were examined, but in none was found any oxidation and hydration of magnetite to limonite.

In Plate II d the dark gray material between the pointed specularite crystal outlines is limonite, which is in distinct contact with magnetite at the point marked (X). Since the hematite of this specimen is supergene after magnetite, as explained in an earlier paragraph, it seems that magnetite would have altered to limonite, at least partly, if any such tendency existed. The limonite is distinctly later than the magnetite, but not necessarily later than the hematite of the second generation. The same may be said of other specimens examined. In one which comes from the Genoa pit hematite is pseudomorphic after magnetite, while limonite fills the interstices without affecting the pseudomorphs. The specimen shown in Plate II ¢ is not advanced as far as the one from the Genoa pit, and only portions of the magnetite have altered to hematite, while much of the former is in sharp euhedral contact with the limonite which forms the bulk of the specimen. The limonite has no definite outlines resembling pseudomorphs of any other iron oxides and, therefore, resembles all other

11 Graton, L. C., Discussion of paper by Lindgren and Ross, "The Iron Deposits of the Daiquiri District, Cuba," Trans. Am. Inst. Min. Eng., vol. 53,

1916, p. 61. 12 Lindgren, W., and Ross, C. P.. op. cit., p. 52.

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Paragenesis Of Martite Ore Bodies. Ii

limonite observed. It never suggests any direct derivation from magnetite or hematite.

The writer does not wish to convey the, idea that limonite is not derived from magnetite or hematite. As a matter of fact, in some of his recent experiments both these minerals were dissolved in very weak sulphuric acid and humus solutions and precipitated as hydroxides or sulphides by the addition of certain carbonates or sulphates, but in such instances, which, of course, are common in natural surroundings, it is clearly a matter based on (1) reduction to ferrous iron which is taken into solution, (2) transportation, though often only very short distances, and (3) precipitation as hydroxide by neutralization or the becoming basic of the solution. A large percentage of the limonite is undoubtedly derived from iron carbonate, which is abundant in many places, and iron amphiboles, which are also of common occurrence throughout the range, though they had been reported only as far west as Mountain Iron.**

Plate II ¢ also indicates the manner in which the limonite penetrates the quartz gangue in needle-like aggregates along the contact. Needles might suggest goethite instead of limonite. A number of goethite specimens, among them crystals of the mineral, were examined. It was found that they were slightly lighter in color with a more bluish tint than those which the writer calls limonite. It is realized, of course, that there exists a possibility of mistaking one iron hydroxide for another, but the writer believes that all the specimens he examined contain only one kind of hydroxide of iron. Whether the needles represent the replacement of amphiboles is doubtful, since their arrangement does not resemble that of the radiating needles of ferromagnesian minerals. It is more probable that the needles are characteristic of limonite when it forms in minute amounts such as are often observed in places where limonite seems to be in the first stages of replacement of some gangue mineral, especially quartz.

That hematite in minute crystals will develop in limonite is shown in Plate II f. This specimen was found in one of the

13 Leith, C. K., op. cit., p. 159.

:

12 John W. Gruner.

numerous concentric cavities in the south rock wall of the old Norman pit at Virginia. These cavities originally were filled with carbonate (either calcite, siderite, or a mixture of both). The carbonate was dissolved' and limonite deposited in a rather porous form in parts of the cavities. Due to the character of the specimen, the polish is poor and the outlines of the microscopic specular crystals are not always clear.

Of course, it has been known that limonite changes to hematite by simple cold dehydration.** If much of the original sediments of the Biwabik formation was laid down as limonite, such a process may have converted the latter partly to hematite, as is thought probable by Emmons for the Lake Superior deposits,"® but that this process (shown in Plate II f) has been very extensive after the weathering of taconite to ore is not thought likely by the writer. That the hematite is in the form of specularite is most interesting and significant because it has been stated that specularite is a product only of hot solutions or deep-seated conditions.*° (Ransome has described spherules of hematite '" with crystal facets" which may have a similar origin as those in Plate II

The shape of the crystals as well as the association and field relation of the specimen were carefully studied. The latter consists entirely of somewhat porous limonite with the exception of the few hematite crystals,-and as limonite is not found in perfectly unweathered taconite it is reasonable to infer that the hematite is derived from the limonite, both minerals having been relatively close to the surface and in the zone of meteoric waters since their formation.

Conclusion.

In the "Summary of the Relations" the facts as found were presented. From them we learn that the history of the iron

14 Harder, E. C., "Iron-depositing Bacteria and their Geologic Relations," U. S. Geol. Survey Prof. Paper 113, p. 71.

15 Emmons, W. H., " Principles of Economic Geology," 1918, p. 293.

16 Van Hise, C. R.. op. cit., p. 844.

17 Ransome, F, L., " Geology and Ore Deposits of Goldfield, Nevada," U. S. Geol. Survey Prof. Paper 66, p. 124.

"a

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Paragenesis Of Martite Ore Bodies. 13

oxides of the ore bodies is more complex than it appears at first. The distribution of magnetite, together with amphiboles, and indications of intrusives as far west as Virginia,'* point to deepseated conditions and even regional metamorphism at the time the magnetite originated. Graphite in considerable amounts associated with the magnetite, and siderite, indicate the former presence of reducing material which could convert the higher oxides of iron into magnetite. How much of the latter was derived from earlier iron oxides, and how much from other ironrich minerals, is impossible to say. That hematite actually existed before magnetite and was replaced by the latter has been proved.

As to why the red horizon just above the basal conglomerate should have retained most of its iron in the form of hematite, while the beds above it contain the iron generally as magnetite, unless ore concentration has been active, is difficult to understand. It is probable, though, that the change from the Pokegama quartzite to the iron-bearing formation was a little more gradual than was formerly assumed. Due to the slow development of favorable conditions for the growth of the iron-bearing rocks, the beds immediately above the quartzite might not have received as much reducing material in the form of organic matter iti the course of deposition as the beds higher up. As a matter of fact, no graphite was seen in the red beds. It may be argued that the original strata contained the iron largely in the ferrous state, as carbonate or silicates, for example, a view which is shared by the writer, but that would not preclude the occurrence of ferric iron along certain layers, especially early in the deposition of the taconite.

A later change of magnetite to hematite apparently was confined to regions of ore bodies. This includes any incipient concentrations of iron-oxides brought about by the same processes in the same oxidizing environment. Limonite contemporaneously or subsequently was formed by solution of iron-rich minerals, including magnetite and hematite, and deposition of the hydroxide

18 Report in preparation.

+ :

:

14 John W. Gruner.

in open spaces. It is interesting to note here that the carbonates, whether calcite, siderite, or others, in the process of ore concentration, were leached out and carried away before the magnetite was changed to hematite, as can be told by the still magnetic but somewhat porous taconite. Limonite filled a part of these pore spaces. By dehydration very minor portions of the limonite were changed to hematite in the ore bodies.

It is hoped that this study will be of some help to those interested in the economic problems of the Mesabi range. The fact that magnetite is the protore of the rich blue ore over most, if not all, of the range means that large magnetite bodies of low grade are not confined to the east end of the Mesabi range, but are present in other portions of it, though not as accessible on account of the glacial drift cover and oxidation of some of the magnetite in a very erratic manner.

The writer is indebted to Dr. W. H. Emmons and to Dr. F. F. Grout for suggestions and criticisms.

University Of Minnesota, Minneapolis, Minn.

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SOME STRUCTURAL FACTORS IN THE ACCUMULA- TION OF OIL IN SOUTHWESTERN OKLAHOMA.

J. V. Howe

Introduction.

With the exception of a single paper' by Dr. R. C. Moore, no attempt has been made to discuss in their proper relations the structural features and the problems of oil and gas accumulation in the region south of the Arbuckle and Wichita mountains and north of the Red River. In the previous paper only that part of the region in the vicinity of Healdton is considered, and little attention paid to the. active area farther west. It is this large and important region whose structural relations will be considered here.

Stratigraphy.

Except in the immediate vicinity of the Wichita and Arbuckle mountains, the rocks exposed at the surface are of Permian age, and present the characters common to the redbeds. The Wichita mountains are composed chiefly of pre-Cambrian igneous rocks, with a few relatively small areas of Cambrian and Ordovician sediments, which dip away from the igneous core at angles of 4° to 20°, on the eastern and northeastern sides. The Arbuckle mountains consist of closely folded Paleozoic sediments, with a much less amount of pre-Cambrian granite. Immediately north of the Arbuckles, in eastern Garvin county, and south of the mountains in the Ardmore basin of eastern Carter county, rocks of Pennsylvanian age are at the surface, but elsewhere they are buried beneath younger beds. Reference to the geologic map (Fig. 4) will make clear these surface relations.

The presence of undoubted Pennsylvanian rocks has been proved in all that area south of the Wichita-Arbuckle axis.

1 Moore, R. C., Bull. Am. Assoc. Pet. Geol., vol. 5. pp. 32-48, 1921.

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North of the axis, however, owing to the presence of fewer wells and greater thickness of redbeds, little is known regarding its distribution. Presumably it is present beneath the redbeds throughout most of the area.

The various Paleozoic formations at or beneath the surface -have been described fully in many earlier reports,' and as nothing new has been added along that line, the descriptions will not be repeated. A brief outline of the physical characters is given in the Columnar section (Table I.).

Historical Geology.

From the beginning of the Cambrian period until the close of the Ordovician period it is clear that there was no important orogenic movement in the Wichita-Arbuckle region, for the exposed beds show sedimentation to have been continuous during that time. No trace has been found west of the Arbuckles of any rocks of Devonian, Silurian, or Mississippian age, yet this negative evidence should not necessarily be construed as meaning that they never were present, nor that they are not present today. Further study may result in the discovery of all three of these systems.

There are records of numerous wells which have passed directly from Pennsylvanian beds into beds of Ordovician age, hence it may be considered certain that there is an unconformity at the base of the Pennsylvanian. If any folding took place at this time it must have been slight.

Early in the Pennsylvanian there began a folding movement which culminated, at the end of the period, in the formation of the Wichita-Arbuckle mountains, and their related folds, the Criner Hills and the Red River arch. This folding was localized to such an extent that in many places it took the form of faulting, generally in a direction nearly parallel to the axis. This movement was concluded either in the latter part of the Pennsylvanian or immediately after its close. There then ensued a long period during which the Pennsylvanian rocks were subjected to erosional

2 See especially U. S. G. S. Prof. Paper 31, 1904.

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Structural Factors In Accumulation Of Oil. 19

processes and during which time the pre-Pennsylvanian beds were exposed at many places along the up-folds. Long though this hiatus must have been, and extensive as were its results, the region seems not to have gone farthér than a mature stage of erosion. The drainage at the beginning of Permian time seems still to have been in structural adjustment, and steep slopes were the feature of the topography. These statements will be further

'amplified in the discussion of the redbeds.

The Permian was a period of deposition of red shales and sands, during which the Arbuckles were wholly buried, and the Wichitas certainly were almost, and may have been entirely covered by sediments. At the close of the period southwestern Oklahoma became a land area, its uplift at that time being accompanied by slight warping along those lines of weakness which had been developed in the earlier and more intense folding.

Again, during the Cretaceous, a part of southwestern Oklahoma, perhaps as far west as Waurika, was covered by a shallow sea, this epoch being the Trinity. No notable folding accompanied this submergence, and the slight warping which followed the Cretaceous seems to have been local in its effects.

There is no distinct evidence of post-Cretaceous folding in southwestern Oklahoma, outside of those areas now covered by Cretaceous rocks. Some of the gentle folding in the redbeds area may have occurred at that time, but of this there is no evidence.

Regional Structure.

Major Structural Features.

The dominant structural features of the region are the Wichita-

Arbuckle uplift and the Red River Arch. (See Fig. 7.) Inti-

mately related to these major features, and produced by the same forces, are the numerous subordinate folds which are found throughout the triangular region between the Wichitas, Arbuckles and Petrolia, Tex. It is the purpose of this brief paper to point out the important relationship that exists between these larger flexures and the accumulation of the hydrocarbons.

A

20 J. V. Howell,

As a starting point it may be stated that every major structural feature of the pre-Permian beds is reflected in the Permian, but in a much less degree. The names used here will therefore apply

equally to the similar structures in the Permian and earlier beds. These structural features will be discussed in order.

Reayen

Fenpsyivaman

Simpson

Fic. 5. Generalized cross sections showing structure of southwestern Oklahoma.

The Wichita Mountains —A major flexure of the pre-Permian beds, extending at least from Granite, in Greer County, to Lawton, in Comanche County, where its extension to the southeast forms the broad Duncan arch. Intense erosion has removed practically all the Paleozoic sediments which formerly extended across the mountains, exposing the granite core. It is only

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Structural Factors In Accumulation Of Oil. 21

around the eastern end of the range that enough Paleozoic rocks remain to prove that the mountains are anticlinal in character. Dips indicated by the remaining Ordovician limestones and data furnished by wells drilled along the flanks of the range show that

'the north limb of the anticlinal is many times steeper than the south limb. The zone on the north, within which drilling offers chances oi success, is therefore much narrower than on the south. The north limb also is notably faulted, which is not known to be true of the south limb. .

At the west end the Wichita anticlinal flattens out and becomes, apparently, a low, broad arch. Data are scanty, owing to the fact that the pre-Permian sediments do not outcrop, and hence definite assertions can not be made. These relations are made clear by the structure sections (Fig. 5).

The Arbuckle Mountains —While less simple structurally than the Wichitas, the Arbuckle mountains nevertheless are anticlinal in form. They exhibit much more intense folding than the Wichitas, and faulting is more prominent. Less highly elevated originally, and now less deeply eroded, the Arbuckles exhibit less of granite backbone than the neighboring range.

The Arbuckle anticlinal also is asymmetric, but in this instance the steep dips are to the south, while those on the north flank are relatively gentle. There are numerous local folds within the mountains, all of which are nearly parallel to the main axis.

The Red River Arch—Hager'* has pointed out the existence, in pre-Permian rocks, of an extensive uplift along the south side of and parallel to the Red River. The north flank of the arch also is the steeper, and the heavy, competent beds of which the fold is composed, and which are within reach of the drill along the axis, are not met with, even in deep holes, a few miles north.

Like the Wichita and Arbuckle mountains, the Red River arch has a core of old igneous rock. Red granite has been found at a depth of 4,200 feet at Petrolia: dioritic schist at 2,600 feet in a well in 74—7s—6w near Terrell, Oklahoma, drilled in 1920 by the Sims Petroleum Co. Nine miles north of St. Joe, Texas, a well

3 Hager, Lee, Oil and Gas Journal, October 17, 1919.

:

22 J. V. Howell,

encountered fresh granite at 3,100 feet, but after passing through a considerable thickness of this rock the drill again entered limestone. This suggests a sill, but as there is no evidence of contact metamorphism, it is more probable that the condition has been caused by local faulting.

The Duncan Arch.—The surface evidence of a continuation of anticlinal conditions between the Wichita and Arbuckle mountains is not marked. Drilling has, however, shown unmistakably that such is the case, and that a broad, irregular arch dipping steeply to the north near the Wichitas, and gently to the south throughout its length, joins the two major uplifts. This buried part of the Wichita-Arbuckle axis is termed the Duncan arch. The approximate location of its crest is shown in Fig. 7.

On the crest and flanks of the Duncan arch are located most of the important pools of southwestern Oklahoma, and from the standpoint of petroleum geology it is a feature of first importance.

The Criner Hills —Southwest of the Arbuckle mountains, and lying chiefly in T5S, RIE, is a small area of pre-Permian rocks forming the Criner hills. Beds of Pennsylvanian and older rocks are folded and faulted in a manner similar to that in the Arbuckles. The structure of the Criner hills is that of a crumpled and faulted anticline whose axis bears about northwestsoutheast. The lower Pennsylvanian beds dip away from the hills at relatively high angles.

The Cement Fold.—Owing to its position several miles north of the Wichita-Arbuckle axis, and its lack of definite relationship to the major uplifts, the Cement fold is sometimes considered as a major structural feature, bearing a relation to the mountains which is similar to that of the Red River arch. However, it seems better at this time to consider it merely a pronounced fold on the south flank of the Washita syncline. The Cement fold has been recently described by Reeves,* whose view of its structural relations is in substantial agreement with the foregoing statements.

4 Reeves, Frank, "Geology of the Cement Oil Field,' U. S. G. S. Bull. 726 B.

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Structural Factors In Accumulation Of Oil. 23

The Red River Syncline—Between the Wichita-Arbuckle axis and the axis of the Red River arch, but with its trough near the latter, is the Red River syncline. The broad, digitate head of this syncline lies in eastern Jefferson County, and it extends from there westward along the north side of the river, a deep, wellmarked feature, at least as far as Eldorado, where it becomes wider and flatter, and probably loses its identity in the prevailing southwestward dipping monocline. The synclinal fold is asymmetric, its south limb being much shorter and steeper than the north limb.

The Ardmore Basin.—Between the Arbuckle mountains and the Criner hills is a structural basin which seems to have persisted as such since the first uplift of the mountains took place. The work of many geologists' has shown that during the Pennsylvanian at least this basin was the site of deposition of an extraordinary thickness of sediments. Until late in the period the Ardmore basin probably was separated from other Pennsylvanian areas to the north and west, but it seems clear that a connection must have been established in upper Pennsylvanian time.

The Washita Syncline——North of the Wichita~-Arbuckle axis, and with its trough following, in general, the course of the Washita River, is a broad, deep syncline which is usually referred to as the Washita. This great depression seems to have had no direct contact with the Red River and Ardmore basins during most of the Pennsylvanian, and certainly was separated during ali but the latest Permian. Proof of this may be seen in the fact that no gypsum beds are found south of the Duncan arch, though - occurring but a short distance to the north. The thick Duncan sandstone occurs close along the north flank of the arch, but never appears to the south, although stratigraphically it might be expected. In general the Permian beds north of the arch carry more sand than those to the south. That part of the Pennsylvanian which immediately underlies the Permian in the Washita area includes almost no limestone, whereas that on the south side

5 Taff, J. H., U. S. Geol. Surv. Prof. Paper 31, p. 50, 1904; Moore, R. C., Jour. Am. Assoc. Pet. Geol. Bull. 5, pp. 37, 38, 1921.

; t

24 J. V. Howell.

of the arch contains limestone beds in considerable number and sometimes many feet in thickness. This last difference may, however, be due to an unconformity between the Permian and Pennsylvanian, the upper Pennsylvanian being absent south of the arch.

Relation Of Permian Beds To Major Structural Features.

Thickness——In 1917 Aurin published a map*® on which was shown by "lithobathye lines" the thickness of the redbeds in Oklahoma. Owing to lack of data this map did not show in much detail the conditions in southwestern Oklahoma, although it did bring out the fact that the-redbeds thicken away from the Wichita mountains. In 1921 Burton' discussed in greater detail the relation of thickness of redbeds and the producing areas in the Healdton area, and pointed out that along all of the producing folds the redbeds are thin.

The map (Fig, 6) shows, also by "lithobathyce lines," the thickness of the redbeds in both the Wichita and Arbuckle areas, as shown by the most recent drilling. The rule stated by Burton, that "the redbeds are relatively thin over the producing fields," is here shown to apply to a much wider area than that for which he originally stated it. Over every productive field in southwest Oklahoma the redbed cover will be found to be markedly thinner than in the zone immediately surrounding.

There seems to be no definite relation between actual thickness of the Permian and accumulation of hydrocarbons, yet there may be some significance in the fact that south of the Duncan arch no production has yet been secured where the redbeds are thicker than 1,500 feet. Where the redbeds are relatively thick tests have been uniformly dry, even though located on splendid domes. Such a case is the Roxana test in 12—3s—Sw, a well located near the top of a closed structure, yet finding salt water in all sands. The redbeds here are several hundred feet thicker than in nearby

6 Aurin, Fritz, " The Red Beds of Oklahoma," Okla. Geol. Surv. Bull. 30,

7 Burton, Chas. E., Bull. Am, Assn. Pet. Geol., vol. 5, pp. 173-177, 1921.

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Structural Factors In Accumulation Of Oil.

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wells. A similar condition is found in the non-productive south half of rs—ow, between the Walters and Empire fields.

There are several possible interpretations® of this condition, but the one which seems best to fit the facts is as follows: Following the Pennsylvanian the region was subjected to erosion for a period which did not reduce it to base-level, but developed a topography which was controlled by the structure of the Pennsylvanian rocks. The major divides were chiefly anticlinal; the major streams flowed in the synclines, while many of the minor streams also retained a structural adjustment. As the Permian sea advanced from the west, it naturally filled first the valleys (synclines) and gradually covered the hills (anticlines). Finally the entire post-Pennsylvanian topography was buried beneath many hundred feet of sediments; minor foldings (chiefly along those lines established at the close of the Pennsylvanian) again took place, and the land was again uplifted. Thus far the streams have not yet uncovered the old land surface and their present courses are controlled chiefly by the structure of the redbeds. Most of the major streams of the redbeds region are synclinal, though this is by no means the case with the tributaries. Thus the redbeds are thickest in the pre-Permian synclines and thinnest over the structurally high areas. Since most of the accumulation of oil and gas is in the Pennsylvanian rocks, the importance of this relation is obvious.

Attitude of Beds——The determination of " normal" or regional dip in southwestern Oklahoma has always been a matter of some difficulty, and particularly in the area south of Duncan there has been much difference of opinion as to the direction of dip. In general the regional dip of the Permian beds is away from the major anticlinal features. By referring to the structural map (Fig. 7) the direction at any particular place can be determined

Along a line extending from about the northeast corner of T1N-—RoVW in a southeasterly direction some 25 miles, and passing through the town of Duncan, it is difficult to determine any regional dip at all. This line follows the crest of the Duncan

8 Burton, C. E., op. cit., p. 175.

arch, and probably the beds here are nearly horizontal.

Structural Factors In Accumulation Of Oil. 27

North

of this axis the redbeds dip rapidly northward toward the

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[SS Gor Dizts S Fic. 7. Structural sketch map of southwestern Oklahoma showing location

of anticlinal and synclinal axes.

Washita syncline, while on the south they dip gently toward the Red River.

Secondary Structural Features.

Folds on Major Arches.—Oil and gas in the southern Oklahoma region have accumulated chiefly in smaller domes and anticlines on the crests or flanks of the major folds. ondary structures are for the most part arranged along definite lines, their axes being slightly oblique to the direction of the main There are several of these secondary axes along the south side of the Duncan arch, the most extensive of which is the Healditon fold, extending from the Healdton field northwest through the Comanche and Empire fields.

axis.

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28 . J. V. Howell.

in at least six places. Other well-defined lines of secondary folding can readily be noted in Fig. 7.

With but two important exceptions, all thoroughly tested domes and anticlines located on the major folds have proven productive. In one instance, north of Loco, in T2s—-R5w, a deep test on a small dome found no sands below the base of the redbeds, at which depth a small showing of gas was noted. No salt water was encountered. Tests on the large Nellie dome in Tin—Row have thus far failed to produce, but there is evidence that the sands in which oil occurs farther east have here been cut out by an unconformity.

Folds in Major Synclines.—There have been tested, to sufficient depth, some half dozen well-authenticated domes and anticlines which lie within the Red River syncline. In all of these salt water has been found in every sand and there have been only minute traces of oil or gas. This is what might well be expected.

Minor Synclines——Minor synclines, some of which are relatively shallow, are exceedingly effective in cutting off production. Such troughs intrude into the Walters, Empire, rN—ow, and other pools, and carry water only, or water and oil in such relation that one can not be obtained without the other. In a field like Healdton, where the sands attain a great thickness, the effect of local synclines is negligible, but in a majority of the southern Oklahoma fields the sands are comparatively thin and the synclines have an important effect on development.

The prevalence of water in the Thomas or 2,000-foot sand in the Parsons-Gant pool in 25—1m—9w may be explained by the extreme flatness of the beds at this point. In the Gypsy Oil Co. No. 1 Fowler, 25—1-ow, the Thomas sand is 41 feet in thickness, but this seems to be somewhat greater than is usual. However, when a sand of this thickness lies in a nearly horizontal position, and only slightly above a shallow syncline, as in this case, it is by no means surprising to find the lower part of the sand filled with water.

Relation of Structure to Accumulation.—In the fields of southwestern Oklahoma, with few exceptions, the anticlinal accumula-

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tion theory is found to hold. In the few apparent exceptions it is probable that more complete data will permit including them also. All known productive areas in the region are included in Table II. and a synopsis of their important characteristics is given. It will be noted that in only a few cases is there any doubt as to the effect of structure.

Relation of Structure to Proportion of Oil and Gas.—There are four areas in southwestern Oklahoma where gas is found in enormous amounts and seems to predominate over the oil which also is present. These areas are as follows:

east end. or Keys field TJ row 24, 25-Is-9w and 18, 19-1s-8w southern part of T 2s-R sw

There seems to be no definite relation between the regional structure and the predominance of gas. That is, the location of a pool high on the regional structure does not necessarily mean that it will produce gas chiefly. The large gas fields may as - often be found well down on the flanks of the major folds. However, in each of the gas areas mentioned the gas is found in the highest parts of the domes, and the important gas-producing domes are structurally higher than surrounding or related domes that produce oil. Thus the so-called Keys field is the highest part of the Walters fold; the Fort Ring pool is structurally higher than the Empire pool, to which it is closely related. A similar condition exists in the Fox pool, which is related structurally to the Two-Four and Graham pools, but, being higher than either of them, has acquired most of the gas. In the Loco pool the conditions are less definite, as the dome on which production occurs is somewhat isolated, in so far as present development has shown. Each of the important gas areas may best be considered as having been the recipient of the gas from structurally lower folds closely related to it.

Relation of Depth to Proportion of Gas and Oil.—The general thesis that gas occurs more commonly in the higher strata of a

:

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Structural Factors In Accumulation Of Oil. 33

region, and oil in the lower, holds commonly for the fields of southern Oklahoma. But, as is usually the case, there are many local exceptions. In general, any well which is a heavy gas producer in an upper sand can be expected to produce oil in the deeper reservoirs.

Summary.

1. The main structural features of southwestern Oklahoma include the Arbuckle and Wichita mountains, with their low connecting fold, the Duncan arch; the Criner hills; Red River arch; Cement fold; and the Red River, Washita and Ardmore synclines.

2. The Permian redbeds are relatively thick over synclinal areas and thin over those whose structure is anticlinal. While this condition is most pronounced in its relation to regional structure, it is found to hold true also with regard to the minor folds.

3. Anticlinal folds located on the flanks of the major up-folds have been productive in every case where sands were present. No single instance is known of a productive anticline lying in a regional syncline. Hence it would appear wholly unwise to recommend drilling in this region except on the major arches.

4. Every instance of commercial accumulation of oil and gas in the region (except perhaps that at Granite) is directly and definitely related to some anticlinal type of structure, although such fold may not be closed.

DEPARTMENT OF GEOLOGY, STATE UNIvERSITY oF Iowa, Iowa City, Iowa,

J

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PLAIN GEOLOGY. GerorGE Otis SMITH.

Some years ago I spoke to an audience of mining men on the subject of plain writing. My talk was an appeal for the simple and direct statement of scientific thought in popular language; but that appeal was addressed to consumers of geological literature, and I should probably do better to make a similar appeal to some of the producers of geological literature.

Geology has of late been presented to the public in so many new aspects—commercial, military, political, and even legal— that he would be bold who would add to: its modern varieties; therefore I ask here only a return to a primitive type, and my topic is "' Plain Geology."

I am convinced that, at its best, science is simple—that the simplest arrangement of facts that sets forth the truth best deserves the term scientific. So the geology I plead for is that which states facts in plain words—in language understood by the many rather than only by the few. Plain geology needs little defining, and I may state my case best by trying to set forth the reasons why we have strayed so far away from the simple type.

First of all, I suppose we may as well admit a certain liking for the sound of words, and the longer the word the more sound it has. Especially enjoyable is this mild form of hypnotism if both ideas and words are such as to make us feel that we are moving in the highest circles. At the meeting of the British Association this year one physicist frankly explained that the idea of relativity is popular because to most people it is " pleasantly incomprehensible." It was a hardened reader of manuscript who confessed that he liked to hear a psychologist talk. "' Of course, I understand not a word he is saying, but it is a noble and ai

1 Presented before the Society of Economic Geologists at the .\amherst Meeting, December 28, 1921.

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Plain Geology. 35

inspiring spectacle to see a mere human being crack a whip over an entire vocabulary and see the words jump up on their little red chairs like so many trained seals." But, as I wish to suggest, doing tricks with words may be more entertaining than really useful.

Again, I fear lest in our writing we lose sight of our audience, if, indeed, some of us ever see at all the audience to whom we address our written reports. The chief purpose of words is to convey thoughts, and unless the wave-lengths of the words are right the receiving apparatus will utterly fail to pick up the thoughts. How easily we can underestimate the difference in vocabulary between our audience and ourselves was brought to my notice recently when I heard a brother geologist speak at a

dinner to a large group of oil operators, highly intelligent but not

broadly educated men, to most of whom the oil business was simply a profitable side line. I thought the talk unusually free from the technical terms so commonly used in the inner circle of our fraternity and was therefore surprised when a table companion remarked that this talk didn't get across because it included many words not understood by the majority of those who heard it. I asked for particulars. and he at once specified "periphery," a word the speaker had repeatedly used in describing where to test out this or that oil pool. " Half of those people don't know what ' periphery' means," said this gentleman, who knew the audience better than I did, and I saw that he was right; and then I realized how much better that common every-day word "edge'' would have served—so many things have edges and to so few do we need to attribute peripheries! And when we come to think of it, we realize that "edge" is a sufficiently exact term to apply to an oil pool, the position, shape, and extent of which we know only in very general terms.

This brings me to a third reason for our use of highly technical language: we too often try to overdress our thoughts. Just as there is a somewhat prevalent notion that clothes make the man, so we subconsciously believe that words make the idea. We follow the precept, " To be scientific, use scientific terms," and in

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36 George Otis Smith.

so doing we deceive ourselves. I do not wish to be unduly autobiographic in this analysis, but to show my true sympathy for those whose practices I denounce, I confess that I, too, have had the unhappy experience of stripping the technical words from what looked like a good-sized geological deduction only to find that the naked idea was rather small and not my own. It is also a common experience to make the sad discovery that*a piece of involved and obscure writing is simply the product of roundabout reasoning or twisted thinking. Our own words fool us, and unconsciously we cover up with long words or tangled rhetoric our lack of plain thinking.

In picking my samples of the wordy sins of scientists, I naturally turn to the writings of my associates on the United States Geological Survey, not because they are the worst offenders but because they are sinners with whom I am best acquainted. Some of these writers, after setting down a technical phrase, realize the need of reaching their readers with words more easily understood and so translate their own scientific terminology on the spot; for example, one good geologist refers to "disseminated grains scattered through the rock," and another addresses the two parts of his audience with this sentence, " Disintegration is slow in these rocks, and they do not break up rapidly." " Disserhinated " and " disintegration' are words that please every ear, trained or untrained, while the garden variety of mind is helped along by the plain words "scattered" and "break up."

It seems that in our hunt for general principles we feel the need of tagging each observed fact with some word that may connect it with the language in which the great fundamental laws of the universe are proclaimed at the seats of learning. For this reason—lI prefer to suggest no other—a Survey author refers to cracks and crevices in rocks as "spaces of discontinuity." I remember a long sentence in the manuscript of a report on a western coal field in which the fairly common fact that shale is softer than sandstone was stated with full acknowledgments to " differential erosion" and due respect for the "physiographic cycle,'

terms very comforting to the graduate student at our greater

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Plain Geology. 37

universities, but not at all useful to the practical man trying to open up a coal mine in Montana.

It takes years for some geologists to break the fetters of this scholastic habit of using big words for small ideas. Probably every one of us has been guilty of sentences like the following, which appeared in a Survey manuscript: " The argillaceous character of the formation is very prominent in some localities, although it is usually subsidiary to the arenaceous phase." On being translated this means: At some places the formation includes considerable clay, but generally it is made up chiefly of sand.

In our writing I believe, however, we are tending to write more plainly—to say "sand" instead of "arenaceous deposit," "clay" instead of "argillaceous stratum," "close folding" instead of "intense plication," "river banks" instead of " riparian borders," "mouth" instead of " debouchure," "shore" instead of "littoral margin," and "the overlying bed is limestone" instead of "the superincumbent material consists of a stratum of calcareous composition."

I even hope the day.may come when more of us will say "beds" instead of "strata," for the context usually shows that we are talking about rocks, not about furniture. "I, too, love the sound of "strata," but all the pleasure I get from it is wholly lost when those who strive to copy our learning speak of "stratas."" As a measure of our progress, may quote from a Survey author of an earlier day, who referred to "autogenous hydrography on a vertically heterogeneous terrane *—truly a nut of a thought, which [ll not try to crack, lest I find it all shell: It was a Survey graduate, I believe, who defined '" form value" as "an intangible quality expressing the broad applicability of the energy form in contrast to its theoretical thermal value as commonly expressed in B. T. U." Words fail me, either to translate that definition or to describe it, though I may apply to such language a few words used in another connection by a Survey writer: "This holds the promise of large potential possibilities."

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38 George Otis Smith.

But I do not wish to claim for the Federal Survey any monopoly in learned writing. It was one outside of our fold who urged me to use plain language at a meeting where we were both on the program. I tried to follow his excellent advice, but in his own address before a mixed audience I listened with rapt attention to sentences like this: "So now every legitimate evidence of fact and deduction points to the origin of microbic unicellular life in the moist, subaérated soil away from the direct sun; and the soils of today are alive—a mighty host—with such microbic creations existing under paranerobic conditions." Before such words I realized that I, too, was a layman, for what I heard was, in the words of the speaker, " difficultly intelligible," if, indeed, I might not appropriately adapt to my use other sounding words in the same address and frankly confess that such language "outstripped the early promise of my cephalic ganglia and left me hopelessly decephalized."'

Technical terms have their places, and I am on record as admitting that exact scientific statement needs special terms, words that best keep their razor edge when used only for hairsplitting distinctions. This limited use of a highly specialized terminology is wholly defensible, for it would be folly to throw away tools so well fitted for special purposes, just as it is unwise 'oO put them to everyday uses with everyday people. " Transsubstantiation," "transpiration," and "transgression" are technical words that are useful enough to the professional theologian, biologist, and geologist, but they are code words that must be decoded before others can understand them. We know that a telegraphic code saves words for those who use it, but it also most effectively conceals information from the uninitiated.

I have a very definite purpose in this appeal for plain geology that a larger part of our people can understand. Today our science has more contacts with life than ever before: industry has taken geology into partnership, and engineers and capitalists and statesmen all look to geologists for advice. This greater demand has called to the ranks many with varying degrees of professional incompetence, a polite phrase by which I mean in plain English

:

ard

—

Plain Geology. 39

that some who call themselves geologists are knaves, others are fools, and yet others are hybrids. Now, the universal camouflage of the fake geologist—whether of the untaught or uncaught variety—is his protective coloring of technical words. To his clients or his dupes who are weak in geological knowledge these long and unusual words are impressive and serve his purpose, but to those who have had the advantage of special training and experience his use of geologic terms at once exposes his true character. Indeed, this is the basis of the practical test that some of us apply to the report in an oil prospectus if, as so commonly happens, we have never heard of the so-called " well-known authority on the geology of the greatest oil fields of the world." Such an expert uses all the latest terms, but he mixes their meanings, his report is senseless, and we know him to bea faker. But I have yet to note the fake geologist imitating plain statements of geologic facts—that kind of masterpiece he doesn't attempt to copy. So I suggest this method of protecting our useful science from successful imitation: the economic geologist should tell his story in plain English, then because of the transparency of his statements his clients or the public can see things as they are and will learn to refuse the highly colored substitute offered by his quack imitators. i

There is really somewhat of an obligation upon us, both as scientists and as partners in the world's business, to show the world that geology is not mystery or magic, but only common sense. I have told practical men of business that they should give little credence to the geologist who. can not tell his story in common language. The world has a right to discount our usefulness and even to distrust our honesty if we persist in concealing our thoughts, or lack of thoughts, behind a mask of professional jargon. The lawyers and the physicians whom I trust most can and do explain their technicalities to me in words that

I can understand. Isn't plain geology the safest and most useful kind ?

Director, U. S. GroLocicaL Survey, WasHIncrTon, D: C.

Editorial

On The Estimating Of Petroleum Reserves.

Eminent and able geologists of national reputation have issued warnings of the imminence of the exhaustion of our petroleum resources since the earliest days of the development of our production of that extremely important mineral.

The earliest criers of calamity were usually content to bemoan a reckless squandering of natural resources with consequent impoverishment of future generations. Since the Day estimate of 1908, however, estimates of petroleum reserves, including fields and regions yet undiscovered, have been expressed with a numerical exactness connoting an altogether unwarranted degree of precision.. This quantitative definiteness seems to have inspired oil producers with unmerited confidence in the value of the estimates as indexes to the future.

Recent performances of the industry have not run with the estimates. Quite the contrary, the producer of petroleum recently found himself suffering from prices so low that many of his operations could be continued only at a loss; a condition which arose partly as a result of over-production and a glutted market both in the United States and Mexico. This happened at a time when he had every reason to expect, from the estimates of geologists and the conclusions based upon them by the most eminent and capable leaders of his industry, that petroleum would be in great demand and bring correspondingly high prices.

Even now his position is none too secure. Recent developments have opened up new fields both in the United States and Mexico which may result again in over-production and panic prices. Is it any wonder that the producer is somewhat bewildered by the present situation, disgruntled with the estimates he has received, and more than ever distrustful of geology and geologists ?

: & oe

EDITORIAL. 41 a It is now apparent, or should be apparent, even to the esti-

mators, that previous estimates have been too low, and that warn-

ings of an impending world shortage in petroleum have been

received with unmerited confidence in their correctness and in the

adequacy of the premises upon which they were based. Leaders

of the industry used them as bases for appea's to the operator to

exert himself vigorously in the development of new sources of : supply. Such appeals were the dominant note of addresses de- - livered as late as the November, 1920, meeting of the American

Petroleum Institute.

These addresses were hardly in print before calamity came upon the industry from a restricted market caused by industrial depression, curtailed exports, and over-production both here and in Mexico. Pipe-line runs. were being cut, drilling operations suspended, many of the smaller independent operators forced into bankruptcy or the hands of the larger companies, and thousands of men thrown out of employment. The market price for crude petroleum in the Mid-Continent, Eastern, anc Coastal fields was cut 50 per cent. in less than thirty days and the credit value of producing properties was almost destroyed.

In an address to the Kansas Oil and Gas Producers' Association at Independence, Kansas, on April 11, 1921, W. H. Gray charges that the "debacle of 1920" was brought about by "the prophets who had sung so sweetly to the producers about the world shortage in oil." He does not charge the leaders of the industry with intentionally misleading the producer, but believes that they "listened too attentively to statisticians and geologists who were predicting the world's failure in the supply of oil."

The president of the Mid-Continent Oil and Gas Association, in his open letter of July 14, 1921, to the President of the United States, fairly appraises the value of estimates as follows:

These estimates, except as they apply to the immediate confines of developed and producing lands, are valueless. One may guess, but there is no worthy basis for an opinion, much less an estimate, of the petroleum reserves under undrilled lands. Predictions of exhaustion of this country's supply have been made for thirty years or more, but year after

42 Editorial.

year new fields have been discovered until today we have the largest production in our history.

This inability to accept the estimates of geologists at par is not confined to producers of petroleum. The late Franklin K. Lane, in one of his reports as Secretary of Interior, expresses himself with a distinction, unintentional let us hope, between geologists and honest men, as follows:

Geologists have estimated and estimated, and they do not differ widely, for few give more than thirty years of life to the petroleum sands of this country if the present yield is insisted upon. And yet, there is so much of mystery in the hiding of this strange subterranean liquid that honest men will not say but that it will become a permanent factor in the world of light, heat, and power.

Even the director of the United States Geolegical Survey states that the estimates may be too low by 50 per cent. or even more.

Such is the situation at the present time when committees of the United States Geological Survey and American Association of Petroleum Geologists and various individuals at the behest of the Petroleum committee of the American Institute of Mining and Metallurgical Engineers are preparing to bring forth new estimates of our petroleum resources.

Many of the past estimates have proved to be radically wrong; generally the estimates seem to be of little or no value to the industry, and the making of such estimates at all has been attacked by the producer and but poorly defended by the geologist. It has now become the subject for editorial attack and the common butt for jests in trade journals.

It behooves the geologist to consider seriously the value of these general estimates which he presents from time to time as well as the adequacy of the bases which he may have for making estimates at all. One might even question the necessity and desirability of trying to make such general estimates. It is doubtful whether they have been of value or service beyond giving concrete expression to and thus providing for popular education in the fact that our petroleum resources are not inexhaustible.

The Day estimate-of 1908, the first of the quantitative estimates, was prepared under the auspices of the United States

act ' : :

Editorial. 43

Geological Survey in support of the campaign for conservation of natural resources. It gave a minimum of Io billion barrels and a maximum of 24™% billion barrels as the estimated total yield of the petroleum fields of the United States.

Some of the regional estimates upon which this general estimate was based have already proved to be worthless. The Mid- Continent region, for example, was estimated at a minimum of 400 million barrels and a maximum of one billion barrels. It has already produced approximately 50 per cent. more than the maximum estimate and is today producing at a rate higher than any previous time. The estimate of 282,875,000 barrels remaining capacity for the State of Oklahoma, even as a minimum, can only be considered as most striking evidence of the impossibility of satisfactorily estimating petroleum reserves over wide areas where much of the reserve must lie in undiscovered pools. Oklahoma has already produced approximately one billion barrels of petroleum in the 13 years which have elapsed since the estimate was made and is today producing at the rate of approximately 100 million barrels per year.

The Day estimate, however, with its broad spread between maximum and minimum, makes less pretense to exactness than any of the estimates which have followed it and is probably a fairer guess at the order of magnitude of our petroleum resources than are the subsequent estimates. :

Ralph Arnold, in 1915, presented, as a revision of the Day estimate, an estimate of the total] ultimate production of the United States, as 9,098,557,140 barrels. This estimate did not differ greatly from Day's minimum estimate of ro billion barrels, but there are considerable differences in detail. Estimates for California and the eastern fields were reduced, while other western fields, particularly the Mid-Continent fields, were increased © considerably to bring them into line with development subsequent to the Day estimate. The Day maximum of 24% billion barrels was apparently not given further consideration in this or subsequent estimates.

The United States Geological Survey estimates of February, 1916, give a total estimated petroleum content of the fields of

J. ae

44 Editorial.

the United States as approximately 11% billion barrels. This estimate differs slightly from that by Arnold, the Gulf Coast being increased by more than one billion barrels and various detailed new areas amounting in all to approximately 11% billion barrels representing apparently the " minor fields"' of the Arnold estimate at a slightly higher figure.

Revisions of this estimate have been presented from time to time by the Director or Chief Geologist of the Survey and, as announced in The Petroleum Resources of the World, the estimate "is subject to revision as exploration, including both the investigations by geologists and tests by the drill, goes forward, and it will be revised from time to time."

Geologists and engineers have made great advances during the past few years in the development of methods for estimating the petroleum content of developed or proven properties. The vearly productions of individual properties, calculated according to the best practice, sometimes show big differences from the actual production, but over large groups of properties this error seems to be compensating and the totals are checking up with surprisingly low percentages of error.

If estimates of this class for all of the proved oil properties in the United States could be combined, the resulting group estimate would doubtless be correct to within 5 or Io per cent. An estimate of this sort has never been made in the past and is not likely to be made in the future, since it involves the collection and correlation of data on a scale too great to be justified by the results obtainable.

Even if an exact estimate of the future production of the proven petroleum deposits of the United States were obtainable, however, an estimate of our entire petroleum resources would depend largely upon what is to be expected from fields yet undiscovered. Estimates of this unknown quantity which have been made in the past, are being made at, present, and will be made in future are but guesswork and, to my mind, their making is a futile performance. There is not enough exact data available to any man or group of men to give even a flavor of scientific accuracy to the estimates.

Editorial. 45

The estimates for a specific region, of two men equally competent as geologists and equally well informed as to the geology and petroleum development in that' region, may and do vary widely, yet these estimates pass through the hands of another man or group of men where still another guess is made before the result is given to the public.

All sorts of methods are used in arriving at the estimates. One geologist charged with supervising the estimates for a single important State, after getting together the estimates for various minor regions, wavered for- several months between limits as wide as X and 3 X in his estimates and finally, with a sigh of relief, hit upon the felicitous conclusion that the State would produce as much in the future as it had in the past. This conclusion, together with a touching confidence in the corrective ability of the law of compensating error, has been the foundation of large parts of past estimates.

On another occasion, an older geologist found a group of younger men in committee trying to estimate the future prospects of a large and important area. The deepest pessimism prevailed. The older man, feeling keenly that all past petroleum estimates had been too low, harangued his younger colleagues so successfully that they decided to increase considerably their previous individual estimates and then take an average. The optimist was also allowed to enter an estimate. His estimate was so large that it brought the general average up to abeut what he would have guessed if unhampered by the cooperation of faint hearts.

No one realizes the weakness of these so-called estimates better than the geologists who made them. It is a pity that we should have this weakness and the limitations of our ability to make estimates emphasized by the petroleum industry, and that our over-indulgence in the ages-old pastime of prophecy making should give further grounds for suspicion to the very considerable group of oil operators who have always doubted that any good could come to the industry from geology or geologists.

E. De GoLyer.

65 Broapway, New York City.

J :

Discussion

This department has been established by the editors in order to afford tc those interested in questions relating to economic geology an opportunity for informal discussion. Contributions are cordially invited either in the form of discussion of more formal papers appearing in earlier numbers or bearing upon matters not previously treated. Letters should be directed to the Editor, Sheffield Scientific School of Yale University, New Haven, Conn. The full name of the author should be attached to all communications.

The Zonal Distribution Of Ores.

Sir: In the editorial of the 'November number of Economic GEOLOGY, 1921, p. 474, and as stated in the first footnote, the

writer contributed in a somewhat modified form what had been.

originally read as a short paper at the first meeting of the Society of Economic Geologists, December, 1920. The title used at this meeting was " Additional Notes on the Zonal Distribution of Ores, outwardly from an igneous source "; and. in both instances experiences at Bingham Canyon were introduced with a brief statement of very similar relations earlier described by Billingsley and Grimes from the Butte, Montana, district. The discussion of the subject would have been fairer had cases been cited which had been still earlier described. The writer wishes to express regret that the following were not noted. This expression is especially due to J. E. Spurr, who published in Economic GroL- oGy in December, 1907 (vol. II., p. 781), his very valuable paper, "A Theory of Ore Deposition," and on p. 791 distinguished six zones of characteristic ores and vein minerals outwardly from the intrusive as follows:

1. The pegmatite zone, containing tin, molybdenum, tungsten,

etc.

2. The free gold-auriferous pyrite zone, with coarse quartz gangue.

'ag ¢ ay a b tl P P a fr ar

Discussion. 47

. The cupriferous pyrite zone.

. The galena-blende (galena usually argentiferous) zone.

. The zone of silver and also much gold, usually associated with highly mobile elements such as antimony, bismuth, arsenic, tellurium and selenium.

6. The zone of earthy gangues, barren of valuable metals.

& Ww

Later, in the August number of Economic GEoLocy, 1912, p. 489, Zone 4 was broken up into two, a lower blende zone and an upper galena zone, usually but not invariably argentiferous. Zones 3 and 4 of the 1907 paper are the samme as the ones cited by me from Bingham Canyon, and in the same order. Zones 1 and 2 and 5 and 6 are not present in the Bingham case described. The zones are again cited by Mr. Spurr in the paper on "Ore Deposition at Aspen, Colorado," Economic Gro.ocy, June-July, 1909, p. 318; and in discussing the veins at Tonapah, Nev., in Economic GEoLocy, December, 1915, pp. 701-762.

Others have corroborated these zones, notably B. S. Butler in the summary of his comprehensive work in Utah, published in the February-March number of Economic GEOLOGy, 1915, Pp.

In a broadly general way, Waldemar Lindgren presented to the Mexican International Congress in the summer of 1906 the valuable paper entitled "The Relation of Ore Deposition to Physical Conditions," published in Economic March— April, 1907, 105-127, in which the minerals are classified into Persistent Minerals, and Minerals Unstable in all Zones. These two classes being understood, five specific zones are established, pp. 123-124, and in the table, p. 125, seven are given as follows from below upward. Under each the characteristic minerals are checked.

1. Igneous conditions.

2. Pegmatitic conditions.

3. Contact metamorphic conditions. Deeper vein zone.

Middle and upper vein zone.

y

48 Discussion.

6. Lower ground-water zone (zone of sulphide enrichment). 7. Upper (oxidizing) ground-water zone.

The year following, in the October-November number of Economic GEoocy, pp. 611-627, W. H. Emmons published "A Genetic Classification of Minerals," with a still more elaborate series of tables, embracing practically all rock-making and veinforming minerals grouped in eight different zones. The deposits at moderate and shallow depths are separated into two, depending on the presence or absence of igneous rocks. The products of dynamo-regional metamorphism are grouped by themselves.

There are undoubtedly many other contributions at home and abroad which might be. cited, but we may state that all these earlier contributions are the natural results of the growing conviction, built up especially in the decade of the nineties, that ore deposits were largely the after results of igneous intrusions, the basic idea which put new life into their study. As phenomena, ores in igneous rocks, pegmatite veins or dikes, contact zones, veins at shallow, moderate or even considerable depths, and oxidized zones had been known for many years; but the accurate and characteristic groupings of minerals as determined on the basis of physical conditions began to receive close attention in the opening decade of the present century. The writer desires to express his regret that all the papers mentioned above were not cited in the editorial, and that thereby some very important and germane contributions were overlooked; but if the editorial should excite new interest, and should bring out in addition the applications of the conceptions of physical chemistry: and the further statement of what has been experimentally accomplished in the laboratory, its publication will perhaps be justified.

James F. Kemp. CoLuMBIA UNIVERSITY, New Ciry.

Victorian Gold Occurrences.

Sir: In Dr. Junner's account of the genetic aspects of Victorian gold occurrences, in Econ. GEox., vol. XVI., March, 1921, pp.

th

tu oc de fe re: g mi Tl wl 1] or th on dé Gz du Se mi : up of an

Discussion. 49

80-123, there does not seem to me to be a full appreciation of the wealth of experience that lies behind the Cornishman's dictum, " Where it is, there it is.' The peculiar eccentricities of occurrence of free gold in quartz are as "characteristic of the deepest mining as of the shallower depths, and are as essential a feature of the vein as any other structure that can be named. They are the result of primary causes which appear to be disregarded in the claim that rich surface outcrops and pockets of gold from the surface to 300 feet are likely to be due to secondary enrichment.

In summarizing his account of superficial ores, Dr. Junner says (p. 118) that in general there is no extensive downward migration of gold in solution in the western portion of Victoria. This is indeed truer than is indicated by his general account in which he has stated conspicuous examples of marked superficial enrichment occurred at Tarnagulla, Bendigo, and Maldon—three localities in this part of Victoria. At Bendigo a crushing from the Confidence reef of 3,035 ounces from 3 tons is quoted. No one acquainted with the history of early Bendigo mining will doubt that a 3-ton crushing is a well-picked crushing. Its grade is nothing more than that of normal specimen quartz—superficial or deep-seated. our years ago a parcel of nice specimens were obtained from the footwall of the 1,552-foot saddle reef in the Garden Gully mine, which, for curiosity, was put through the battery by itself. The result was that 56 pounds of quartz produced 70 ounces of gold—a rate of 2,800 ounces to the ton. Several tons of this class of quartz might have been obtained last year from the Constellation reef at a depth of 600 feet if the mining company had sought small picked crushings. It was more economical, however, to stope the cap stone for its full width of 18 feet and a height of 12 feet, which, even so, yielded up to several ounces to the ton. Throughout many inspections of the Constellation reef during its extraction I did not discover anything to indicate the presence of secondary gold.

If the extent of surface denudation had reached the present 600-foot level of the Constellation, a similar example to the Con-

A

2G

50 Discussion.

fidence reef could have been presented without any additional surface enrichment. The same could be said if the extent of surface denudation had reached the 1,500-foot level of the Princess Dagmar mine, or the 2,700-foot level in the Victoria quartz mine, or the depth of any other of Bendigo's richest saddle reefs. There can be no reason to doubt a similar occurrence of rich rock in the Poverty reef at Tarnagulla, 25 miles from Bendigo, while at Maldon the general characters of the gold shoots at the surface have also been repeated in depth. The Maldon gold shoots are characteristically short and rich, and while the Beehive mine, quoted by Dr. Junner, may have "obtained its gold from the surface down to 300 feet," other mines at Maldon, like the South German, obtained very little gold down to a depth of me feet, below which it was remarkably rich.

Surface enrichment may perhaps add to the value of outcropping gold shoots, but it does not account for their occurrence. The extreme richness of the Victorian alluvial gold seems, however, to indicate that there could be but an insignificant amount

of solution of gold during the surface denudation of former

quartz reefs.

Order of Deposition of Minerals——Dr. Junner has attempted to establish an order of deposition of the minerals in the quartz reefs based on the relation between minerals in certain specimens. The attempt is the outcome of the belief in the deposition in open fissures, to which Dr. Junner adheres. I have found gold at Bendigo forming the nucleus of one cube of pyrite and gilding the periphery of another cube of pyrite, so that one should conclude that gold is both earlier and later than pyrite. The same observations have been made with arsenopyrite and galena and blende, and considerable doubt should, therefore, be thrown on the existence of any definite order of deposition in these veins. The actual facts are more in accord with the "growth" theory

of vein formation in' which the vein is viewed as a slow and

steady growth, which indicates that no specific order can be expected in a vein. This can be clearly indicated by reference to the accompanying photographs of artificial copper sulphate veins

gol Jur mid

adn

hed

: ma 2 : 7 the son

Discussion. 51

(Figs. 8 and 9), formed in the manner described by Professor Taber.t. The CuSO, in the small intersecting veins in the later stage of growth was formed at a later date than the CuSO, in

Fic. 8. Exposed portion of a porous pot, inverted and immersed in a saturated solution of CuSQ,, as described by Taber, showing the development of veins of CuSO, after six weeks.

the initial vein. In the same way with quartz veins, the quartz may be continuously formed from the initial stages up to the final stages. The continuous deposition can also be pictured for the mineral constituents, so that in any growing aggregate of, say, gold and pyrite, some of the gold may be precipitated before some of the pyrite and some of the pyrite hefore some of the gold. This conception appears to me to be supported by Dr. Junner's descriptions of "boulangerite and gold ore intimately mixed and essentially contemporaneous," and of " gold intimately admixed with bournonite, arsenopyrite and occasionally tetrahedrite."

1" Growth of Crystals under External Pressure," S. Taber, Amer. Jour. Sci., 4th Ser., vol. XLI., 1916, p. 546.

52 Discussion.

Nuggety Gold.—Dr. Junner claims that certain nuggety gold in shallow depths in the eastern half of Victoria has been due to secondary enrichment, and attempts to extend the theory to the nuggety gold obtained in depth from the Ballarat field in the western portion of Victoria.

Nuggety gold is not characteristic of Bendigo, but the gold in spurry formations on this field is characteristically coarser than

inches

Fic. 9. Same as Fig. 8, showing the veins after three months.

the gold in the saddle reefs. Coarse shotty gold up to 4 inch in diameter is common in the spurs whose average width is about 6 inches, and I have seen 12-ounce fragments which have been obtained from the Victory spurs in the Carlisle mine. Most of the gold in the spurs occurs around their intersection with a bed or film of slate. In the richest spurs shotty gold is found extending into those portions of the vein bounded by sandstone. In the poorer spurs the gold is confined to .the intersections with slate. The occurrence of other minerals such as blende, pyrite and ankerite is noticeably similar. At the intersection with slate

: : REE ' J : q fi ti anes Se th d a CO so

Discussion. 53

the spur usually contains carbonaceous residues, which, in addition to the slate, help to precipitate the gold in this position from solutions percolating along the course of the vein.

If the conditions producing the localization of gold along a slate film were intensified so that the gold crystallized in fewer centers, the occurrence would appear to be similar to that of the nuggety gold at the intersection with indicators at Ballarat. Many spurs which intersect a particular slate film at Bendigo do not show gold at its intersection and many "makes" of quartz along an "indicator" at Ballarat do not carry gold. Each particle of gold in the Bendigo spurs is as much a part of the spur as any crystal of quartz, or any crystal of sulphide, and there is, in my opinion, no doubt that the gold in these spurs is primary, i.c., the vein formation was such as to localize the gold in this manner at the time the vein was formed. If this curious localization is an argument in favor of the secondary deposition of the gold, it could also be claimed that galena, blende, arsenopyrite and the other minerals similarly distributed in the vein are secondary. In fact, the conclusion would be drawn that the only part of the vein that is not secondary is the quartz, and even some of the quartz is deposited after the sulphides. Pushing this argument from localization to its logical conclusion would require a belief in the secondary origin of far more of the reef than Dr. Junner or any other exponent of secondary enrichment would probably find it convenient to entertain. The comparison of these conditions in the gold-bearing spurs at Bendigo with those at Ballarat seems to render it probable that the indicator gold of Ballarat is primary.

The Formation of a Nugget.—In any part of a growing vein the local conditions, such as temperature, pressure, rate of flow, degree of saturation and presence of precipitant, may be such that a particle of gold is deposited. Provided the conditions remain constant and the supply of solution is sufficiently slow and steady so that all the gold molecules in solution can be attracted to the single center of gold crystallization, the gold crystal will steadily grow and make room for itself and form a nugget. The final

h kaye:

54 Discussion. °

size of such a gold nugget will be limited only by the amount of solution supplied. The more nearly such ideal conditions are reached in nature, the more nuggety will be the gold in the reefs; and I picture them as having been reached in the cases of reports of isolated nuggets in large quartz reefs related to me by old miners.

It is more likely, however, that there would be a number of points in one locality where the deposition of gold commences and each of these will simultaneously grow until the supply of solution is checked. The fewer the centers the more nuggety will be the gold. Where carbonaceous precipitating matter is abundant, as in the Bendigo saddle reefs, the centers of crystallization and the individual gold particles will be small. Should the rate of supply be too rapid, these centers of growing gold crystals will not be able to extract all the gold from the passing solution and some gold will be carried along until another favorable locality is reached.

The amount and rate of supply of auriferous solution are therefore factors in the production of gold nuggets or gold shoots and, other things being equal, deposition is likely to occur where fractures enable the circulating solutions to have ready access to the reef zone. Such are the conditions that have already bee. pointed out? as obtaining around the intersection of a leg reef and fault at Bendigo, where enrichments are frequently known to occur. If, in such instances, the ideal conditions existed for the continued growth of a single crystal of gold, this type of Bendigo enrichment would be converted into a pocket of nuggety gold in the reef near the intersection of the fault. Such conditions appear to have obtained in the region of Dunolly; Rheola, etc., a district noted for its nuggety gold, 25-30 miles west of Bendigo. It is also notable in Dr. Junner's description of his secondary nugget® that the occurrence is near a fault plane and along the walls of a dike—a combination of circumstances which

2" Factors Influencing Gold Deposition in the Bendigo Gold Field," F. L. Stillwell, Bull. 4, Commonwealth Adv. Counc. Sci. & Ind., p. 55.

3" Geology and Ore-Deposits of Walhalla-Wood's Point Auriferous Belt."

N. R. Junner, Aust. Inst. Min, Eng., N. S., No. 39, 1920, p. 233.

:

? "Sipe A

it ( (

Discussion. 55

would tend to provide an abundant supply of circulating solu_ion and so permit the formation of a primary nugget.

The argument thus outlined is clearly independent of the dire:- tion of the circulating solutions and will apply whether they be primary solutions migrating upwards or secondary solutions migrating downwards. The argument, however, is general, and mineral sulphides or quartz can be pictured as forming in the same way, except perhaps that gold can be assumed to be precipitated more readily than other minerals on account of the general chemical instability of its compounds.

The reefs may contain not only nuggets of gold, but " nuggets " of pyrite, pyrrhotite, galena, sphalerite, and arsenopyrite. These sulphide "nuggets" occur with much greater frequency than nuggets of gold; but they do not happen to occur in the oxidized zone and in alluvial deposits, because they are less stable than

gold under the oxidizing influence of superficial solutions. No

one has suggested a secondary origin for these "nuggets" of the various mineral sulphides which occur in the gold-bearing reefs at all depths, nor does it appear to be reasonable to do so. Yet the occurrence of galena, sphalerite and pyrrhotite is characteristically similar to the occurrence of gold, and hence it seems most unlikely that the gold nuggets in the western Victorian quartz reefs are the result of secondary processes.

FRANK L. STILLWELL. BENDIGO, AUSTRALIA, Oct., 1921.

The Origin Of Graphite.

Sir: Without entering into any discussion on the graphite deposits which have been listed as of sedimentary origin, altered coal seams, etc. (classed by Clark, Econ. Grox., Apr.—May, 1921, as " Bedded Deposits"), I desire to express through your columns some remarks about graphite lodes which have come under my personal notice, together with some doubt as to the sufficiency of the chemical theories of the origin of graphite ad-

— 464

'

56 Discussion.

vanced to date, and some ideas which I have personally formed on the subject.

: In the Northern Territory of Australia in which I spent four years on geological investigations, shear zones and fissure lodes carrying varying amounts of graphite mixed with other lodeforming minerals are common. The Faded Lily Line of gold reef at Brock's Creek is a case in point. It is a quartz reef occupying part of a shear zcne with chlorite, actinolite, garnet, epidote, graphite and iron pyrites in sericite schist, andalusitesillimanite rock, felsite, and quartzite. The Zapopan lode at Brock's Creek is highly graphitic and pyritized. The Iron Blow lode at Yam Creek is a highly pyritous ore body with graphite, and the Mt. Ellison Copper Mines were also graphitized lodes. In fact in the Northern Territory mineral fields, which are all in Pre-Cambrian formations, graphite is a common mineral in most shear zones and fissure lodes.

It was observed by myself as well as by my colleagues, Messrs. Winters and Gray, that, as far as the Territory fields are concerned, lode graphite is almost invariably associated with mundic (iron pyrites) in the most intimate manner, so much so, that in a manuscript which I wrote, but which was not published on account of war retrenchment, I advanced the theory that iron was concerned in the origin of lode graphite.

The Brock's Creek District in the Northern Territory is, however, an area in which there is a great development of lime silicate rocks. on and near graphitic contacts; sillimanite, zoisite, scapolite, andalusite, chiastolite, fibrous hornblende and garnet are all common rock-forming minerals in this region, and some of the andalusite schists are highly graphitic. A chiastolite schist from the Margaret River analyzed 11.10 per cent. carbon. Probably these graphitic lime-silicate rocks are derived from limestone or mixed carbonate rock, and the heat of the granite has driven off carbon dioxide which, under conditions of great

heat and pressure in the presence of magmatic waters, has inter-

acted with sulphuretted hydrogen and with sulphur depositing

&

pee

'

( ( f Ss a p a

Discussion. 57

carbon. These reactions might be stated in the following getieral equations:

M.CO;= M.0 + CO., ; M.O+ SiO. (from magmatic solutions) M.SiO, (silicate rocks), 2CO. + H.S=H.0 + SO.+ C, and similarly for MCO,; and M.(COs;)s.

During geological survey work in North Queensland it was observed that shear zones and fissure lodes in the Pre-Cambrian of this State are also strongly graphitized.

At Croydon Goldfield, North Queensland, great flat shear zones, which dip at angles of 30° and less, intersect granite. The sheared zone is composed of rounded granite boulders (of crush breccia derivation), and an interstitial mixture of quartz, pyrite, and graphite. The granite boulders are often quite smooth and coated with graphite. In some places quartz is almost absent in the lodes, which then consist of a dense mixture of pyrite and graphite.

There is no doubt in my mind that the Croydon shear zone graphites are like the Territory graphites, of pneumatolytic (hydato-igneous) origin. Some previous writers leaned to the fantastic and crude theory that the granites of Croydon are metamorphic granites, in fact, metamorphosed sandstones, and consequently the graphite lodes were put down as metamorphosed coal seams of Gympie age. Obviously such could not have been the case, otherwise the original coal beds would have been puckered and bent in the movements of the viscous mass, whereas the Croydon lodes are flat sheets.

I have examined sections of both the so-called "metamorphic" granites of Croydon and of the mass supposed by Rands and others to be later. I found no mineralogical differences of sufficient importance to allow any petrologist to pronounce the one granite of metamorphic, the other of igneous origin. In fact all slides were typical igneous granites which had under-

fe

a

58 Discussion.

gone a considerable amount of alteration. There was no indication of sedimentary origin. There may or may not be two periods of granitic intrusion represented in the Croydon mass, but that does not affect the issue.

My opinion is, that graphite is deposited pneumatolytically from iron carbonyl which is produced by the interaction of metallic iron with carbon monoxide under conditions of high temperature and pressure. As carbon dioxide under those conditions dissociates into carbon monoxide and oxygen, and carbon dioxide is an invariable emanation of cooling magmas, it is obvious that the molecules required for the formation of carbonyl

compounds are present. Further, the temperature-pressure con-.

ditions of cooling granite magmas are those requisite for the formation of carbonyls. Iron, nickel, chrome, and molybdenum form carbonyls readily when carbon monoxide is passed over the metal heated to over 450° C. under 500 atmospheres of pressure. In hot cooling magmas it is reasonable to suppose that many of the metallic constituents exist in the ionized form.

The carbonyls of iron are mostly clear oily liquids soluble in petroleum and insoluble in water, but decomposed by moist hot air with the production of metallic iron hydroxide and carbon monoxide. They are unstable volatile compounds and under slightly varying conditions decompose spontaneously yielding different products; thus iron carbonyl may yield iron and carbon monoxide, or iron oxide, carbon dioxide and carbon (graphite). The peculiar properties of the carbonyl compounds are utilized in metallurgy in the Mond process for the extraction of nickel.

Sulphur and oxygen are chemical equivalents and yield similar compounds with the . etals, hence it is probable that under the temperature-pressure conditions existing in cooling magmas, thiocarbonyls would also form and would pass away in the gaseous form, and as the temperature and pressure conditions change, deposit pyrite and graphite, thus:

FeS, 2C, or FeS, CS; + Ge

Some carbonyls on contact with moist air yield metallic carbonates and hydroxides and CO.

bY ig :

Discussion. 59

The latter under conditions of relieved temperature and pressure may yield carbon dioxide and carbon.

The CS. formed in the decompositionsof the thio-carbonyls would form thiocarbonates. Carbonates are high temperature compounds. Thiocarbonates are probably also formed under high temperature conditions. They tend under normal conditions to decompose into metallic sulphides and CS.. However, K.CS,, a thiocarbonate of the polyvalent potassium, decomposes into K.S,;-+C. As iron is also poylvalent it is possible that its thiocarbonate will behave similarly, yielding pyrite and graphite.

Consequently without disputing the possibility of the oxides of carbon disintegrating with the production of graphite under certain conditions as supposed by Alling, Clark, and others, I venture to suggest that the reactions which actually take place in nature are connected with the formation of carbonyls and thiosulphates of iron and their subsequent decomposition. That is at least suggested by the field evidence in the regions examined by me where pyrite (and sometimes sulphur as well) is asso- ° ciated with graphite.

H. I. Jensen.

Geological Survey Department, Brisbane, Queensland.

@

Reviews

Economic Aspects of Geology. By C. K. Lerrnm. Henry Holt and Co.,

New York, 1921, 457 pages.

The title of this book has been carefully chosen, for in it are set forth the distinguishing characteristics of economic geology, particularly at this time. It is a study of the status of the science supplemented by pointed inquiries as to its future.

"It is proposed . . . to discuss the economic aspects of geo'ogy without exhaustive discussion of the principles of geology which are involved. ... Our purpose is rather to indicate and illustrate, in some perspective, the general nature of the application of geology to practical affairs."

The peculiar value of the book lies in the breadth of view of the author and the successful assembling in one volume of so many related subjects. Although the author makes no pretentions to originality in subject matter, yet independent solutions of various problems involving theoretical and practical matters are either set forth clearly or indicated. Thus the reader throughout is influenced by the carefully considered judgment of the writer. The text naturally falls into three subdivisions, although the book is not thus set up in type. The first part, Chapters I. to IV. lay the foundation for what is to follow. The common elements, minerals and rocks and their origin are discussed in Chapter II. The subject matter is clearly stated. The laymen may reaa it with profit. All the essentials are present.

Then follows in Chapter III. a classification of mineral deposits and a discussion of their origin. This chapter has the peculiar value of stating in plain language a number of unsolved problems. There is an introductory statement, regarding classification in general which, in pointing out the dangers of rigid classificatory systems, clarifies this subject. The actual classification which follows is based on widespread, fundamental, and distinct geologic processes, and therefore is easily comprehended and kept in mind.

These processes are three, (1) after-effects of igneous intrusion through the agency of aqueous and gaseous solutions given off from cooling magmas; (2) sorting processes of sedimentation; and (3) weathering of the rock surface in place.

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Reviews. 61

It is interesting to note that "the overwhelming preponderance of values of mineral deposits as a whole is found in the second of the classes named."

Chapter IV. surveys some important quantitative considerations from the "tonnage" and "value" standpoint and is accompanied by a useful diagram of political and commercial control of raw mineral resources.

With these data as a background the book through Chapters V. to XIII. is descriptive of the various mineral groups. These are carefully chosen and emphasize their commercial aspects. Thus, Water, Common . rocks and soils, Fertilizers, Energy Resources (coal, oil and gas), Iron and Steel, etc., are in turn considered. In each case both the geologic and economic features of the minerals are separately presented. The treatment is brief but comprehensive and the author is to be congrat-' ulated on so succinctly stating so much useful information. Only essentials are given, but these are in no instance wanting.

The third part of the volume reflects the long experience of the author in practical affairs. The reader is given the benefit of his judgment, but nowhere is personal opinion insistent. Rather one is in part led to adopt his view because of its modest presentation. Exploration and Development, Valuation and Taxation, Laws, Conservation. International Aspects and Minerals, Geology and War, Geology and Engineering and finally The Training and Ethics of the Economic Geologist each receive a chapter. Facts, not theories, are mainly considered; results are emphasized and tendencies indicated.

Some of this portion of the book is based on the experience of the author during recent years, partly in Europe. The following statement concluding the chapter on International aspects of minerals is typical: "Tt is our purpose to bring home the fact that international cooperation in the mineral fields is not merely an academic possibility but that in many important ways it is actually in existence. . . ."

The book closes with a thoughtful! discussion of the training, opportunities and ethics of the economic geologist. It is gratifying to the reviewer that Professor Leith so clearly emphasizes the need for broad academic and geologic training as a groundwork for the econom:c geologist of tomorrow; a mere specializing in metals or oil or coal will not nor cannot make a geologist of attainment. This will become increasingly evident as time goes on. The reviewer cannot imagine a more limited field than that occupied by the hastily trained geologist. Students may read carefully and weigh with profit the last chapter of Professor Leith's book.

All those even remotely interested in the commerce of raw minerais

¢

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62 Reviews.

or in policies, private or public, respecting such materials will derive profit from the volume. : SIDNEY PAIGE, U. S. SuRvEY, Wasuincton, D. C.

The Tin Resources of the British Empire. By N. M. PEnzer. William Rider and Son, Ltd., London, 1921, 358 pages.

The book is the second of a series on " The Raw Materials of Industry," edited by J. S. M. Ward. The first volume dealt with cotton and wool throughout the world. This volume deals only with tin obtained within the British Empire. This restriction seriously impairs its value and in part defeats one of the purposes of the series set forth in the general introduction by the editor. He says "unless full and detailed information is obtainable on such important raw materials as tin, it is ludicrous for statesmen to attempt to formulate an economic policy." Even though the British Empire produces two thirds of the world's tin, a sound economic policy for the development of its own resources cannot be formulated if the resources from which the remaining one third of the production comes are left out of consideration. A second volume is promised, conditional on the demand for this volume indicating sufficient interest in the subject, which will deal with the tin production of-the rest of the world. A series of volumes of this sort ought to be balanced, however; and it seems that if " full and detailed information " on cotton and wool of the world could be included in one volume, equally full and detailed information on the tin resources of the world should not require 'more space.

The volume is the second British publication dealing with tin issued since the Great War, both of which are the outgrowth of information

collected in connection with national inventories of war minerals. In ©

1919, the Imperial Institute issued a 111-page volume on " Tin Ores' by G. M. Davies, as one of a series of monographs on mineral resources. It deals with the tin ores of the world, but in very abbreviated form. The volume by Penzer is a fuller treatment of the tin ores of the British Empire. Both books lack the broader point of view represented in the chapters of Spurr's " Political and Commercial Geology." The chapter on tin in that volume tells nothing of individual deposits, but it does give a good picture of the political and economic role of tin throughout the world. Penzer's volume merely describes the tin deposits of the British Empire, and it fails to give a picture of their role in the world's politics and economics. It is, of course, an author's right to

My

Reviews. 63

determine what he will write about, and the "Tin Resources of the British Empire " is a big enough subject to write a book about. But the book would have been so much more interesting and valuable, if some detail had been omitted to permit of widening itS scope to include the other third of the tin production and a world view of the tin industry, that I feel it the privilege of a reviewer to make this comment without prejudice to the merit of the volume in the field the author has chosen to cover.

With a book of this type, which is primarily a presentation of descriptive and statistical data, the reviewer can do little more than tell what its contents are. The book is divided into nine chapters. An introductory chapter is followed by five chapters on Europe, Asia, Africa, America, and Australasia, respectively. Then come chapters on the industrial applications of tin; prices, sales of tin, and world's output ; and a bibliography.

Chapter 1 is divided into two sections. The first section bears the misleading title " Brief Historical Sketch of Tin Production:" It is ai four-page discussion of the etymology of the word tin and the sources of the tin used by the ancients. The second section devotes seven pages to brief descriptions of the tin minerals.

Three pages of Chapter 2 deal with Scotland and Ireland and thirtythree pages with Cornwall and Devon. Traces of tin have been found at several localities in Ireland. The only occurrence of tin in Scotland, in East Ross, presents unusual geologic features. Cassiterite occurs as a subordinate constituent of black streaks and lenses of magnetite irregularly distributed in bands of gray albite gneiss in a fine-grained reddish granite gneiss. The gray gneiss is garnetiferous and grades through an intermediate zone a yard wide into the red gneiss. The magnetite lenses and streaks are generally slickensided, but in one band the marginal parts interlock with feldspar and are bordered with scattered grains of the black ore. The probability of the garnetiferous albite gneiss representing an unusual type of basic segregation is suggested.

The production of tin in the British Isles has been confined to Cornwall and Devon, and amounts to 5,000 to 6,000 tons of concentrates annually. The Devon output, never large, now is only % per cent. that of Cornwall. Ten pages of tables give the output of the individual mines, and the imports and exports of tin ores and tin between the British Isles and the rest of the world. The Cornwall district is an old one, and the productive mines have all been working over fifty years. The Dolcoath mir: has been the leading producer for sixty

st j

64 Reviews.

years and is the deepest mine in Cornwall. A short account of the geology of the region accompanied by a map showing the location of the principal mines and a generalized geologic map of the Camborne region is followed by descriptions of the mines of seventeen companies. Lower Devonian to Lower Carboniferous shales, called killas, were invaded by basic dikes and volcanic flows, called blue elvans, and later folded and faulted by crustal movements. The intrusion of granites into these rocks marked the culmination of a long series of earth movements. The consolidation of the granite was followed by the intrusion of dike rocks, of which quartz porphyries, called elvans, are the most important. Their direction is more or less parallel to the major lodes as both followed lines of cleavage and fracture. Gaseous and hydrothermal emanations constituted the final stage in the consolidation of . the magma. They altered both the granite and the killas, converting the granite into schorl, a quartz-tourmaline rock, into greisen, and into kaolin, and tourmalinizing the killas near fissures. Their metallic content was deposited in lodes in the granite and in the killas near.the granite contacts. The earliest mineralization was of tin and copper. Over a wider area and later, lead and silver lodes were formed. The descriptions of the individual companies are brief notes on their holdings, developments, and their lodes.

The big chapter of the book is the one on Asia. Four geographic divisions are raade—Malaya, Indian Empire, Ceylon, and Hong Kong. On the mainland, opposite Hong Kong Island, are unimportant tinbearing alluvial deposits. But Hong Kong is a center for the smelting and refining of Chinese tin, especially that from Yunnan. There are five refineries at Hong Kong. Cassiterite has been found at a number of localities in Ceylon, but never in quantity to suggest the presence of workable deposits.

Sixty-eight pages are devoted to the discussion of the tin industry of Malaya. The section includes a map of the Malay Peninsula showing the locations of the tin-bearing areas, two geologic sections across the peninsula, and several photographs illustrating the methods of working the deposits. The Malay Peninsula consists of a number of granite and quartzite ranges. The main granite range lies well towards the west coast. West of it are smaller granite ranges and scattered granite hills. In the Benom Range, east of the main granite range, is more basic hornblende granite and some syenite, in association with which are no tin deposits. East of the Benom Range is a broad belt of quartzite which forms Mount Tahan, 7,186 feet high, the highest mountain of* the peninsula. Toward the east coast acid granite is again encountered. The granites appear to be of late Mesozoic age. The quartzites, with

REVIEWS. 65 which are associated also phyllites, are shallow water deposits of Mesozoic age. Another series of rocks into which the granites have been intruded, called the Raub series, are Carbonifergus and Permian in age. This group includes massive limestones, shales, and schists. It has associated with it a widely developed series of contemporaneous volcanic rocks, the Pahang volcanic series. All of the sedimentary rocks have been strongly folded and faulted, and the Main Range and Benom massifs occupy two broken plicated anticlines. The tin deposits are closely associated with the granite intrusions and hence are most abundant in a belt which includes the Main Range, though there are productive districts along the east coast also. Lodes have been worked to a limited extent, but of greatest importance have been the alluvial deposits. Many of the so-called alluvial deposits are, however, eluvial, representing the soft weathered outcrops of tin-bearing rock. Besides the more abundant alluvial and eluvial deposits and the less important lodes in granite, two other interesting types of tin deposits occur. At a number of localities detrital tin ore is found in limestone caves and in underground streams. The second unusual mode of occurrence is as pipes in limestone, in the State of Perak, in the Kinta and other districts. The ores in the pipes are notable for the abundance of metallic sulphides associated with the cassiterite and the rarity of tourmaline.

Mining in Malaya is carried on by ground sluicing and hydraulicking, open cut workings, underground workings, and dredging. Though dredging was first inaugurated in 1912, there are now 16 dredges in operation. Over 70 per cent. of the tin output comes from Chinese owned and Chinese operated mines. The success of the Chinese has lain in cheap labor, small operations, and simple, inexpensive equipment, which give a high degree of mobility so that they can quickly and cheaply try out any locality and abandon a locality as soon as it is no longer profitable to work. About 225,000 Asiatics are employed in the tin mines, of which about 75 per cent. are Chinese. The combined output of the Straits Settlements and the Unfederated Malay States is only 10 per cent. of the Malayan production. Johore is the only unfederated state with a considerable production—about equal to that of Pahang. Over one half of the Malayan production comes from Perak and over one fourth from Selangor. The other two federated states in order of productivity are Pahang and Negri Sembilan. The Straits Settlements possess the largest tin smelting and refining industry of the world, centered at Penang and Singapore, which together receive 80 per cent. of the Malayan output. The entire Malayan production is equivalent-to about 2,000 tons of concentrates annually.

The tin deposits of the Indian Empire occur in Bengal, Bombay, ana

66 Reviews.

Burma. Those of Bengal and Bombay are not of economic importance. Those of Burma are found in four districts which from south to north are Mergui, Tavoy, and Thaton along the Bay of Bengal in Lower Burma, and Karenni in Upper Burma. The entire output is equivalent to less than 1,000 tons of concentrates annually. During the last decade Tavoy has been of much greater importance as a producer of tungsten ores.

Western Burma consists of Tertiary and Quaternary rocks, eastern Burma of .gneisses and Paleozoic rocks. The tin deposits all lie in eastern Burma; and Tenasserim, which might be called the inner end of the Malay Peninsula, where most of the tin mines are located, has yielded Carboniferous fossils. The principal hill ranges of Tenasserim consist of discontinuous series of granite bosses traversed by quartz porphyry and pegmatite dikes, which have intruded a group of schists, slates, and sandstones. 'The tin is invariably found near the granite hills. In Mergui it occurs under four conditions: (1) As a constituent of decomposed pegmatite rich in tourmaline and muscovite; (2) In massive quartz segregations which also carry wolframite, pyrite, and chalcopyrite; (3) In quartz veins and stringers adjacent to pegmatites; (4) As hillside talus and alluvial accumulations in streams and flats. In Tavoy the modes of occurrence of the tin ore are similar, except that much of the placer tin was probably derived from cassiterite occurring as an accessory constituent in the granites. The Thaton district is a recent discovery, but the occurrence of tin is similar to that in the other two districts. The Karenni deposits seem also to be like those of Tenasserim. Only a little lode mining has been done in Burma, and most of the production has come from the detrital deposits. The mining is largely in the hands of Chinese and Siamese, and conditions are analogous to those of Malaya.

Six British possessions in Africa contain tin deposits—Nigeria, Gold Coast, Nyasaland, Union of South Africa, and German Southwest Africa. Only Nigeria and the Union of South Africa have an appreciable production. High-grade coarse alluvial cassiterite was found on the Gold Coast, west of Winnebah, a few years ago. Prospecting re-- vealed a country of garnetiferous hornblende schist with northeast strike, intersected by coarse-grained pegmatites and other dikes carrying cassiterite. To the southeast are large areas of granitoid rocks. The same geologic formations extend eastward to the boundary of Togoland. Associated with the cassiteritie in the pegmatites is tourmaline, molybdenite, scheelite, and other common associates of tin. A small amount of cassiterite has been found in river sands from Nyasaland. The chief occurrences of Rhodesia are in the Enterprise District near Salisbury

Ape ry

Reviews. 67

and about 30 miles east of Victoria. In both localities intensely folded metamorphic groups, called the epidiorite group and the banded ironstone group, are surrounded on three sides by granite. Both the metamorphics and the granite are cut by pegmatite dikes. Those in the metamorphics are frequently greisenized and carry cassiterite. In German Southwest Africa cassiterite occurs in dikes and lenticular masses of pegmatite intrusive into ancient schists of the Orongo Mountains and the area to the northwest of them.

About three fourths of Nigeria is underlain by a crystalline mass of granites, gneisses, and schists. The tin deposits occur on the Bauchi Plateau and in the Nassarawa area southwest of it, a region which lies north of the Benue River and east of the Niger River. The granite of the Bauchi Plateau was decomposed to great depth in former time. then came the formation of the plateau and the disintegration of the decomposed granite which was washed from the higher ground and spread over the plateau as the alluvial deposits which carry the cassiterite. Most of the Nigerian mines are located on such deposits. in the Nassarawa District is a 45-mile, southeasterly trending belt of pegmatite and greisen that contains cassiterite. Most of the work has been on eluvial and alluvial concentrations of this cassiterite. The annual Nigerian output is about 8,000 tons of concentrates, and is produced by dredging, ground sluicing, etc.

In the Union of South Africa, tin occurs in the Transvaal, Cape Province, Natal, and Swaziland. The Waterberg district, in the northwestern Transvaal, produces about 3,000 tons of tin concéntrates annually. The tin deposits occur in the Lower Waterberg felsites and shales and quartzites and in the red granite of the Bushveld Plutonic Complex. In the red granite the deposits occur (a) in roughly cylindrical pipes; (b) associated with irregular bodies of altered granite; (c) as impregnations along well-defined lines of fissure; (d) associated with pegmatite and quartz veins. In the Lower Waterberg rocks, the deposits are found in lodes and irregular pockets. The Swaziland deposits occur in the northwestern part and consist of alluvial deposits at Embabaan and lodes at Forbes Reef. The alluvial deposits rest on granite floor, but the cassiterite seems to have been derived from pegmatites and quartz veinlets in the granite. The Forbes Reef veins occur in the Swaziland quartzites and schists which are intruded by the same granite as at Embabaan. Swaziland produces about 500 tons of tin concentrates annually. The Cape Province and Natal occurrences are not of economic importance.

In America tin has been found at a number of localities throughout Canada but not in commercial quantities.

©

23

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68 "Reviews.

Tin has been found in all of the major political divisions of Australasia. A few hundred tons of concentrates are produced annually in the Greenbushes District in the southwest corner of Western Australia from alluvial and eluvial deposits derived from tin-bearing granite and veins. The Pilbara field in the northwest part has a small production ot placer tin. One or two hundred tons of concentrates are secured arnually from several districts in the northern part of the Northern Territory of Australia. The deposits are mainly cassiterite-tourmaline and chlorite-cassiterite veins and greisen associated with granites intruded into pre-Cambrian metamorphic rocks. South Australia produces no tin. Queensland has an output of over 1,000 tons of concentrates annually. Most of the production comes from the Herberton, Kangarov Hills, and Cooktown fields in the northern part of Queensland, but Stanthorpe in the southeastern corner is an important field also. These deposits are all intimately associated with granites and consist for the most part of veins in granite or graywacke and slate. Part of the production is won by sluicing and dredging. Tin deposits occur at many points throughout New South Wales, but the bulk of the production comes from the Tingha and Emmaville fields in the northwest corner, adjoining the Stanthorpe field of Queensland. Over half of the 2,000 tons of concentrates produced by New South Wales comes from placer deposits that are largely worked by dredging. About 100 tons of concentrates are produced annually from a number of districts in the eastern half of Victoria, where the primary deposits are stanniferous pegmatites, greisen, and quartz veins.

The Island of Tasmania is the largest tin-producing region of Australasia, the annual output amounting to nearly 3,000 tons of concentrates. Most of the tin deposits are grouped in two regions, in the northeastern and northwestern parts of the island respectively. The output from the districts in the northeast is chiefly from detrital deposits. The latter have been derived from tin-bearing quartz veins, greisen dikes, and greisenized marginal facies of granite masses. The northwestern region includes the two well-known Mt. Bischoff and Mt. Heemskirk areas and is chiefly a producer of lode tin ores.

The known occurrences of tin in New Zealand are chiefly of stream tin, and none have been proved of commercial value.

Chapter 7 is a four-page account of the industrial applications of tin. Chapter 8 devotes six pages to the prices, sales of tin, and the world's output. The discussion of sales of tin is an explanation of the Cornish Ticketings system.

Chapter 9 is a geographically divided bibliography with a chronologic arrangement under each geographic division. It covers the period since

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Reviews. 69

1910, reference being made for the period prior to 1910 to the excellent " Bibliography of the Geology and Mineralogy of Tin" by Frank L. Hess and Eva Hess.

As a popular account of the tin-mining industry of the British Empire, the book contains a great deal of useful and interesting information. It is of little value as a scientific or technical treatmcat of the subject. The geologist especially will be disappointed by the scarcity and vagueness of the geologic information. The framework of the book is Davies's " Tin Ores." Quotations of descriptions and production tables are freely used from it, without a consistent effort to complete the latter to the later date that might be expected of a book published two years after it. There is also not much balance or proportion in the material introduced. For some districts much geologic information is given, for others none; for some a full account of mining methods is given; for some much detail concerning companies' operations is included, for others none. The impression one gets is that there was no well-corceived idea of the kind of information that would best accomplish the purpose of the book and no effort made to compile such information, but for each region the information that was most easily available was introduced without selection or digestion. The number of maps is inadequate, and little or no attempt was made to place names used in the text on the maps. Lack of headings to tables of statistics is a source of annoyance and inconvenience to the reader. In all fairness, one can say that the volume is not one whit better than the Imperial Institute's monograph, contains very little more recent data, and consequently adds little to the knowledge imparted by that monograph. A 1921 volume as thorough as Sydney Fawn's " Tin Deposits of the World" would have come much nearer accomplishing the purpose of presenting "accurate

information" upon which statesmen could "formulate an economic

policy." Joseru SINGEWALD, JR. Handbook for Field Geologists. By C. W. Hayes. Third edition, re-

vised and rearranged by SmpNEy Paice. John Wiley & Sons, Inc., New York, 1921. Price $2.50.

This useful manual, which was originally prepared by Dr. Hayes for the guidance of geologists of the U. S. Geological Survey and which, in modified form, has gone through two unofficial editions, has now appeared in a third edition, thoroughly revised by Mr. Paige.

Among the important additions and changes noted may be mentioned the insertion of considerable new matter relating to the determination

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70 Reviews.

of the thickness of beds and the depth of any particular bed below a given point on the earth's surface. Three ingenious diagrams devised by Mr. J. B. Mertie, Jr., for the graphic solution of these problems should prove valuable, particularly to geologists engaged in oil and coal work. They have been reproduced on too small a scale, but fortunately will be available in clearer form in a forthcoming publication by the U. S. Geological Survey.

The section on the use of the plane table by geologists has been rewritten and now contains references to the principal papers that have dealt with the subject in recent years.

A section on the investigation of oil and gas fields has been added, but is too condensed and in some other respects not entirely satisfactory. The preparation of maps in which geologic structure is shown by contours drawn on the surface of some selected bed is briefly referred to and two small diagrams are presented on page 119 to illustrate the construction of such maps. These are reproduced on so small a scale, however, as to be scarcely legible and, even when deciphered, are not illuminating. It is very doubtful whether a young geologist wishing to know how to prepare a structure-contour map would get much help from this section. The subject is much more clearly treated on pages 34-38 of Warner's "Field Mapping for the Oil Geologist," recently issued by the same publishers. By omitting the cut and description of the topographic sketching case on pages 52-54 space might easily be made in a future edition for the improvement here suggested.

The schedules intended to guide the observer in recording data concerning various kinds of geological investigations, instead of being grouped together near the end of the volume, as in previous editions, have been distributed so as to follow, wherever practicable, the general treatment of the subjects to which they respectively pertain. This is clearly an improvement. The appendix giving the list of official geological surveys, with the names of their directors, has been brought up to date.

A new appendix has been added in the form of an excellent condensed text on mineralogy by Esper S. Larsen.

The book is of convenient pocket size, slightly narrower and taller than the second edition, and is similarly bound in a substantial leather-like fabric. with flexible covers. Hayes's Handbook is so well known and has so thoroughly established its usefulness as to make any additional comment unnecessary.

F. L. Ransome.

j q

Scientific Notes And News'

C. K. Lerru, of the University of Wisconsin, sailed for Chile, January 7th, for geologic examination.

H. S. GALE sailed in December for Colombia, where he will be engaged for three months in an oil investigation for an American company.

WALLACE LEE has been appointed Chief Geologist to the Government of Siam. His address is in care of the Commissioner General, Royal Railroad Department, Bangkok, Siam.

W. H. Rei recently examined the Paymaster Mine in the Porcupine District, Ontario.

ALFRED H. Brooks delivered an address on Alaska and its resources before the Algonquin Club, Boston, Mass., in January.

W. L. CuMMINGs, geologist of the Bethlehem Steel Company, sailed on the 7th of January for Coquimbo, Chile. He will be in South America about three months.

M. R. CAMPBELL, of the U. S. Geological Survey, left for Sanford, N. C., on January 19th, to do geologic work in the coal field of the State in cooperation with the North Carolina Geological Survey.

ErNEst Howe recently returned from Grass Valley, California, and is again living in New Haven, Conn.

H. A. Brouwer, Professor of Geology at Delft, Holland, particularly known because of his structural geology work in the

Geologists, mining engineers and others interested in applied geology are invited to keep the editor informed of new investigations of mining districts or scientific studies undertaken by them, together with such other scientific and personal items as may come to their notice.

72 Scientific News And Notes.

Dutch East Indies, is arriving in this country in early February to be exchange professor at the University of Michigan. He will deliver a lecture in Washington on the major tectonic features of the Dutch East Indies before proceeding to Ann Arbor. A contribution by him on the relation of structure to petroleum in the Dutch East Indies will appear later in this Journal.

G. R. MANsFIELp, of the U. S. Geological Survey, left January 19th for Porto Rico, where he will examine reservoir sites in connection with irrigation projects for the Porto Rican Government.

3AUER AND CLARK, Consulting Geologists, have dissolved partnership. Mr. C. Max Bauer is now in charge of the geological department of the Mid-Northern Oil Company with headquarters at Billings, Montana. Mr. R. W. Clark is doing consulting work at Okmulgee, Oklahoma.

Joun C. SEMPLE has left the firm of Armstrong & Semple, Spokane, Washington, and has opened offices for the practice of mining engineering in the Shoshone Building, Wallace, Idaho.

FRANK M. Estes, who has recently been in Central America, is now in Madera, Chihuahua, Mexico, where he will take charge of the Dolores mines.

CHARLES ScHUCHERT, of Yale University, was elected President of the Geological Society of America for 1922.

Joun T. Ret, who was recently in San Francisco, has departed from his office in Lovelock, Nevada, for New York, to be absent some time.

How1anp Bancrort has been elected a vice-president and director of the Sinclair Panama Oil Corporation.

PF. L. STILLWELL has resigned as geologist to the Bendigo Amalgamated Goldfields, Ltd., and is on a visit to South Africa, North America, and London.

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Scientific News And Notes. 73

Tuomas L. Reap has been appointed by the Secretary of the Interior to the Executive Committee to coOperate with the Commission in preparation for the U. S. Exhibit at the Brazilian Centennial Exposition in Rio this September. He will be interested in the mining exhibit of the United States.

J. MackintosH BEtt is in London.

PAuL BILLINGsLey, of the International Smelting Company

at Salt Lake City, has been in central Idaho inspecting mining properties.

Cuunc Yu WANG, consulting mining engineer and geologist, ' is with the Chinese delegation to the Conference on Limitation a of Armaments as one of the Technical Councillors. ;

ie FE. T. MELLor, of Johannesburg, South Africa, writes that he

i expects soon to entertain Prof. R. A. Daly, of Cambridge, Mass., and party.

e, A CoaL Bureau has now been established by the Natural

of Resources Production Department of the U. S. Chamber of

oO. Commerce under the direction of C. T. Starr. The new bureau will compile data and information about coal production and

consumption.

ee

J. H. Stover has been appointed Manager of the Mining Department of the E. J. Longyear Company, Exploring Engineers,

of Minneapolis, Minn. i At the Amherst Meeting the Society of Economic Geologists elected as officers for the following year: President, Waldemar Lindgren; Vice-president, Ralph Arnold; new councillors, James F. Kemp, C. K. Leith. and digo

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