The phosphate deposits of Florida ..

Matson, George Charlton · 1916 · Historical

The phosphate deposits of Florida .. by Matson, George Charlton (1916). Full text and reference in the Mountain Man Mining Library.

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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The Phosphate Deposits

Of Florida

A Dissertation

Submitted To The Faculty Of The Ogden Graduate School

OF SaENCE IN CANDIDACY FOR THE DEGREE

Of Doctor Of Philosophy

(department of geology)

By

George Charlton Matson

A Private Edition

Distributed By

The University of Chicago Libraries

Reprinted from

United States Geological Survey Bulletin 604

Universiiy Of Michigan Ubraries

XCbe JSLnivcxBltv of Chicago

The Phosphate Deposits

Of Florida

A Dissertation

Submitted To The Faculty Of The Ogden Graduate School

OF SaENCE IN CAKDIDACY FOR THE DEGREE

Of Doctor Of Philosophy

(department of geology)

J[ By

George Charlton Matson

A Private Edition

Distributed By

The University of Chicago Libraries

Reprinted from United States Geological Survey Bulletin 604

DEPAKTMKNT OF THE INTERIOK UNITED STATKS GEOLOGICAL SUltVEY

OEOBQB OTIS SMITH. Dutccron

Bt7ZJ.ErrcN 604

The Phosphate Deposits Of Florida

George Chaklton Matson

Washington

Ooveknment Printing Oppio

Tf/

Contents,

, Page.

Classes and general fonn and features 7

History and production 7

j' Distribution of phosphate deposits 9

General conditions 9

Rock phosphate 9

Land-pebble phosphate 10

River-pebble phosphate 10

Soft phosphate 10

Geology 11

Nomenclature and lithology of the formations 11

Tertiary system 11

Oligocene series 11

Vicksburg group 11

Definition and subdivisiona 11

Lithologic character 12

Distribution 12

Apalachicola group 12

Subdivisions 12

Chattahoochee formation 13

Tampa formation 13

Lithologic character 13

Distribution 13

Alum Bluff formation 13

General features 13

Lithologic character 14

Distribution 16

Miocene series 15

Subdivisions 15

Choctawhatcheo marl 15

Lithologic character 15

Distribution 16

Jacksonville formation 16

Lithologic character 16

Distribution 18

Pliocene series 18

Subdivisions 18

Caloosahatchee marl and Nashua marl 19

Age 19

Lithologic character 19

Distribution , 19

Alachua clay 20

Age 20

Lithologic character 20

Distribution 21

Bone Valley gravel 21

Age 21

Lithologic character 21

Distribution 22

4 Contents.

Geology — Continued. lagp.

Quaternary system 22

Pleistocene series v 22

Subdivisions 22

Lithologic character 22

Distribution 22

Recent series 23

Character and occurrence of the depopits 23

Rock phosphate 24

Form and general features 24

Matrix 25

Flint and limestone 26

Overburden 26

Deformation 27

Size and shape of deposits 28

Thickness 28

Local details of rock-phosphate deposits 29

Newberry district 29

Dunnellon district : 31

Hernando and vicinity 32

Phosphate of Alum Bluff formation (" bedrock'') 33

Phosphate of Bone Valley gravel or land-pobble phosphate 35

Distinctive features 35

Animal remains 36

Quartz and chert 37

Overburden 37

Size and shape of the deposits ' 37

Thickness 38

Local details 38

Northern part of region 38

Mulberry and vicinity 40

Fort Meade and vicinity 42

Phosphatic marl 44

Character and uses 44

Development at Fort Meade 45

River-pebble phosphate 45

Origin and age of the phosphates 45

General conclusions 45

Rock phosphates of the Vicksburg group 46

Theories of origin 46

Types of rock phosphate discriminated 49

Rock phosphate formed in place 49

Redeposited phosphate 52

Source of the phosphoric acid 53

Phosphate of Alum Bluff formation ("bedrock ") 58

Marine phosphatic nodules 58

Source of the phosphoric acid 63

Phosphate of Bone Valley gravel (land -pebble phosphate) 65

River-pebble phosphate 67

Topographic position 67

Source of phosphate 67

Rock phosphate 68

Phosphates of Apalachicola group 68

Bone Valley gravel (land -pebble phosphate) , 69

River-pebble phosphate 69

Contexts. 5

Page.

Composition of the phosphates 69

Commercial requirements 69

Rock phosphate 70

Waste from rock phosphate 75

Phosphates of the Alum Bluff formation 77

Land-pebble phosphate 79

Waste from land-pebble phosphate 82

Phosphatic marl 83

River-pebble phosphate 83

Mineralogy 84

Phosphate mining 89

Classes of phosphates mined 89

Rock phosphate 90

Stripping 90

Excavating 90

Raising and washing 91

Sorting 91

Drying 92

Waste products. 92

Pebble phosphate 92

Stripping 92

Excavating '. 93

Washing 93

Sortmg 94

Drying 94

Waste products 94

Bibliography of Florida phosphates 95

I ndex 99

Illustrations.

Page.

Plate I. Map showing geology of the peuinRular portion of Florida In pocket.

II. General view of rock-phosphate mine 8

III. Map showing the phosphate deposits of Florida 10

IV. A, Bowlders of rock phosphate embedded in a matrix of clay and

soft phosphate, Newberry region; By Fragment of a bowlder of rock phosphate showing cavities lined with crystalline phosphate

minerals and containing phosphatic stalactites 24

V. Fragment of a bowlder of rock phosphate showing part of a cavity'-

lined with crystalline phosphate minerals 25

VI. Ay Fragment of rock phosphate composed of plates; By Broken plates

of rock phosphate cemented by phosphate 26

VII. Ay Phosphate deposit containing bowlders of flint and pillars of lime- stone, the whole covered by Pleistocene sands; JB, Stratified Pleis- tocene sands resting unconformably on phosphate and semi- indurated sands that have been broken and distorted 27

VIII. Ay Phosphatized limestone belonging to the Alum Bluff formation

("bedrock") ; By Coarse semi-indurated pebble phosphate 34

IX. Part of the jawbone of a mastodon 36

X. Specimen shown in Plate IX, viewed from above 37

XI. A, Part of the tusk of a mastodon; 5, Tooth of a mastodon 38

XII. Jawbone and teeth of animals: A and By Jawbone of a manatee; Cand.

D, Two views of the tooth of a horse ; Ey Tooth of a rhinoceros 39

XIII. A, Relations of rock phosphate to underlying limestone in Cummer

Lumber Co. 's mine at Newberry; By General view of Cununer Lum- ber Co. 's mine at Newberry 50

XIV. Ay Plate-rock phosphate near Anthony; By Phosphatized limestone of

Vicksburg group 51

XV. Fragment of phosphate containing cavities coated with deposits of

crystalline phosphate and partly filled with phosphatic stalac tites. 52 XVI. Ay Contact of Alum Bluff formation (" bedrock ") and overlying Bone Valley gravel ; By Undulating layers of pebble phosphate of varying

texture, containing fragments of bones 66

XVII. General view of pit in the rock-phosphate region, showing mining by

dredging 90

Figure 1. Diagram showing relations of Peninsular" limestone to sandstone,

rock phosphate, and gray Pleistocene sand 52

2. Diagram showing relations of "Peninsular" limestone to eandstone,

rock phosphate, and gray Pleistocene sand 53

The Phosphate Deposits Of Florida.

By George Charlton Matson.

Classes And General Form And Features.

The phosphates of Florida are of three distinct types — rock phos- phate, pebble phosphate, and soft phosphate. The rock phosphate consists of bowlders and pebbles, of many sizes and shapes, embedded in a mass of sand, clay, and soft phosphate, the whole being usually intermingled in varying proportions. In a few deposits the coarse and fine fragments of phosphate are more or less definitely separated, the large pieces, comprising cobbles and bowlders, being aggregated near the bottom, but even where there is a general separation the larger pieces are likely to be scattered sporadically through the whole deposit, and fine materials may be found in any part of a bed. The rock phosphate ranges in color from light gray or white, the usual colors, to yellow, brown, or dark blue.

The pebble phosphates are composed of rounded or subangular pebbles embedded in a matrix of sand, clay, or soft phosphate. The materials show more or less assortment into alternating layers of coarse and fine pebbles in a matrix which is in most places sandy, but in some deposits consists of fine clay or soft phosphate. The color of the pebbles ranges from light gray to blue or black.

The soft phosphate is in fine powder or in soft masses that crumble to dust when dry but are very plastic when wet. Phosphate of this type is commonly white, though it may be colored yellow or brown by ferric hydroxide or other substances. Soft phosphate foims a large portion of the matrix enveloping the fragments of rock in the rock-phosphate deposits. A part of the matrix in many deposits of pebble phosphate consists of soft phosphate, but the percentage of sand and clay in such deposits is usually larger than in those of rock phosphate. Some deposits in regions underlain by limestones contain few pebbles of rock phosphate, but such deposits are small.

History And Production.

Phosphate has been mined in Florida since 1888, and for many years the State has been an important source of phosphate for the manufacture of high-grade fertilizer, which has been made and used both in this country and abroad. Mines have recently been opened

Phosphate Deposits Of Florida.

on some of the ocean islands, but notwithstanding this fact the exploitation of Florida phosphate has continued with only temporary fluctuations, which were probably due largely to fluctuations in the demand. During 1909 some of the mines reduced their output and others suspended work, but early in 1910 many mines were reopened and nearly all the large mining companies began prospecting to discover new deposits of liigh-grade rock. By the summer of 1911 the number of active mines had increased, and during that year more phosphate was mined in Florida than in any preceding year.

River-pebble phosphate was mined as early as 1888 on Peace Eiver near Arcadia, the principal mines being along the river, though some mining was done along other streams. The amount of rock produced annually reached a maximum of nearly 125,000 tons in 1893 and then declined until operations were suspended in 1908.

The exploitation of rock and land-pebble phosphate deposits began about 1889 or 1890. During the earlier years of the industry in Florida the quantity of land-pebble phosphate mined was rather small, the mines being nearly all on low-grade deposits, some of them con- taining less than 70 per cent tricalcium phosphate, but in recent years the discovery of high-grade land-pebble phosphate containing 75 to 80 per cent tricalcium phosphate has led to a considerable increase in the amount of rock mined. There has also been a marked increase in the demand for the lower grade rock, so that the produc- tion in 1910 was more than a million and a half tons.

The rock phosphate was formerly guaranteed to contain not less than 75 per cent tricalcium phosphate and not more than 5 per cent of iron oxide and alumina. The demand for rock of this grade was large enough to cause the opening of a number of mines to furnish phosphate for exportation, but later the minimum standard was raised from 75 to 77 per cent tricalcium phosphate, and the maxi- mum of iron and alumina was fixed at 3 instead of 5 per cent. This change led to the abandonment of some mines but stimulated the working of high-grade deposits (See PL II) until the output is now more than two and a half million tons annually.

The quantity of phosphate rock marketed in Florida during the years 1909-1913 is shown in the table below:

Phosphate rock marketed in Fhrida, 1909-1913, classified by grades in long tons.

Year.

Hard rock.

Land pebble.

River pebble.

Total.

Quantity. Value.

Quantity.

Value.

$4,614,968 5,595,947 6,712,189 6,168,129 6.575,810

Quantity.

Value.

Quantity.

Value.

513, 5S5 W, 026, 333 438,347 3,051, S27 443,511 2,761,449 491,481 3,2a3,l<J8 489,794 1 2,987.274

1,266,117

1,629,1<10

a 1,992, 737

a 1,913,418

2,065,482

1,779,702 2,067,507 2,436,248 2,406,899 2,546,276

$8,541,301

8,647,774 9,473,638

1910. .. .

(6)

(ft)

(6)

9,461,297

9,563,084

o Includes a small quantity of river pebble.

b Included in land pebble.

Phosphate Deposits Op Florida. 9

Distribution Of Phosphate Deposits.

General conditions. — SmaD deposits of phosphate and phosphatic rock occur at many places in Florida; in fact, phosphate appears to be very widely distributed in the northern and central parts of the peninsula, and deposits are found on the west side of Apalachicola River in western Florida. (See PL III.) The areas of workable phosphate, however, are confined to certain parts of the peninsula, and even in areas that are usually included in the phosphate region only a very small percentage of the land actually contains enough phosphate to warrant exploitation.

RocJc phosphate, — Deposits of rock phosphate occur on Wacissa, Aucilla, Fenholloway, and Suwannee rivers, in Jefferson and Taylor counties, and though none of these deposits are now mined, some of them might be exploited if better facilities for transportation were provided. Near Luraville there are rich deposits of rock phosphate, but attempts to mine them have been abandoned because the per- centage of iron oxide and alumina in the phosphate exceeds the present limit prescribed by the purchasers. In these deposits the alumina is in the interior of the pebbles and bowlders and conse- quently is not readily removed by washing. The rock-phosphate region, where mining has been most active, forms a narrow belt beginning in southeastern Suwannee and southern Columbia counties and extending southeastward to High Springs, where it bends south- ward across western Alachua and Marion and eastern Citrus and Hernando counties.

Many active mines are located along Barr's tramroad, a few miles west of the Atlantic Coast Line Railroad, extending from a point near Clark southward beyond Newberry. The number of mines decreases southward toward Archer, and mining has been discon- tinued at Albion, in Levy County. The Early Bird and Eagle mines were long ago abandoned, but two mines are in operation near Stand- ard and one near Juliette, in western Marion County. Dunnellon, in southwestern Marion County, is an important center of rock-phos- phate mining, several mines being located near that place on terraces bordering Withlacoochee River and others on a terrace bordering the west side of Tsala Apopka Lake. There is a rock-phosphate mine a few miles west of Istaohatta, in northeastern Hernando County, and another just south of Croom, in the east-central part of the same county. The rock-phosphate deposits extend into western Sumter County and southward a few miles beyond Richland, in eastern Pasco County, but the rock in Sumter and Pasco counties is of low grade and is not being mined.

Phosphate that has generally been classed as plate rock is found in central Marion County. Several mines were opened in the plate-

10 Phosphate Deposits Op Florida.

rock region along the Seaboard Air Line Railway, northeast of Ocala, but all have been closed for some time. The best deposits of this rock are near Sparr and Anthony and 5 or 6 miles east of Ocala. Bowlders of phosphate were at one time mined near Welshton, but operations were suspended many years ago, when the introduc- tion of log washers made it possible to mine finer material, and no mines are now being operated in the plate-rock region.

Land-pebble phosphate. — The extent of the land-pebble phosphate (Bone Valley gravel) is discussed in the geologic r6sum6, on page 22. The principal centers of mining are at Mulberry and Fort Meade, but mines are located as far north as Plant City and Medulla, and it is rumored that one is soon to be opened between MeduUa and Winston. Mulberry is an important center for pebble-phosphate mining and there are a number of mines along the Atlantic Coast Line Railroad between Mulberry and Fort Meade. South of Fort Meade there are mines at Jane Jay and near Bowling Green. Some prospecting has been done near Turkey Creek, and mines will probably be opened farther west than those now in operation. There are also rumors of impending development southeast of Fort Meade.

River-pehhle phosphate. — River-pebble phosphate was formerly mined along Peace River from Mulberry southward. Arcadia was at one time the principal center for the exploitation of this kind of phosphate rock, but in recent years there has been considerable mining near Fort Ogden and Hull. Pebble rock was also mined on Alafia River and on Black Creek, a tributary of St. Johns River. Since 1908 no river-pebble phosphate has been mined in Florida. In addition to the localities already mentioned, pebble phosphate has been reported on Manatee, Miakka, Kissimmee, and Caloosahatchee rivers and at the mouth of Fisheating Creek, but none of these streams is known to afford workable deposits.

Pebble phosphates were collected by Eldridge in T. 1 N., R. 12 E., and T. 2 N., Rs. 13 and 14 E., all of the meridian of Tallahassee. Speci- mens of similar character were obtained aLso from T. 1 S., R. 14 E. of the Tallahassee meridian. It is not certain that these deposits are of the river-pebble type, but in any event there is evidence of the presence of rock phosphate in that part of the State, and the pebble phosphate has probably been derived from the rock phosphate by erosion and redeposition either by streams or by wave action during a period of submergence.

Soft phosphate. — Soft phosphate forms a variable proportion of the matrix that surroimds the fragments of rock phosphate in aU the deposits of the hard-rock type. It also incloses pebbles of phosphate in the land-pebble region, but it is less important there because the deposits are prevailingly coarse and much of the matrix is sandy. In addition to its occurrence with the other types soft phosphate occurs

U. a. QEOLC

zrf

z4

Geology. 1 1

in small; more or less isolated pockets in the limestones of the Vicks- bm'g group, and in larger areas, scattered over several square miles, south of Greer and northwest of Ocala. Soft phosphate is found also southwest of Richland, in Pasco County. There is practically no demand for this kind of phosphate, though it should be a valuable fertilizer for use on soils of certain types.

Geology.

Kohekclatube And Lithoix>Gy Of The Formations.

The geology and topography of Florida have been discussed by many writers, and the detailed consideration of these subjects may therefore be omitted from this report. It is necessary to give a brief summary of the geology of the northern part of the peninsula, how- ever, in order to furnish a basis for the discussion of the mode of occur- rence, geologic relations, and origin of the phosphates. A comprehen- sive summary of the geology is given in a table published in the Second Annual Report of the Florida Geological Survey,* which is here reproduced (opp. p. 12) after revision to conform to the present state of knowledge of the geology of Florida. The deposits called the Hawthorn formation have for a long time been known to be the equivalent of a part of the Alum Bluff formation, and the deposits heretofore described under that name are in this report included in the Alum Bluff formation. The evidence for the abandonment of the name "Hawthorn formation'' has recently been briefly discussed by Messrs. Vaughan and Cooke, and will be fuUy presented in a detailed report to be pubUshed later.

The map accompanying this report is in part a reprint of one prepared for a report on the geology and groimd waters of Florida,* but it has been revised and corrected by means of studies made sub- sequent to the publication of the earlier report. The map is con- structed with special reference to the Tertiary geology, for the com- mercial deposits of phosphate are associated with rocks of Tertiary age.

Tebtiaby System.

OLIGOCENE SERIES. VICKSBTmO OKOTHP.

Definition and subdivisions, — The oldest rocks known in Florida belong to the Oligocene system, and the oldest Oligocene rocks belong to the Vicksburg group, which comprises a large part of what was

I Matson, Q. C, and Clapp, F. O., A preliminary report on the geology of Florida, with special reference to the stratigraphy: Florida Geol. Survey Second Ann. Kept., 1909.

s Vaughan, T. W., and Cooke, C. W., Correlation of the Hawthorn formation: Washington Acad. Sci. Jour., voL 4, No. 10, pp. 250-253, 1914.

Matson, O. C, and Sanford, Samuel, Geology and ground waters of Florida: U. S. Oeol. Survey Water-Supply Paper 319. 1913.

12 Phosphate Deposits Of Fi-Orida.

once called the Vicksburg limestone. However, some of the deposits that were formerly included in the Vicksbm'g have for several years been classed with post-Vicksbm'g formations. The Vicksburg group in Florida has been divided into three formations, known as the Marianna limestone, the "Peninsular'' hmestone, and the Ocala limestone. These three formations are similar in hthologio character and will therefore be discussed here as a single group. These lime- stones are of especial interest because they underlie all the rock phosphate now mined in Florida.

Lithologic character. — The Vicksburg group includes white or light- colored porous limestones, which are generally soft and crumble so easily that it is diflScult to obtain good specimens. On exposure to the air, however, the surface of the limestone hardens as a result of the deposition of calcium carbonate in the outer pores of the rock. Samples obtained in drilling deep weUs show that these rocks are remarkably uniform in color and texture to a depth of several hundred feet beneath the surface in the peninsula of Florida. However, the upper part of the limestones of the peninsula include a slight admix- ture of land-derived sediments, such as clay and fine sand, and well records indicate that similar conditions exist in western Florida. Layers of Ught-blue or gray chert, ranging in thickness from a fraction of an inch to several feet, occur in the hmestones of this group. Irregular masses and bowlders of flint are found at many places where the rocks belonging to this group are at the surface, and the shells embedded in this flint serve as a valuable guide to determine the areal extent of the rocks of Vicksburg ago.

Distribution, — The limestones of the Vicksburg group underlie all of Florida, but except in small areas in the peninsula and in western Florida they are covered by younger beds of sand, clay, or limestone. In the peninsula the principal area in which these limestones lie at or naar the surface extends from a point near Sutherland, HiUsboro County, and Dado City, Pasco County, northward nearly to Fort White and Lake City Junction, Columbia County. The best expo- sm*es are in Pasco, Sumter, Lake, Citrus, Hernando, Marion, Levy, Lafayette, Alachua, Suwannee, and Columbia counties. Near the margin of the area of the Vicksburg (see map, PL I, in pocket) there are many more or less isolated exposures, the best known being the outliers in Taylor, Jefferson, Columbia, and Suwannee counties.

Apauichicola Oroitp.

Subdivisions.

The Apalachicola group (see table opposite) is now divided into three formations — the Tampa, Chattahoochee, and Alum Bluff — the Chattahoochee and Tampa formations being probably in part

Reoent.

Plebtooene.

PUooene.

Miocene,

Ap

OUgDoeme.

85816*— Bui

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f

r f

t

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tl

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G TV su m ar ou

thi

Geology. 13

contemporaneous and the Alum Bluff formation being younger. The deposits heretofore described imder the name '' Hawthorn for- mation" have been found to be the same as the Alum Bluff forma- tion, and they are therefore here included in that formation, as explained on page 11.

Chattahoochee Formation.

The Chattahoochee formation consists of Ught-colored limestones and marls and lies mostly in western Florida. It rests upon an eroded surface of the Vicksburg group and occupies the northern part of the area of the Apalachicola group as it is outhncd on the map (PL I, in pocket).

Tampa Formation.

Lithologic character. — Like the Alum Bluff formation, the Tampa formation contains both limestone and elastic materials. At the base of the formation at the type locaUty near Tampa is a tough blue clay, over 40 feet thick, containing more or less sand, probably in the form of thin laminae. Above the clay is a hmestone having a thickness of over 25 feet and containing a sihcified layer ranging in thickness from a few inches to over 10 feet. This layer of silicified limestone is very fossiliferous and has been called the Orthaulax zone because it contains a certain shell belonging to that genus. Some clays that overlie the upper limestone of the Tampa formation were formerly included in it, but recent investigations have shown that they belong to the Alum Bluff formation.

Distribution. — The Tampa formation is exposed along the shores of old Tampa Bay and Ues beneath the smf ace of the peninsula west of the bay. The limestones of this formation probably extend north- eastward into Pasco and Polk counties, and the formation has been recognized as far south as Manatee River, on the west coast. Its occurrence in the interior of the peninsula has not yet been deter- mined, but it probably extends some distance up the north prong of Hillsboro River.

Alum Bluff Formation.

General features. — The Alum Bluff formation is one of the most interesting and widespread formations in Florida. It includes a great variety of sediments, ranging from pure, fine-grained clays to sands, marls, and limestones. It is of considerable economic im- portance because it supphes all the fuller's earth and a httle of the phosphate now being mined in the State. As explained on page 11, it includes the deposits heretofore described under the name Haw- thorn formation, recent work having proved that those deposits are the same as the typical Alum Bluff formation.

14 Phosphate Deposits Of Florida.

LUhologic character. — The most, prominent constituent of this for- mation, especially where it is at the surface, is a coarse gray sand, which, where thick, is covered by a growth of stxmted timber known as "scrub." The "big scrub" that lies east of Oklawaha River is a good example of the stunted vegetation found in some places on the sands of the Alum Bluff formation. Shell marls (sand containing shells) are common at certain geologic horizons, especially near the top of the formation in the western part of the State. Clays are locally abundant, among them being deposits of fuller's earth. These deposits are now being mined in the vicinity of Quincy and near EUenton, on Manatee River, but similar deposits are foimd in other parts of the State, especially in Gadsden Coimty. Limestones are not numerous in the Alum Bluff formation, but thin beds occur in the upper portion. These limestones are shallow-water deposits, generally more or less earthy, containing shells of marine animals that inhabit shoal water. The Florida Geological Survey recog- nizes three members of this formation — the Chipola marl, the Oak Grove sand, and the Shoal River marl. The " Sopchoppy limestone"' was also tentatively included in the Alum Bluff formation and the propriety of including it is shown by the fact that for this report a basis of correlation was found in the collections of fossils obtained from a Ught-gray to yellow phosphatic limestone that underhes the pebble phosphate and is known locally as "bedrock." In connection with the discussion of the phosphate deposits a more detailed descrip- tion of this "bedrock" will be given. Its faimal relations to the Oak Grove sand member indicate that it belongs to the upper part of the Alum Bluff formation, and its similar relation to the "Sop- choppy limestone" strengthens the belief that the limestone Ues at about the same geologic horizon as the Oak Grove sand. The collections made from the limestones of the Alum Bluff formation represent several localities, but the largest number of well-preserved specimens came from the pit of the Coronet Phosphate Co., about 5 miles southeast of Plant City. W. H. Dall selected some of these specimens for examination and in a letter to the author gave the results of his studies as follows :

I have made a very careful and particular examination of the most characteristic fossils I could find in the material from 5 miles southeast of Plant City, Fla., with the following results:

Busycon n. sp.

Pecten sayanus Dall (Oak Grove up).

Pecten (almost certainly) poulsoni Morton.

Area eantarosana Dall (Chipola, Sopchoppy," Oak Grove).

Area (probably) dodona Dall (Oak Grove).

1 Matson, O. C.,and Clapp, F. G., A preliminary report on the geology of Florida, with special reference to the stratigraphy: Florida Geol. Survey Second Ann. Rept., pp. 102-106, 1909. s Idem, p. 103.

Geology. 15

Area umbonata Lamaik (Chjpola to Recent).

Chione glyptocyma Dall (Oak Grove).

Cardita tegea Dall (Chipola, "silex beds'*).

Mytiloconcha incurva Conrad (lower Miocene of New Jeraey and Maryland, " iSop- choppy limestone " ) .

I have added the distribution, which shows that the horizon is upper Oligocene, probably near the Oak Grove, Santa Rosa Cotinty, Fla., horizon. It is a "beach" deposit, as shown by the way in which the shells are tumbled together and by the presence of shore barnacles. The Pecten (?P. pouhoni) is a fragment and may be rmani. I think the species is not known to have survived the era of the "Penin- sular" limestone.

lu the pebble-phosphate region the limestones of the Alum Bluff formation contain numerous pebbles of phosphate and some clay and sand and are interbedded with layers of clay containing pebbles.

IHstribyiion. — The Alum Bluff formation lies near the surface over a large part of the north end of the State, whence it extends south- ward in a belt between Oklawaha and St. Johns rivers. It extends across Central Lake County, but near the headwaters of Withlacoo- chee and Eassimmee rivers its distribution has not been determined. From the vicinity of Haines City it extends southwestward, passing beneath the younger formations. The sandy phase of this formation may be represented in a ridge bordering the west side of Kissimmee Valley, somewhat farther south than the latitude of Fort Meade. This part of the State has not been examined carefully, but descrip- tions furnished by casual visitors and residents suggest the occur- .rence here of sands of the Alum Bluff formation.

Miocene Series. Subdivisions.

Two formations of Miocene age, known as the Choctawhatchee marl and the Jacksonville formation, have been recognized in Florida, and it is possible that the Bpne Valley gravel and the Alachua clay, after eliminating the "Peace Creek bone bed," may also be Miocene,

Choctawhatchee Marl.

Lithologic character. — The Choctawhatchee marl consists of gray to green or blue sands and shell marls and, in some localities, of clays. The sands are moderately coarse and in many places contain fine glis- tening scales of mica. Locally they show a slight tendency to indu- ration because of the presence of a small amount of calcium carbonate, which acts as a cement, binding the sand grains together. Intermin- gled with the sands there is usually a little dark-colored earthy matter, and the presence of iron compounds is indicated by the red and yellow stains that appear where the surface of the sands has been exposed to the weather.

16 Phosphate Deposits Of Florida.

Some layers contain a large numbGr of shells of marine animals such as lived in shaflow water during the deposition of the beds of Miocene age. In many places these shells are almost perfectly preserved, but the occurrence of broken and worn fragments indicate that some of the animal remains were subjected to more or less dis- turbance by the waves of the Miocene sea. At a few places a deposit of clay has been observed in the upper part of the formation.

Distribution, — The distribution of the Choctawhatchee marl has been indicated on the map, but owing to poor exposures the details of the occurrence of this and other formations are not known. The principal area of this marl stretches from a point near the northwest corner of Florida eastward nearly to Tallahassee. The exposures occupy a narrow belt and the formation dips seaward beneath the younger deposits that fringe the Gulf coast. Small patches of marl similar to that already described are found in the St. Johns Valley and as far west as Brooker, giving additional evidence of the possi- biUty of the existence of a Miocene strait across the northern end of the peninsula. Similar marl has been observed in drillings from thi wells at Kissimmee and it doubtless underUes the southern end of the peninsula.

Jacksonville Formation.

Litlwlogic character. — The Jacksonville formation consists of a thick deposit of interbedded sand, sandstones, and clays, with some layers of limestone near the top. No good exposures of the sands and clays have been observed, but the character of these deposits is shown by samples obtained in drilhng a well at Jacksonville. The log of thk well, supplied by Mr. II. N. Ellis, follows:

Log of well at Jacksonville Fla.

Feet.

Filled ground and sand - 15

Varicolored gray to red sand 15 - 34

Gravel 34 - 34 J

Yellowish fosailiferous rook 34J- 40

Gravel with water 40 - 44

Gray fosailiferous rock 44 - 53

Clay, with thin layers of whito rock 53-58

Blue clay, with black gravel at 68-70 and 82-89 feet 58-89

Rock 89 - 94

Blue clay and black gravel 94 -100

Rock, 2 inches thick 100

Blue clay with quartz sand and very fine black gravel 100 -130

Very hard compact clay and sand 130 -142

Greenish sandy clay 142 -204

Greenish sandy clay with more or lees black gravel and oc- casional streaks of pure clay 204 -250

Sticky clay and sand and fine gravel 250 -263

Rock 263 -263i

Greenish sandy clay and heavy gravel bed 263 J-272

of

Jy

Geology. 17

Blue clay containing very fine sand 272 -287

Sand rock 287 -289

Bed of shells, oysters, etc., living types 289 -290

.t White clay 290 -294

is- Sand with clay enough to hold it 294 -298

Compact greenish sandy clay with streaks of nearly pure clay . 298 -314

Sand containing shells; just enough clay to hold them 314 -320

Shells with scraps of fossil bone T 320 -330

"Coquina" rock 330 -331

l3 Clay 331 -340

e Blue clay and sand 340 -350

Sticky blue clay; very little sand 350 -358

Clay with black gravel 358 -365

Blue clay with gravel and shell casts 365 -368

White clay with gravel 368 -375

I White marl with very little sand 375 -385

Light-colored clay 385 -390

Greenish clay 390 -400

Greenish sandy clay 400 -410

Sticky clay 410 -428

Clay with very little sand 428 -434

Nearly pure clay; very light when dry T. . . . 434 -443

Bluish sandy clay with gravel and streaks of sticky clay with

some nodules of rock 443 -470

Rock 470 -470i

Greenish clay with fine sand above and coarse sand below;

small flow of water at 487 feet 470i-487

Rock bowlder (siliceous concretion) in blue sandy clay 487 -492

Compact blue clay 492 -496

White clay 496 -497

Conglomerate rock 497 -499

Hard browniali rock 499 -504

Very hard compact rock (siliceous ILmostoiu;) 504 -510

Soft white rock with some water 510 -519

Hard compact rock 519 -524

Very soft white rock in layers 1 to 5 feet thick, with strata of more compact rock 3 to 12 inches thick; increase in the flow of water on breaking each hard stratum. Gaged flow at 632

feet 1,000,000 gallons in 24 hours 524 -727

Compact brown rock; no water 727 -758

Alternate hard and soft strata of grayish rock with very little

water 758 -865

Soft white rock with hard brown layers 1 to 3 feet thick every

few feet; a slight increase of flow from each soft layer 865 -930

Very hard brown rock 930 -935

Soft brownish rock with hard layers, flow increasing as each

hard layer is broken 935 -950

Alternate layers of hard and soft rock; small increase in flow. . 950 -970 More compact rock; no water 970 -980

The sands and gravels from the surface *to 34J feet are probably Pleistocene, though they may include some Pliocene beds.

85816— Bull. 604—15 2

18 Phosphate Deposits Of Florida.

The fossiliferous limestone encountered at 35 feet belongs to the Jacksonville formation, which is thought to extend to a depth of at least 496 feet, though it is possible that this measurement may include some sands and clays of the Alum Bluff formation.

The limestones of the Jacksonville formation range in color from white or light gray where they are fresh to pale yellow or yellowish- gray where they have been exposed to the weather. When examined with an ordinary hand lens the limestone is seen to bo prevailingly coarse grained and to contain a largo proportion of sand and a more careful examination shows the presence of considerable clay. Some layers of this rock are abundantly fossiliferous, but the animal remains consist of casts and molds left after the original shell had been removed by solution.

Distribution. — The distribution of the Jacksonville formation is imperfectly known, but similar rock is exposed near Zellwood, in Orange County, and the artesian wells at St. Augustine pass through sands and clays that resemble those at Jacksonville. Possibly the deposits of Miocene age encountered in the deep well at Palm Beach should be referred to this formation. The Jacksonville formation is known as far west as Waldo, and either it or the Choctawhatchee marl may extend entirely across the north end of the peninsula, as Miocene fossils have been reported from the valley of Suwannee River.

Pliocene Series. Subdivision 8.

The Pliocene deposits of Florida have heretofore been divided into five formations — the Caloosahatchee and Nashua marls, the Alachua clay, the Bone Valley gravel, and the Lafayette formation. Here- tofore the first four of these formations have been regarded as largely contemporaneous. Recent work, however, has shown that the Ala- chua clay and Bone Valley gravel are perhaps older and that they may be even of Miocene age, but until conclusive evidence of their age has been discovered they are for the present' retained in the Pliocene.

In the report on the geology and ground waters of Florida,* atten- tion was called to the fact that the materials included in the assem- blage called the Lafayette formation in Florida did not comprise a distinct formation, but are in part upper OUgocene, in part Miocene, and in part Pliocene.

The collection of vertebrate fossils obtained from the rock-phos- phate mines along Withlacoochee River in the vicinity of Duimollon

1 Mataon, O. C, and Sanford, Samuel, Geology and ground waters of Florida: U. S. Geol. Survey Water-Supply Paper 319, p. 147, 1913.

Geology. 19

was submitted to J. W. Gidloy, of the United States National Museum, and his report on these specimens follows:

The vertebrates from the Dunnellon, Fla., localities, which include one and possi- bly two species of mastodon and a tooth of Elephas primigenitLS (f), represent a con- siderably later phase than the beds at Mulbeiry, being probably nearly the equivalent of the "Loup River beds" (upper Pliocene or lower Pleistocene) of Nebraska.

It is intended in the near future to give these collections a more detailed study, when a complete list of the species represented will be given.

Caloosahatcuee Marl And Nashua Marl.

Age, — The Caioosahatchee marl and the Nashua marl are litho- logically similar and are probably contemporaneous, hence they are here discussed together. Neither of them includes any conmier- cially important deposits of phosphate, though pebbles of phosphate have been reported from the Caioosahatchee marl on Caioosahatchee River. It is not probable, however, that these pebbles are suflSciently numerous to have any economic value.

Lithologic character. — The Caioosahatchee and Nashua marls con- sist of light-gray and blue sandy shell marls interbedded with more or less sand. The shells in these formations, many of which are beautifully preserved, are generally embedded in a matrix consisting of sand and fragments of shoUs. The only diiforence between the two formations is the presence in the Nashua marl of some shells not found in the Caioosahatchee.

Distribution. — Tho known exposures of the Nashua marl are in the vicinity of St. Johns River, between Palatka and Sanford, but the formation is no doubt much more widely distributed and addi- tional field work may disclose many other exposures. The Caioo- sahatchee marl is best known on Caioosahatchee River but is also exposed on the other streams that enter Charlotte Harbor. The best exposures are along Peace River and its tributaries, but other exposures may occur along Miakka River, Prairie Creek, and some smaller streams. The marl probably forms a nearly continuous deposit between these isolated exposures, and the presence of Plio- cene shells in some of the samples obtained from deep wells atKis- simmee suggests that Pliocene marl stretches entirely around the eastern side of the exposures of older formations. It is doubtful whether this can be confirmed by direct observation, because heavy deposits of younger sands obscure the Pliocene beds in the south- central part of the peninsula.

The deposits of Peace Creek and the fossils obtained from Ocala (see p. 20) may bo Plioccno or even Pleistocene, but Uttle is known concerning the relations of the Peace Creek bone bed." It may be either the Pleistocene or Recent deposits formerly mined for river-

20 Phosphate Deposits Of Florida.

pebble phoaphate, or it may be an older deposit exposed by erosion of the stream.

The vertebrate fossils from Ocala were obtained from the over- burden at the pits of the Ocala Lime Co. The bones were embedded in the sand and clay which at that locality overlies the Vicksburg group and extends into depressions in its surface. Their mode of occurrence indicates that these bones may represent parts of the skeletons of animals that were mired in local marshes or lakes, and this and their situation near the level of the uppermost Pleistocene terrace suggest that they may be of early Pleistocene age.

Alachua Clay.

Age. — The reason for believing that the Bone Valley gravel may be Miocene has already been given. The age of the Alachua clay is also in doubt because the fossils may be either late Miocene or early Pliocene. The occurrence of those clays in the interior of the penin- sula, remote from exposures of known PUocene and at altitudes high enough to correspond better with the Miocene, is in favor of their inclusion in the Miocene. Concerning the vertebrate fossils from the Alachua clay, J. W. Gidley, who has recently studied the lists already published, makes the following report:

The faunae of the beds at Archer and Ocala indicate strata at two distinct horizons, the later being much newer than the earlier. With the possible exception of Elephas Columbia from Ocala and Peace Creek, none of the beds in Florida contain ny species in conmion with beds of the Western Plains region, hence an accurate estimate regard- ing the age of these beds relative to those of the West is not yet possible.

The presence of Elephas and true Equus, as well as specimens referred to Bison, CervuB, and Megalonyx, in the deposits of Ocala and Peace Creek suggest a Pleistocene age for these beds, although they may just as well be late Pliocene. Judging from the less advanced stage of development of the species, these beds seem to be older than the deposits at Hay Springs, Nebr., which have been considered as representing nearly the beginning of the Pleistxxiene, and may be about the equivalent of the Loup River, Nebr., deposits, which are held to be either late Pliocene or early Pleistocene.

The beds at Archer and those at Mixon's contain a fauna which in point of develoj)- ment seems to correspond closely with that of the "Republican River formation" of Kansas and Nebraska, thus bringing them near the dividing line between the Miocene and Pliocene, and they may be, with good reason, placed in either the upper Miocene or lower Pliocene.

The horses are represented by Miocene genera, but the species seem in general to be more highly specialized. This does not necessarily mean a later phase or horizon but suggests it.

From the e\idence furnished by vertebrate fossils, therefore, it may be concluded that the beds at Archer and those at Mixon's, 10 miles east of Archer, are in age near the transition from the Miocene to the Pliocene and that the newer beds at Ocala and Peace Creek, Fla., may be placed in time very near the beginning of the Pleistocene.

Lithohgic character. — The Alachua clay consists of a light-blue sandy clay, weathering to yellow or red on exposure to the atmos- phere. Angular sand is usually a rather large constituent of the

22 Phosphate Deposits Op Florida.

phosphate embedded in clay or sand. The Bone Valley gravel is the formation that furnishes nearly all the land-pebble phosphate, and its age is discussed more fully elsewhere in this report. (See p. 69.)

Distribution. — The extent of the Bone Valley gravel is difficult to determine because the sands are not distinctive and the gravel is exposed at few places except mines and prospect holes. From the vicinity of Plant City and Lakeland this formation stretches south- ward to the latitude of Zolfo Springs, and perhaps even farther, though information concerning its extent in that direction is lacking. Theoretically, the eastern boimdary of tliis formation should be near the west side of the upland that stretches southward from the vicinity of Lakeland, but further study is necessary to determine its eastern limits. Its western boundary has not yet been determined, but it is known to be some distance beyond the mines now being operated.

Qxjateb.Naby System. Pleistocene Series.

SvhdivisionB. — The Pleistocene deposits in Florida have been divided into five distinct formations and a number of deposits, of different lithologic character, that are not designated by specific formation names. In this report the separate discussion of these various subdivisions does not appear to be necessary, as they have little bearing on the occurrence or character of the important deposits of phosphate.

Lithologic character, — The deposits of Pleistocene age consist very largely of sand, most of it moderately coarse, though it contains in some places a admixture of clay, and lenses of fine-grained Pleistocene clay have been encountered in well drilUngs. Shell marls and limestones are common on the lowest Pleistocene terrace, espe- cially in the southern part of the peninsula, but they are not exten- sively developed on either of the upper terraces. Except in the southern part of the State the thickness of the sand does not usually exceed 40 feet.

Distribution, — Attention has already been called to the fact that the Pleistocene sands are in the form of terraces of marine origin. One of these terraces, having an altitude of 20 to 25 feet above sea level, is not important in the phosphate region, but the higher terraces are well developed in certain parts of the rock-phosphate region. In the vicinity of DunneUon a terrace that has been observed in many places extends along Withlacoochee River in a narrow belt having an alti- tude of 40 to 60 feet above sea level. Farther up the river, in the vicinity of Gum Swamp and of Tsala Apopka Lake, this terrace

1 MaUon, G. C, and Clapp, F. O., A preliminary report on the geology of Florida, with special reference to the stratigraphy: Florida Geol. Survey Second Ann. Hept., p. 171, 1909.

Character And Occurrence Of Deposits. 23

becomes much broader, and it is apparently extensively developed in the south-central part of the peninsula. The large prairie just south of Gainesville lies only a little higher than this terrace and was probably formed about the same time, though the basin in which the prairie lies is older than the terrace. Some of the other prairies and lakes, and the broad area that stretches southwestward from Paynes Prairie, probably correspond to the next higher terrace. This terrace extends around the entire peninsula and along the coast of western Florida.

A terrace that rises 70 to 100 feet above sea level extends around the inner border of the terrace just described. Near Dunnellon it is more or less dissected and its surface has been lowered somewhat by the solution of the underlying limestone. In general this terrace is narrower than the one below, but in some places it is several miles wide. In the rock-phosphate region this terrace is extensively developed, its eastern margin stretching across western Marion and Alachua counties and including the important phosphate belt in the vicinity of Newberry. In the area south of Dunnellon nearly all the mines except those that are close to the river are on the surface or on the margins of this terrace. In the southern part of the peninsula also this terrace is extensively tieveloped, but it hes mostly west and south of the pebble-phosphate region and the details of its distribu- tion have not yet been determined. It extends northward across the southern part of the peninsula as far as Center HUl and along the west side of the St. Johns River valley.

The Pleistocene formations of southern Florida have been discussed elsewhere.*

Recent Series.

The deposits classed as Recent include clays, sands, marls, sand rock, and coquina. They resemble similar deposits of Pleistocene age and their differentiation, in many places, is therefore difficult. They are found along the beach in the valleys of the principal streams, in the lake basins, and on the uplands where the wind has built sand hiUs and ridges. There are no recent phosphate deposits except in the valleys of some of the streams that flow across phosphate beds, and the recent accumulations of phosphate are insignificant when compared with those of former periods.

Character And Occurrence Of The Deposits.

There are several different types of phosphate in Florida, but only two of them — rook phosphate and land-pebble phosphate — are commercially important. Practically aU knowledge concerning the

iMatson, O. C, and Sanford, Samuel, Geology and ground waters of Florida: U. S. GeoL Survey Water-Supply Paper 319, 1913.

24 Phosphate Deposits Of Florida.

phosphate deposits has been obtamed by examining mines or by boring prospect holes, and consequently the information available relates to the two types that are now being exploited, which are therefore the deposits here chiefly considered.

B.Oce Phosphate. Form And General Features.

The rock phosphate usually hes beneath a varying thickness of sands and clays and the deposits show great diversity of composition, the commercially valuable phosphate consisting as a rule of pebbles or bowlders, or both, embedded in a matrix of fine material. Large bowlders and small pebbles may be mixed indiscriminately in some parts of a deposit, whereas elsewhere they may occur in different parts of the same section, though more or less segregated. Where there is any marked separation the coarse material usually occurs ne4ir the bottoms of the pits. (See PI. IV, A.) In many of the mines, especially along Withlacoochee River, bowlders predominate, some of them behig so large that they must be blasted before they can be put on the cars and elevated to the washers. Large masses of phosphate rock are by no means uncommon in the upland mines; for example, at the mine south of Croom they are so numerous that a groat deal of blasting is necessary in order to prepare them for handling.

In many of the deposits the pebbles are angular, but in a few they are partly roimdcd. Some are Ught and porous, some hard and dense, and others sliow lamuise that vary shghtly in color and density.

The bowlders are generally rounded or oval, but irregular shapes are not micommon. They may be sohd or hollow, the cavities being lined by minerals that were evidently formed by deposition from solution. The most common lining of these cavities is a fibrous crystalhne phosphate mineral (see Pis. IV, B, and V) of undetermined composition, but in a few cavities calcite, quartz, or other mineials are found. A common structure is a soUd shell surrounding a series of parallel plates, usually less than an inch thick, separated by narrow, discontinuous crevices. (See PI. VI, A.) The lamellae are connected by irregular deposits and many of them show evidence of having been broken and rccemented by phosphate of a slightly different color from the original rock. (See PL VI, B,) The ouU shell of many of tlie bowlders is made up of a dense phosphate showing mon or less distinct bands of different colois.

Plates of phosphate ranging in breadth from a few inches to several feet arc found in many mines. Few of these plat<s are more than a few inches tliick, and, ])ocause of their elasticity, many of them have beoji distorted l)y movements in the phosphate lock. They com-

o (3 t I

Character And Occurrence Of Deposits. 25

monly include more or less clay, which brings the percentage of alumrnnm and iron above the maximum amount permissible, so that it is difficult for the miners to maintain the required standard. In the vicinity of Anthony and Sparr and east of Ocala the deposits contain many plates of phosphate and are known as "plate rock," to distinguish them from the hard-rock deposits foimd elsewhere, but plates of phosphate occur in hard-rock mines in other parts of the rock- phosphate region. (See PI. XIV, A, p. 51.)

Long pendants of phosphate, resemblhrg the stalactites formed in caverns, have been reported in some phosphate deposits. Doubtless their origin was similar to that of limestone stalactites (see PI. IV, J5), and though they are of considerable scicDtific interest they are too rare to have any economic interest or value.

In color rock phosphate ranges from white, gray, or cream to yellow, brown, or black. The pebbles of the upland deposits are usually light colored, ranging from white to Ught yellow or brown, though a few of them are dark brown or even black. Most of the rock mined near Withlacoochee River is dark blue or black, though some Ught- colored pebbles occur in nearly all the river mines. The character of the coloring matter has not been determined, but the color is probably due to both organic and inorganic material, the organic being doubtless more important than the inorganic.

It shoidd not be inferred tliat phosphate is the most abimdant con- stituent of the deposits, for the phosphate is embedded in a fine- grained matrix, and a deposit that will yield 25 per cent of rock of conmiercial value is regarded as very rich. In some mines the pro- portion of phosphate is higher, rising nearly to 50 per cent, but in many others it falls as low as 12 or 15 per cent, and in a part of one deposit the amount of rock obtained was reported to be only about 4 per cent of the whole. Probably not more than 15 per cent of the material mined in the rock-phosphate region is now commercially valuable.

MATRrX.

The phosphate rock is embedded in a matrix composed of varying percentages of clay, soft phosphate, and sand. The proportions of these materials vary in different mines and in different parts of the same mine, but certam generaUzations will apply to the deposits in different parts of the rock-phosphate region. From DunneUon southward clay and soft phosphate predominate in the matrix, which includes only a rather small percentage of sand, whereas in the area north of DunneUon a sandy matrix is most common, though some clay and soft phosphate occur in nearly all the mines. The phosphate is removed from the matrix by washing, and in this process the soft phospluite is carried away with the accompanying sand and day.

26 Phosphate Deposits Of Florida.

This results in the loss of a largo amount of phosphoric acid in the form of soft phosphate, which should be a useful fertihzer for some types of soil.

Flint And Limestone.

Intermingled with the rock phosphate are many pebbles and bowl- ders of flint, ranging in diameter from a fraction of an inch to several feet. In general they have a rounded form, which appears to be original and not the result of mechanical wear. Many of the bowlders are hollow, the interior being lined with quartz crystals; some of them have a more or less lamellar structure, similar to that found in the phosphate; others consist of a core of silicified hmestone containing characteristic fossils of the underlying formation. The outer shells of some of the bowlders are laminated, the laminae being visible because of sUght variations in color; the interiors are usually dark blue, though lighter shades are not uncommon. The flint bowlders and pebbles do not appear to be restricted to any particular part of the phosphate deposit, for they may be aggregated in one place or they may be distributed through the entire deposit. In one mine near Holder a large mass of flint surrounded by phosphate was found near the base of the deposit. It measured 30 feet in length and about 5 feet in diameter. The number of bowlders differs in different mines and in some places they have been so numerous that mining was unprofitable. The phosphate deposits contain scattered pebbles of limestone belonging to the underlying formation. A few of them show progressive alteration from calcium carbonate to calcium phosphate as a result of the action of phosphoric acid upon the limestone.'

Overburden.

The deposits of rock phosphate are everywhere covered by a varying thickness of coarse, angular sand, which is generally light gray or brown in color, is either incoherent or only slightly indurated, and is locally separated from the phosphate rock by a thin deposit of blue or gray clay, which assumes a red or yellow color after exposure to the weather. The sand conceals the underlying materials so effectu- ally that it is seldom possible to discover the phosphate deposits by the surface indications. In a few places phosphatic pebbles lie on the surface, but their presence does not necessarily indicate that there is a valuable deposit underground. It is necessary to bore numerous holes through the mantle of surface sand in order to locate a phosphate deposit and to determine its size and thickness. Borings made for this purpose have shown that the surface sands range in thickness from a few inches to over 50 feet, and, owing to inequalities in the altitude of the surface and irregularities in the phosphate deposits, differences in thickness of several feet may bo found within a radius of a few yards.

F Rock Phosphate Composed Of Plates.

B. Broken Plates Of R

m

in

Character Akd Occurrence Of Deposits. 27

In some mines stratified sands lie above the rock-phosphate deposits and their associated sands and clays. These sands are shown on Plate VII, A and 5, and though they are not everywhere horizontal, the lajers seldom show more than slight undulations, which usually conform to the outlines of the underlying phosphate and its associated materials. They show less induration than the sands associated with the phosphate, and their general freedom from disturbance, together with the fact that the stratification is parallel to the irregular surface of the underlying beds, indicate that they are younger than those beds. The stratification is sufiiciently regular to show that the sands are subaqueous, and their position on a terrace having an altitude of 70 to 100 feet above sea level fixes their age as Pleistocene and serves to correlate them with the uppermost Pleistocene terrace recognized elsewhere in the State.

This terrace has a fairly level surface, its minor irregularities having doubtless been produced by the removal of the underlying limestone by solution since the terrace was formed. The Pleistocene sands are likely to be lighter colored near the surface than the sands at greater depths, the difference in color being due in part to the leaching action of surface waters and in part to mechanical wear where the surface sands have been sUghtly disturbed. Near the surface there is a gen- eral absence of lamination, which is attributed to the fact that the roots of plants have destroyed the original stratification. The tran- sition from the surface sands to those below is locally so abrupt that they were formerly thought to be a distinct formation, but recent investigations show that they belong to the underlying formation.

Deformation.

In most of the rock-phosphate mines portions of the phosphate and associated sands have been considerably disturbed, as is shown by the distortion of layers of phosphatic pebbles and by breaks in the phosphate deposits where the materials have been faulted, one portion having slipped downward. In many places the planes along which the slipping occurred are smoothed and polished, though the amoimt of movement is usually small. The distortion and faulting has locally resulted in enough movement to bring down into the deposits sands and friable sandstones that originally lay above the phosphate. (See PL VII, 5.) This movement has produced sand " horses " in many mines and the sands in many places show evidence of the violence of the movement, their stratification having been destroyed and the material having been reduced to a heterogeneous mass.

The faidting and other disturbances were doubtless caused by the same agencies that produce ordinary sink holes in limestone. The water that percolates into the groxmd carries with it carbonic acid,

28 Phosphate Deposits Of Florida.

derived chiefly from decaying organic matter. This acid enables the water to dissolve the limestone. In the rock-phosphate region the process of solution is rapid, because the underlying limestone of the Vicksburg group is very porous and is readily attacked by the carbonated waters. Solution continues tmiil underground channels or caverns are formed, and after a time it weakens the roofs of these caverns so much that the weight of the overlying rock causes them to collapse, the downfall involving also the superincumbent phosphate and sands. This process is so active in the limestones of the central and western parts of the peninsula that newly formed sink holes axe common, and the present topography has been shaped by solution and consequent collapse of roofs of underground channels. At one point south of Albion the bottom of a phosphate pit that lay above such a cavern is reported to have fallen 4 or 5 feet. Open channels that extend downward to caverns may be seen in some of the phosphate mines near Newberry, and subsidence caused by the broaloBg of cavern roofs may occur at any time, though there is little danger that such a cave-in will occur during the short time a mine is operated.

Size And Shape Of Deposits.

The deposits of rock phosphate differ greatly in size, ranging from single masses containing less than a ton to irregular bodies includmg many thousands of tons. The outlines of the deposits are so irregular that it is frequently necessary to remove inclosed pillars of limestone in order to gain access to small accumulations of phosphate. In many places mining reveals the fact that the phosphate occupies irregular pockets in the limestone and is distributed over areas rang- ing in size from a few square feet to several acres. (See PI. XIII, J., p. 50). Most of the pits in the rock-phosphate region cover only a few acres, but at the Cummer Limiber Co.'s mme, No. 25, near Newberry, a single pit has an aiea of more than 35 acres. Else- where in the Newberry district tlie average size of the phosphaet pits is probably less than 5 acres.

Some large deposits of phosphate are reported to lie near Dunnellon, but none of the pits are as large as the one just described. Deposits covering more than 40 acres have been reported at Dunnellon, and other largo deposits have been found farther south.

TinCKXESS.

The thickness of the rock phosphate varies greatly, reaching a maximum of about 100 feet in the vicinity of Dunnellon and deci cas- ing rapidly toward the northern end of the region and more gradually toward the southern end. Experienced prospectors say that the

Character And Occurrence Of Deposits. 29

maximum thickaess in the vicinity of Newberry is probably not over 50 or 60 feet, and that the average thickness is less than 30 feet. In the area south of Dunnellon the deposits are uniformly muckiticker than they are farther north, and the amount of barren sand overlying the phosphate is geneially greater. Sellards states that the thick- ness of the deposit on the Southern Phosphate Development Co.'s properties neai* Inverness ranges from 50 to 100 feet and averages 70 feet, but these estimates included the thickness of the sand above the phosphate rock.

Local Details Of Rock-Phospilate Deposits.

The individual phosphate deposits are so diverse that it is difficult to present adequate general descriptions that wiU apply to all of them. The sections and descriptions that follow are generalized so far as possible, but the same deposits may present many variations during the progress of mining, so that a section of a deposit as it appears at one stage of mining may be very different from a section of the same deposit after it has been mined for a longer time.

inBWBEBST DISTRICT.

The relation of some of the rock-phosphate deposits to the imder- lying rock is shown at a mine near Newberry. The pit here shows a very uneven surface of limestone of the Vicksburg group, which rises in peaks and ridges 2 to 15 feet high, separated by narrow, irregular channels ranging in width from 10 or 15 feet near the top to 3 or 4 feet near the bottom. Most of these channels in the limestone are not very deep, and from some of them rounded cavities or wells '' (see PI. XIII) containing phosphate extend into the peaks of limestone. The surface of the limestone appears to be smooth, but a soft, porous layer lies at the contact of the Umestone with the phosphate, and this layer in places contains fragments of shells that are characteristic of the limestone.

At one point in the pit is an open cavity that extends downward into the limestone and doubtless reaches an underground channel. The average thickness of the phosphate deposit in this mine does not exceed 15 feet, and it varies from zero where the limestone peaks are near the surface to its maximum thickness in the depressions between the peaks. The overburden is a light-yellow sand having an average tliickness of about 4 feet. The commercially valuable phosphate con- sists largely of small gray pebbles, many of them less than an inch in diameter, and some bowlders, few of them weighing more than 1 ,000 pounds. The largest bowlder reported in this mine made 15 carloads, the car being of the sort used in conveying the phosphate from the

Sellards, E. H., A preliminary paper on the Florida phosphate deposits: Florida Geol. Survey Third Ann. Kept., p. 30, 1910.

30 Phosphate Deposits Of Florida.

pit to the washer and having a capacity of about. tons. This bowlder lay in the upper part of the deposit immediately below the overburden. There is a gradation from soft, friable phosphate near the limestone to denser and harder phosphate in the form of plates, bowlders, and pebbles at some distance from the peaks. In many- places plates of phosphate Ue parallel or roughly parallel to the sur- face of the deposit, but elsewhere they are broken or bent downward, the amount of slumping increasing toward the center of the channels between the peaks of Umestone. At one point a depression in the surface of the phosphate, having a depth of about 20 feet, was filled with sand, which was separated from the adjacent limestone by only about 3 feet of phosphate.

In some places near the limestone the phosphate shows smooth planes (shckensides), caused by slumping of the deposit where the underlying limestone has been partly removed by solution. Most of these surfaces have a very steep inclination which is more or less parallel to the surface of the limestone peaks. (See fig. 2, p. 53.)

Bowlders of fUnt are not numerous in this mine, though a few, more or less rounded, were seen. The deposits contain a few shark teeth and some fragments of bones, apparently parts of the ribs of some animal.

The following section was measured in one of the mines of the New- berry district:

Feet.

Light-yellow sand with dark sandy loam near the top 10-15

PurpUah-brown eand 0-5

Matrix of soft phosphate and clay containing angular pebbles and rounded bowlders of rock phosphate 20

At a depth of 37 feet below the surface a bowlder weighing about a ton was found. It was surrounded by about 4 feet of sand, which was entirely free from phosphate and was inclosed in a matrix con- taining phosphate pebbles. Probably this bowlder and its envelope of sand was carried down into the phosphate by slumping when the supporting limestone was removed by solution. This mine also yielded a mass of flint weighing about 10 tons. Many of the bowlders lie near the top of the phosphate deposit, and some that were observed in this position weighed not less than 3 tons.

Another mine in the Newberry district showed certain features not found in those previously described. At this mine the peaks and ridges of limestone of the Vicksburg group are comparatively rare. The deposit consists of a light-gray matrix of clay and soft phosphate, locally somewhat sandy and containing angular pebbles and rounded bowlders of rock phosphate. The phosphate near the surface is in places stained yellow by a surficial coating of iron oxide. Most of the pebbles and bowlders are light gray, but some are light yellow. A few bowlders have a lamellar structure, and the lamellae are either light

Character And Occurrence Of Deposits. 31

or dark blue. The phosphate exposed above water level is 16 to 20 feet thick, but in places it extends far below water level, and its maximum thickness has not been determined.

There is evidence of subsidence in this pit, for local bodies of sand are found at the same level as the phosphate, their presence being explained by the fact that they have sunk into the pit from above. Wavy and distorted layers occur in the phosphat-o and there are examples of slipping, and many of the planes along which the move- ment occurs show polished surfaces. Above the phosphate and its included bodies of sand is an overburden of light-yeUow sand, which shows horizontal bedding and is clearly younger than the sand and phosphate below. At one point a *'sand horse," in which the layers are considerably broken and stand nearly vertical, is overlain by horizontally bedded sands. The upper part of the overburden con- sists of 2 to 4 feet of lighter-colored sands showing no traces of strati- fication. Here and at many other localities the stratification of the surficial sand has been destroyed by the roots of plants. The contact of the stratified sand in the overburden with the beds below is clearly defined and the layers of the sand are essentially horizontal though they show slight undulations parallel to the surface of the imderlying deposits.

Section of a phosphate mine in the Newberrt/ district.

Foet.

Yellow sand, locally indurated, about 10

Light-yellow and gray soft phosphate and clay matrix containing

pebbles and occasional bowlders of phosphate 15

Yellow clay and soft phosphate containing laige bowlders of phos- phate 10

A few peaks of limestone of Vicksburg age and some bowlders of flint may be seen in the deposit.

DXnrVZLLOK DISTBXCT.

A deposit at one of the mines in the DunneUon district consists of 15 to 20 feet of gray phosphate matrix composed of clay, very fine sand, and soft phosphate containing pebbles and bowlders of gray and yellow phosphate. The pebbles are angular and are of many sizes; some of them exceed 6 inches in diameter, but most of them measure less than an inch. Some bowlders of chert have a diameter of 3 or 4 feet. The overburden consists of 10 to 15 feet Of yellow sand, locally somewhat indurated, and 6 feet of underlying blue clay, weathering yellow.

At a point about 8 feet above the bottom of this pit there are rounded bowlders of fossiliferous rock resembling the "Peninsular" limestone in texture and containing similar fossUs. The shells have been removed by solution, so that nothing but the casts and molds remain, and the entire rock has been altered to a low-grade phosphate

32 Phosphate Deposits Of Florida.

containing no trace of the original carbonate of lime. These bowlders form a layer about 18 inches thick and 4 feet long. The fossiliferous bowlders are coated with soft phosphate, which is partly coherent but crumbles easily. Above the bowlders is a hard, dense plate of phosphate about 2 inches thick, composed of layers of different colors.

It is reported that the phosphate below water level is poorer than that above, faUing on the average below 60 per cent tricalcium phos- phate. The rock below water level also contains more carbonate of lime, alumina, and iron oxide.

The composition of the phosphate that lies entirely below water level can be determined only by examining materials raised by the dredge. One mine of this kind, near Withlacoochee River, stands only a few feet above water level and the rock is obtained by dredg- ing to a depth of over 40 feet. The deposit is prevaihngly coarse and contains many large bowlders. The rock ranges in color from black to gray, but most of it is dark. Many of the fragments of rock that come from the washer are pieces of large bowlders, and some of them consist of a series of parallel plates of dark phosphate rock separated by narrow discontinuous crevices.

The matrix is nearly all clay but in some places includes a little sand. Many of the large bowlders are of very high grade, containing 80 per cent or more of tricalcium phosphate, and a composite sample obtained by mixing small samples from 290 tons analyzed a fraction more than 80 per cent.

This mine has suppUed a great many fragments of bones and some teeth of sharks, mastodons, and elephants. The best informed miners say the bones and teeth of the large animals come from near the edge of the phosphate deposit.

Hebnakbo Ajtd Vicinity.

A typical deposit in this part of tlie rock-phosphate region shows gray phosphate pebbles and bowlders embedded in a soft phosphate and clay matrix. Some of the phosphate bowlders are hollow, others have a lamellar structure, and stiU others are composed of layers of different colors. The phosphate pebbles in this deposit are nearly all angular, but they show some tendency toward stratification, forming layers which are in places bent by unequal subsidence. Associated with the phosphate are a few bowlders of flint 1 to 2 feet in diameter. Most of the flint bowlders are rounded or oval and those that are broken show concentric layers of shades varying from dark to blue. Some of them are hoUow and the cavities are hned with crystals of quartz. Most of the pebbles and bowlders are light yellow to gray, but some are dark. Other bowlders have a core of sihcified limestone containing many shells and an outer shell

Character And Occurrence Of Deposits. 33

2 to 4 inches thick, formed of concentric bands of flint, differing slightly in color but usually some shade of blue.

The overburden at this pit consists of about 10 feet of coarse, yel- low sand, which is locally slightly indurated but is sufficiently friable to break up easily.

Another mine in this vicinity consists of two branches, about 150 yards long and 50 yards wide, with short lateral projections where the miners have been excavating. This rock is reported to average more than 77 per cent tricalcium phosphate and to overlie 7 to 8 feet of rock ranging from 61 to 65 per cent. This lower rock in turn rests upon limestone of the Vicksburg group, the contact between the two being very irregular.

At one point a mass of sand rock (sand horse) about 25 yards across was left after the phosphate rock was removed from around it. The pit is about 25 to 30 feet deep and the overburden consists of 10 to 12 feet of yellow stratified sand, which is slightly indurated except in the upper 3 to 4 feet.

Some of the mines in this part of the rock-phosphate region contain plate rock. One pit shows about 20 feet of phosphate consisting of small angular pebbles and some laie bowlders and plates embedded in a matrix of fine clay, mixed with more or less soft phosphate. The pit contains several large plates of phosphate, some of them being 8 or 10 feet wide before they are broken. In places the plates have been bent downward by movements in the phosphate deposit.

The overburden consists of 12 to 15 feet of yellow sand, sUghtly indurated near the base, containing some lenses and irregular masses of clay. The position of the lenses indicates that the deposit has been more or less disturbed, probably as a result of the solution of the underlying limestone and the falling of the roofs of caverns, resulting in slumping of the overlying phosphate. Fragments and bowlders of flint IJ to 3 feet in diameter occur at several levels.

Phosphate Of Alum. Bluff Fobmation (''Bedbock'').

The uppermost formation of OUgocene ago in southern Florida is the Alum Bluff, which is represented in the pebble-phosphate region by a magnesian limestone and marl containing granules and nodules of phosphate interbedded with more or less clay and pebble phos- phate. This formation, especially the hmcstone portion, is known to the miners as bedrock." The exposures in the phosphate mines are seldom more than 5 or 6 fe§t thick, though in the Coronet mine a well penetrated limestone of the Alum Bluff formation to a depth of nearly 30 feet. In this well a thin bed of clay was encoim- tered, and a layer of flint near the surface which contained a great many fossils, those listed on pages 14 and 15 having been

85816**— Bull. 604—15 3

34 Phosphate Deposits Of Florida.

identified from selected specimens collected at this locality. One or more small exposures of the ''bedrock" can be foimd in practically every pit in the land-pebble phosphate region, and these numerous exposures show that the rock is a moderately hard limestone or marl containing many dark-colored nodules and granules of phosphate, a few shark teeth, and many casts of shells. The limestone changes to a light-yellow sticky marl on weathering because of the presence of considerable earthy matter in the original rock. Beds of clay and pebble phosphate that accumulated during the deposition of the "bedrock" are inters tratified with the limestone and marl and in some places rest upon them. (See PL VIII, A and jB.) The best section of this portion of the Alimi Bluff formation was obtained in driUing a well at the phosphate mine near Medulla. The following record of this well was suppUed by Mr. North, foreman of the mine:

Section of well at phosphate mine near Medulla,

Overburden: Feet.

Sand 22

Marl 6

Pebble phosphate:

Phosphate 17

"Bedrock":

"Yellow joint clay" (yellow marl) 32

Blue limestone 30

Phbsphate interboddod with clay 60-70

Undetermined :

Blue marl, clay, and rock alternating to a depth of 760 feet.

Reference to this section will show that in the Alum Bluff forma- tion C'bedrock'O a thick interbedded layer of clay and phosphate was encountered. This phosphate has no commercial value, because it is too deeply buried to be mined, but it is of considerable scientific interest, for it shows that a great deal of phosphate accumidated as an original deposit in the Alum Bluff formation. In one of the pits of the Phosphat<> Mining Co:, west of Mulberry, a thin, irregular layer of blue clay containing phosphate nodides was observed inter- bedded with the limestone of the Alum Bluff formation (see PL VI, A and B), and a similar section was seen in one of the pits of the Pierce Phosphate Co., where the phosphate bed had a thickness of nearly 10 feet and had been mined to a depth of 6 feet below the superincumbent bed of limestone of the Alum Bluff. Tliis rock was of lower grade than that obtained from the overlying Bone Valley gravel, and considerable carbonate of hme was mixed with the phosphate. In one of the pits at Christina a phosphatized por- tion of limestone of the Alum Bluff formation projects 8 or 10 feet above the floor of the mine. In appearance it is much Uko the rock phosphate, and the fact that it was altered from the limestone

B. Coarse Semi -Indurated Pebble Phosphate.

Character And Occurrence Of Deposits, 35

is evident, because the texture of the original rock is preserved. Veins of phosphate that were evidently deposited in cracks in the rock may be seen in this phosphatized limestone. (See PL VIII, A.) Although the phosphatic limestone and phosphate nodules of the Alum Bluff formation are commercially important only in small areas, they are of considerable interest because of their relation to the overlying Bono Valley gravel, which is the source of the land-pebble phosphate. Detailed information concerning this "bedrock" is given on pages 39-44.

Phosphate Of Bone Valley Gravel Ob. Land-Pebble Phos-

Distinctive Features.

The Bone Valley gravel as the term was used in the Second Annual Report of the Florida Geological Survey was intended to include the coarse, sandy land-pebble phosphate and the associated sands. The name is used in a similar sense by Sellards in his report on the phosphates of Florida. At the time of the pubUcation of the earlier report the fact that there was another phosphate-bearing formation in the land-pebble region was not definitely recognized. During the progress of recent field work it has become evident that, S

though the Bone Valley gravel is the source of the phosphate in nearly

all the mines, there are a few mines that obtain a small amount of 5

phosphate from the formation lying unconformably beneath the J

Bone Valley gravel. It seems best to draw the line as sharply as

possible between these two formations, as the periods of their depo- sition were unquestionably separated by a considerable interval of ; time, and therefore it should be imderstood that the name Bone Valley gravel does not include these older phosphate-bearing beds. !

The surface of the land-pebble phosphate region is comparatively level, though minor undulations amounting to 15 or 20 feet are not imcommon and variations of 50 feet in the altitude occur near the larger streams. This upland lies generally between 125 and 150 feet above sea level. At many places in the phosphate region the sand associated with the pebble phosphate, and in some locahties the phosphate itself is overlain by younger sands. These sands resemble those below so closely that the two can with difficulty be distinguished except where there is some marked unconformity between them. In the Phosphate Mining Co.'s pit, west of Mulberry, the line of demarca- tion between the upper sands and the Bone Valley gravel below is marked by a lens of dark-colored organic matter. According to the

I Matson, G. C, and Clapp, F. G., A prelimJnary report on the geology of Florida, with special reference to the stratigraphy: Florida Geol. Survey Second Ann. Kept., pp. 138-141, 1903.

Sellards, E. n., A preliminary paper on the Florida phosphate deposits: Florida Geol. Survey Third Aim. Rept., p. 33, 1910.

B6 PHOSPHATE DEPOSITS OF FLORn)A.

accoxint given by the foreman at this pit the lens had a maximiun thickness of about 2 J feet and measured several feet across. Similar evidences of unconformity between the Bone Valley gravel and an overlying formation are seen at other points.

The pit at Christina shows several feet of interlaminated sands and days between the phosphate and the overlying sand. The contact of the bed of clay and sand with the underlying phosphate is more or less irregular, but the fact that the plane of contact is roughly par- allel to the planes of stratification of the phosphate suggests that there may have been continuous deposition with merely slight change in the charact<5r of the sediments. In some of the mines erosion has proceeded far enough to remove the phosphate and a portion of the ''bedrock," forming channels that have subsequently been filled with younger sands.

The Bone Valley gravel consists of rounded pebbles of phosphate embedded in a matrix of sand or clay overlain by varying thicknesses of loose or semi-indurated sand. The maximum thickness of tliis formation is probably more than 50 feet, but only about one-third of this thickness should be assigned to the phosphate.

The phosphate-bearing portion of the Bone Valley formation is a gravel containing rounded and subangular pebbles of phosphate of varjdng degrees of coarseness intermingled with more or less sand and clay. In general the deposit shows distinct stratification, some beds being wonderfully persistent over a distance of several hundred yards though others are lenticular and extend only short distances. There are numerous alternations of coarse and fine material and many of the layers are distinctly undulating. (See PI. VIII, B.) The wavy character of the stratification appears to be original, though in one or two mines there are evidences of sufficient deformation to cause slight faulting, which has brought the overlying sand into juxtaposition with the phosphate. The entire formation bears evidence of having been deposited in shallow water where conflicting cmrents gave rise to irregular bedding and rapid alternations of sedi- ments of varying coarseness. The color of the phosphate-bearing portion of the Bone VaUey gravel varies from nearly white to dark gray and the individual pebbles are white, yellow, brown, or black.

Animal Remains.

Practically aU the mines contain fragments of bones of both land and marine animals. There are many vertebrsB, both largo and small, and in a few places these are foimd in juxtaposition, suggesting that they were articulated and were probably still held together by liga- ments at the time of their deposition. In one mine four of these

Ij

Characteb And Occurrence Op Deposits. 37

vertebrae were found, end to end, and a fifth was only slightly dis- placed. Reports of finding complete skeletons of marine animals are common, but many inquiries have been made without bringing to light a single instance where a skuU has been associated with a skele- ton. The most common animal remains are the teeth of sharks and fish, but in addition the teeth of the horse, mastodon, rhinoceros, and manatee have been found. (See Pis. IX to XII, inclusive.) Several fragments of tusks of mastodons were observed, among them being one that measured over 13 inches in circumference. Water- worn fragments of phosphatized casts of shells, apparently derived from the erosion of the underlying formation, are common in many mines.

Quartz And Chert.

Pebbles of quartz and chert occur throughout the Bone Valley gravel. Many of these pebbles arc perfectly rounded and are com- posed of pellucid quartz ; others are partly rounded fragments of dark chert, such as may be found in many parts of the peninsula of Florida. In the pits of the Coronet Phosphate Co. worn fragments of siUcified corals occur in the phosphate. Among these a single fragment weighing over 25 poimds was observed, but most of them are much smaller. They show very little evidence of wear, which indicates that they have probably not been transported far from their sources; they were evidently derived by weathering and erosion from some portion of the Alum Bluff formation.

Overburden.

The overburden, as it is commonly termed, consists of brown to gray coarse sand, usually resting directly on the phosphate. It varies in thickness from 3 to 4 feet in the northern part of the region to over 30 feet in the southern part. This sand locally shows some induration, the cementing material varying in different places. In some mines it is largely iron oxide, which locally accumulates to form a coarse sandstone that is known as ''hardpan.* In many mines it is necessary to blast this hardpan in order to break it up so that it may be removed.

Size And Shape Of The Deposits.

The mined areas of Bono Valley gravel form only a small part of the whole deposit. The gravel is rather widely distributed, forming a continuous mantle for several miles, bufc it is not mined except in small areas of various shapes. The. factors that determine the loca- tions of mines are the quantity of phosphate that can be obtained, the amount of waste material that must be handled in exploitation,

38 Phosphate Deposits Op Florida.

the quality of the phosphate, and the distance of the deposit from a raihoad.

The quantity of phosphate obtainable is determined before plans are made to install machinery tor mining, and as there is considerable difference in the thickness of the beds at different places, as well as pronounced variations in* the percentage of phosphate pebbles, both the thickness and the pebble content of the gravel are carefully con- sidered. In addition it is necessary to take into accoimt the amount and character of the overburden. The cost of removing the over- burden varies greatly. Soft sand is most easily removed because it can be handled by hydraulic processes; indurated sand is more diffi- cidt to excavate, as it may require blasting, and if the fragments are too large to pass througli the pumps used in the hydraulic process it is necessarv to use steam shovels, which increases the cost.

The price obtained for the phosphate will be governed largely by its quality, for, other things being equal, the value of the phosphate will depend upon its content of phosphoric acid. The presence of considerable sand that can not readily be removed by washing the pebbles will lessen value, and if a large percentage of the oxides of iron and aluminum are present the value of the phosphate will be lowered by them.

After all these factors have been considered it is usually found that the area of material which can be profitably mined is rather small. However, the average size of the pits in the land-pebble phosphate region is several acres, and the maximum size exceeds 40 acres.

Thickness.

The pebble phosphate varies in thickness but not so much as the rock phosphate. The thickness of the workable deposits ranges from a few feet to 20 or 25 feet, and probably averages 10 to 12 feet. The thickness of the sands that overlie the phosphate ranges from a few feet to over 40 feet, and probably averages more than 15 feet.

LOCAL DETAILS. irOBTHEKir PART OF BEOION.

In the rock-phosphate region detailed sections of the deposits have very little significance, but in the land-pebble phosphate region, where the phosphate is in the form of a conglomerate, there is much greater uniformity in both the character and the thickness of the materials. The details of sections taken in different parts of a single mine may be unUkc, but the major features are similar and in most places the relations of the deposits to both the overlying and the sub-

A. Part Of The Tusk Of A Mastodon.

B. TOOTH OF A MASTOOON. J. S. NMhwil MuHum Caulof ut No. 721

Jawbone And Teeth Of A

CHAKACTER AND OCCtTRRENCE OP DEPOSITS. 39

jacent materials are constant. The following sections illustrate the occurrence and relations of the land-pebble phosphate in different parts of the region.

Sections in northern parts of region.

Overburden: Feet.

Dark-brown to black sand 2- 3

Brown aand with pebbles stained by iron oxide 3

Fine, white, sandy phosphatic marl 0-2

Phosphate:

Arranged in well-defined layers interbedded with lenses of coarser material. Associated with the phosphate are many fragments of bones and a few shark teeth.

Fine white clay with coarse pebbles of phosphate 2

Sandy white clay with medium pebbles of phosphate IJ

Blue clay with fine pebbles of phosphate 4- 5

Bro%vTiish clay with coarse pebbles of phosphate 2

Soft blue clay with small grains of dark-colored phosphate. . . 2- 4 "Bedrock": Light-gray marl weathering yoUow or brown and containing numerous pebbles of phosphate and casts of shells. Upper surface irregular 2-f

Overburden:

Yellow sand 2- 4

Indurated gray sand 4- 6

Phosphate:

Containing many shark teeth and worn fragments of corals.

Coarse phosphatic gravel mth layers of varying texture 3-6

Olive-greon clay with fine grains and small pebbles of phos- phate i- 3

"Bedrock": Light-gray to yellow limestone containing many pebbles of phosi)hate, merging to a soft, sticky marl containing similar pebbles and fossils. Some layers of the limestone arc silicified 4-10-f

Overburden:

Incoherent gray sand 3- 4

Semi-indurated yellow sand 12

Lens of interlaminatf d blue clay and gray indurated sand . . 0- 6

Phosphate:

Sandy light-gray matrix containing many pebbles of phos- phate 10

Fine blue clay with small pebbles and granules of phosphate . 2

"Bedrock ": Sandy yellow marl and limestone 2-\-

In this pit the surface of the bedrock is very luieven but less fos- siliferous than at some other locaHties. At one point the bedrock rises several feet above the floor of the pit and has been altered to a rock phosphate containing light-colored, irregular veins of the same material. The rock phosphate has the texture and the pebbles char- acteristic of the imderlying bedrock.

40 Phosphate Deposits Of Florida.

KXTIiBEE&Y AKD VICIKTT7.

Section in part of Prairie PebhU Phosphate Co J a mine, at Mulberry.

Overburden: Feet.

Gray sand containing some organic matter 2

Gray sand containing yellow and red stains 4-5

Gray sand 5

Brown sand with some iron concretions 2

Phosphate:

Alternating layers of fine and coarse sandy phosphate gravel . 8-10 Fine greenish-gray sand and clay with numerous small gran- ules and pebbles of phosphate 4

"Bedrock:" Light-yellow marl and limestone containing dark pebbles of phosphate 4+

A more detailed section of the lower part of the exposure in thin pit is given below:

Section in lower part of pit at Mulberry.

Phosphate: Feet.

Fine sandy phosphate with small pebbles 6

Coarse pebble phosphate, most of the pebbles dark colored. . J-1 Alternating layers of gray and green sandy clay with fine

phosphate pebbles 2

Gray sand with coarse phosphate 1-2

"Bedrock":

Dark-yellow phosphatic marl 1-2

Pale-yellow friable limestone yrith pebbles of phosphate 3-f

In the upper 4 feet of the phosphate there is some trace of indura- tion and the beds are slightly undulating. The coarse layer is very persistent, having a horizontal extent of over 500 feet. Variations of 3 to 4 per cent, more rarely 5 to 6 per cent, in the amount of tri- calcium phosphate have been noticed within a distance of 150 feet. Some of these variations accompany differences in color; the light- colored porous rock being usually of higher grade than the dark- colored heavy rock. However, the light-colored rock loses a much larger percentage of volume in washing than the dark.

Section in Phosphate Mining Co.s pit No. 3, about 2 miles west of Mulberry.

Overburden:

Gray sand with dark sandy loam at the top and locally a dark Feet.

layer, containing organic matter, at the bottom 2

Gray and yellow semi-indurated sand 12

Gray sand with a few iron concretions 0- 3

Brown semi-indurated sand 2

Phosphate:

Light-gray sandy pebble phosphate with alternating layers

of coarse and fine material 6

Light-blue clay containing many small pebbles and granules

of phosphate 6- 8

"Bedrock'': Light-yellow limestone containing phosphate peb- bles 4-f-

Character And Occurrence Of Deposits. 41

At one point in this pit a wedge of pink sand extends to a depth of over 5 feet into the phosphate. The upper portion of this body of sand is 10 feet across and it tapers to a few inches in width at the bottom. Many of the coarse layers of phosphate have marked inclinations amoimting to 3 or 4 feet in a horizontal distance of not more than 10 feet. The contact between the "bedrock" and the overlying phosphate is very imeven and apparently the "bedrock" was extensively weathered and eroded before the phosphate was deposited. There is a marked difference in the character of the over- burden on the opposite sides of the pit. On the north side the sand shows distinct lamination and is stained yellow by streaks of iron oxide. This part of the overburden has in places a thickness of about 15 feet. On the south side of the pit the same kind of material has a thickness of only about 2 feet and it is overlain by about 10 feet of coarse gray, poorly stratified sand. In the north wall of the pit there is a lens of black clay containing thin laminae of friable sand rock. This lens, which has a maximum thickness of about 6 inches, separates the overburden from the underlying phosphate. The lens is reported to have had a horizontal extent of over 15 feet and a maximum thickness of 2 J feet. In one comer of this pit the "bed- rock" presents an unusual section, consisting of yellow limestone with pebbles of phosphate, 1 to 3 feet; blue clay and fine sand with pebbles and granules of dark-colored phosphate, 6 inches to 3 feet; hard yellow limestone, 2-f feet. At this locality the fine-grained phosphate is interbedded with the limestone that forms the "bedrock."

Section in the Pierce Phosphate Co.s mine at Pierce,

Overburden: eet.

Loose gray sand 3

Indurated gray sand 20-25

Phosphate: Gray phosphate rock with uniformly coarse pebbles in

a fine sandy matrix 6-16

"Bedrock":

Fossiliferoufl yellow limestone 0-4

Light-blue clay with fine sand and small granules and pebbles of phosphate 6-10

In another pit near the one where the above section was observed the following section was exposed:

Section in the Pierce Phosphate Co.s mine at Pierce.

Overburden: Feet.

Light-yellow sand 3- 4

Indurated gray sand with siliceous concretions. Phosphate:

Coarse pebble phosphate with gray sandy matrix and several large bone fragmente 6- 8

Sandy blue clay with fine pebbles of dark-colored phosphate . 4-}-

42 Phosphate Deposits Of Flortoa.

"Bedrock": Feet.

Marly yellow limestone with phosphate pehhles 3+

Clay containing many pebbles of phoejhate 10

FO&T KEADE AKD VICOnTT.

Section in Palmetto Phosphate Co.'s mine No. 2, at Tiger Bay.

Overburden: Feet.

Loose gray sand dark colored near the top 4

Indurated brown sand with local layers of concretionary iron

nodules near the top 10

Phosphate:

Coarse sand containing laige phosphate pebbles, bone frag- ments, and casts of shells 2- 4

Fine sandy matrix with small phosphate pebbles and local

lenses of coarser material 8-10

Fine blue sand and clay with small phosphate pebbles 1-2

"Bedrock " : Yellow limestone containing phosphate pebbles 2+

Section in Palmetto Phosphate Co.s mine No. ly at Dominio7i.

Feet.

Overburden: Gray sand stained yellow by iron oxide 15

Phosphate:

Coarse sandy phosphate with some undulating layers 10

Fine blue to olive-green, thinly laminated clay containing

phoephatic sand 4

"Bedrock": Yellow limestone containing many pebbles of phos- phate and large shells 4-|-

At one point near the base of this section four vertebrae were found in place and the iGtf th was lying about 2 inches away. In one end of the pit the phosphate extends into the fine clay to a depth of over 5 feet.

Section in phosphate mine at Agricola.

Overburden: Feet.

Loose gray sand 2

Semi-indurated yellow sand 10

Fine-grained, indurated brown sand containing a little phos- phate 1- 6

Phosphate:

Coarse gray sand with large pebbles of phosphate. 2

Fine gray sand with small pebbles of phosphate 4

Coarse gray sand with large pebbles of phosphate 2

Fine blue clay and sand with small pebbles and granules of

phosphate 2

"Bedrock": Hard yellow marl and limestone with phosphate

pebbles and granules 2+

Tho upper surface of the bedrock is irregular and slopes as much as 4 or 5 feet in a horizontal distance of 50 feet.

Character And Occurrence Of Deposits. 43

Section in Charleston Mining Co.s mine No, 1, at Fort Meade.

O verb urden : Feet .

Loose gray sand 4

Semi-indurated gray and brownish-gray sand vrith some iron

concretions and local lenses of gray phosphatic marl 12-14

Phosphate: Light-blue and gray sand with numerous fine peb- bles of phosphate and a few lenticular layers of coarser peb- bles 12

"Bedrock": Coarse gray limestone weathering yellow and con- taining many casts of shells and pebbles of phosphate 5-1-

The upper surface of the limestone is irregular and at one point an old stream channel has been eroded across the deposit, removing the overburden, phosphate, and a portion of the '' bedrock.'' The channel has subsequently been filled by a deposit of gray sand.

Section at Dominion Phosphate CoJs mine, Dominion.

Overburden: Ft. in.

Loose gray sand 4

Brown to yellow semi-indurated sand 6-12

Blue clay containing iron stains and resting unconformably

on the phosphate 4

Phosphate : Gray phosphatic conglomerate with a sand y matrix . 8-12 , This conglomerate shows frequent alternations of coarse and fine pebbles in layers ranging from 1 inch to 3 or 4 feet thick. "Bedrock " : Yellow limestone 4+

At one point in this pit there is about 4 feet of gray phosphatic sandy marl at the base of the overburden. A tooth of a mastodon was found in this marl. The line of contact between the marl and the phosphate is uneven, as though the latter had been eroded before the deposition of the former.

Section in mine of the Phosphate Mining Corporation at Royster.

Overburden: Feet.

Loose gray sand 2-4

Semi-indurated brown sand with yellow stains due to iron

oxide 10-12

Phosphate:

Sandy gray conglomerate with phosphate pebbles and a few

scattered bone fragments 6- 8

Blue to gray sand containing small pebbles and granules of

phosphate with some thin layers of coarser pebbles 5-6

Bedrock " : Sticky yellow marl with many pebbles of phosphate . 5 +

The stratification of the phosphate conglomerate is wavy and its upper surface appears to have been slightly eroded, for it bears channels from 1 to 2 feet deep, which have been filled with the sand of the overburden. In some places there is a thin layer of marly day at the contact between the overburden and the phosphate. A

44 Phosphate Deposits Of Florida.

piece of the jawbone of a mastodon containing a single tooth was found in this conglomerate. At one place in this pit a small piece of charcoal was embedded in the phosphate conglomerate. The section of material overlying this charcoal included 6 feet of phosphate conglomerate and 16 feet of sand overburden.

Section in the Tilghman Phosphate Co,* 8 mine at Bowling Green.

Overburden: Ft. in.

Loose gray sand 2- 4

Indurated gray sand 10

Thin, laminated blue clay 4

Phosphate:

Gray sand with coarse pebbles of phosphate 4

Gray phosphate conglomerate containing some sand 4

Blue clay and fine sand with many granules and small peb- bles of phosphate 1- 2

"Bedrock": Yellow limestone, locally phosphatic, and with some layers silicified 3+

Phosphatic Makl.

Character And Uses.

In some of the mines a soft, white phosphatic marl rests upon the Bone Valley gravel. The contact of the marl and the gravel, is as a rule sUghtly iwegular, and the marl itself is generally intermingled with more or less sand similar to that which forms the overburden. This marl has been mined in the vicinity of Fort Meade and, after burning, is reported to contain a high percentage of tricalcium phos- phate. The output of this mine is \ised in making fertihzer. The marl in the pebble-phosphate mines is not regarded as valuable and is removed with the sand that forms the overburden. Animal re- mains are rare in this marl, but it was in material of this kind that Superintendent Campbell of the Dominion Phosphate Co. found the mastodon tooth mentioned by Sellards in his report.*

Section in the International Phosphate Co.s viine, Jane Jay.

Overburden: Peet.

Loose gray sand containing many pebbles and fragments of

phosphatic marl 2- 4

Sandy, gray phosphatic marl resting upon an uneven surface

of phosphate gravel 2- 4

Phosphate:

Gray sand alternating with layers of coarse and fine phosphate

pebbles 10

Thin, laminated, olive-green clay containing fine phosphate

pebbles 4

"Bedrock": Light-yellow limestone and marl with phosphate pebbles 2-f-

Sellards, E. H., A preliminary paper on the Florida phosphate deposits: Florida Geol. Survey Third Ann. Kept., p. 24, 1910.

Origin And Age Of The Phosphates. 45

The limestone has an uregular upper surface and was apparently extensively weathered before the deposition of the phosphate. Eroded casts of shells showing considerable abrasion, which were doubtless reworked from the 'bedrock," are numerous in the upper portion of the phosphate deposit.

Development At Fort Meade.

A deposit on the west bank of Peace River consists of coarse gray phosphatic marl containing a large amoimt of sand like that described as phosphatic marl in connection with the discussion of the over- burden in the Pebble Phosphate Co. 's mines. The rock is quarried and burned for use in making fertilizer.

Section in pit on west hank of Peace River.

Overburden: Feet.

Brownish-yellow sand containing fragments of phosphatic marl . 2

Yellow sand with pebbles and fragments of phosphatic marl. . 2- 3

Phosphate: Sandy, gray phosphatic marl 10

Biver-Pebble Phosphate.

The river-pebble phosphate, as the name impUes, is a fluviatile de- posit consisting of pebbles of different sizes arranged in bars and lenses of various sizes and shapes. The fragments of phosphate show roimded outhnes produced by mechanical abrasion and range from small granules to pebbles 2 inches or more in diameter, though the average diameter is less than an inch.

The phosphate is usually stained dark by a surficial coating of organic or, more rarely, inorganic matter, and the pebbles when broken show colors similar to those of the land-pebble phosphate. The deposits contained many fragments of bones and teeth of sharks and other animals. Presumably the ''Peace Creek bone bed," already mentioned, belongs to the river-pebble phosphate, though there is little or no definite information concerning the source of the collections of vertebrate remains that were assigned to this bed.

The matrix of the river-pebble phosphate consists of sand and sandy clay of various colors. The sand predominates and is in places so coarse that it is difficult to separate from the phosphate. In some localities, as on Miakka and Caloosahatchee rivers, there are so many shells of marine organisms mixed with the phosphate pebbles that mining is impracticable.

Origin And Age Of The Phosphates.

General Concx.Tjsions.

The phosphates of Florida occur in sedimentary rocks and with the exception of certain deposits southwest of Lakeland are of second- ary origin, having been redeposited either by mechanical or chemical

46 PHOSPHATE DEPOSITS OF FLORmA.

action. They are of Tertiary age, the rock phosphates occupying depressions in the surface of limestones of lower Oligocene age and the pebble phosphates being somewhat younger. The land-pebble phosphates have been assigned to the Miocene, though they may possibly be as late as early Phocene. The river-pebble phosphates are in part Pleistocene and in part Recent. They occur in beds of streams that flow through the phosphate region or they lie beneath the low terraces that border these streams.

Phosphate deposits similar to those found in Florida have been reported from many other localities, and the studies of Sir John Murray have shed much Ught on the origin of types of phosphate analogous to those occurring in some parts of the State. His discus- sion of the origin of marine phosphates is of unusual interest, and further reference to his work will be made on subsequent pages. Various theories have been advanced to explain the origin of the rock phosphate of Florida, and these will here be reviewed.

BOCK PHOSPHATES OF THE VICESBXTIta aBOTTP.

Theories Of Origin.

One of the early theories to account for the origin of the rock phos- phate of the Vicksburg group was advanced by Millar,' who cites the opinions of Darton and others, with comment, as follows:

Mr. N. H. Darton, of the United States Geological Survey, is, among others, of opinion that guano V7as probably the original source of the phosphate deposits, and this theory seems to cover the conditions of the problem more completely than most of the hj'potheses advanced. Others again consider that the underlying limestone rock originally contained a certain i)ercentage of phosphate of lime, and that by the action of water the carbonate got leached out, leaving behind a crust of phosphate of lime. The objection to this theory is the tremendous leaching out of carbonate of lime which would have to have taken place in order to leave behind so thick a bed of phosphate. For, supposing even that the limestone actually did contain 5 per cent of phosphate of lime, this would mean a leaching of a thickness of 1,000 feet of limestone to produce 50 feet of phosphate.

A third theory is that the upper surface of the limestone rock, being continually washed with phosphate in solution, derived from the decomposition of animal remains, gradually lost its carbonic acid and became phosphatized. In this case one would expect to find phosphatized shells, which up to date have not been forthcoming.

Dr. Francis Wyatt considers that the phosphate formation was due to the evaporation of the Miocene waters.'

"During the Miocene submergence there was deposited upon the Upper Eocene lime- stones, more especially in the cracks or fissures resulting from their drying up, a soft, fine disintegrated calcareous sediment or mud.

"The gradual evaporation of these Miocene waters brought about the formation, principally in the neighborhood of the rock cavities and fissures, of large and small

1 B.ex>ort on the specimens of bottom depasits dredged by U. S. Coast Survey steamer Blake: Mas. Comp. Zoology Bull., vol. 12, 188.'>-86, pp. 37-61. Deep-sea deposits: Keport on the sclent iQe results of tte voyage of H. M. S. ChalltnffeTtVP- 391-400, London, 1891.

2 Millat, C. C. H., Florida, South Carolina, and Canadian phosphates, pp. 11&-118, 1892. s Eng. and Min. Jour., Aug. 23, 1890.

Obigin And Age Of The Phosphates. 47

estuaiiee. These estuaries were replete, swarming with life and vegetable matter — fish, mollusks, reptiles, and marine plants. They were, besides, heavily chaiged with gases and acids, and their continuous concentration ultimately induced a multiplicity of readily conceivable processes of decomposition and final metamorphism."

Dr. N. A. Pratt, on the other hand, is of opinion that the rock or bowlder phosphate had its immediate origin in animal life, and that the phosphate bowlder is a true fossil. He does not see any objection to the possibility of a species existing which secreted a skeleton of phosphate of lime, in the same way that the coral animal secretes carbonate of lime. He thinks, in fact, that such a species did exist, and that the fossil bowlder is the fossil remains of a huge foraminifer, which had identical composition in its skeleton with true bone deprived of all organic matter.

These are the principal theories as to the origin of the phosphates, and there are as many or more hypotheses accounting for the formation in which the phosphate is found to-day. Without discussing these in detail, it seems to be agreed that the deposits owe their present position and form to the agency of water; in other words, the phosphate is not found to-day in the position and shape in which it originally received its origin, but the beds or crusts or layers have been broken up, washed together, detrited, water, worn, and rolled by the action both of salt and fresh water until their present form and position were arrived at.

Dall suggests that the rock phosphate is the result of the action of solutions bearing phosphoric acid upon limestone. He thinks the occurrence of bones and teeth in the phosphate has no bearing on the origin of the deposits, and the phosphoric acid, according to his theory, was supplied by the leaching of excreta of birds, seals, or other gregarious animals.

The local character of such rookeries would determine the local occurrence of phos- phate rock, whoso irregularities in this respect are notorious. The different forms under which the phosphates now present themselves would result from the different constitution of the rocks upon which the rookeries were originally situated; the differ- ence in elevation and dryness or accessibility to occasional incursions of brackish or salt water; the existence or nonexistence of some subterranean water table in the par- ticular localities; and subsequent solutionary or erosive action upon the rocks thus modified. The material of such rocks rearranged into later strata would preserve a certain proportion of phosphoric acid, even though no subsequent additions of that substance were received by the new beds. A tendency under certain circumstances for the phosphatized lime to concentrate in nodules, or as shells over harder nuclei, is very marked. In this process it "vould seem as if the traces of iron in the rocks foL lowed and joined with the phosphoric acid, since these nodular concretions are almost invariably darker colored than the rest of the rock, and. when subjected to river action, frequently become blackened by the resulting chemical action on the contained iron.

Pratt, whose views are outlined in the report of Millar, already quoted, suggests that the bowlders are the skeletal remains of gigantic Foraminifera that flourished at the time the rock was being deposited. The rock phosphate was thought to have been derived from the skeletons of these animals, and the soft phosphate was attributed to the spawn.

1 Dall, W. H., and Harris, O. D., Correlation papers— Neooene: U. S. Geol. Survey Bull. 84, pp. 134- 140, 1862.

48 Phosphate Deposits Of Florida.

Eldridge/ in 1892, published a comprehensive discussion of the origin of the rock and soft phosphates. In considering Eldridge's paper it should be borne in mind that the rocks called Eocene are now placed in the Vicksburg group, and that his phosphatized ''Mio- cene" is now included in the Apalachicola group; both therefore be- long to the Oligocene. Eldridge divides the formation of the rock phosphate into three periods: (1) Formation of the primary rock by replacement of the carbonic acid of the original limestone by phos- phoric acid, thus changing the calcium carbonate to calcium phos- phate; (2) secondary deposition of phosphate both from solution and suspension in cavities in the primary rock; (3) disintegration and re- deposition of the phosphate. This author mentions both the altera- tions of limestones by solutions bearing phosphoric acid from guano beds and by concentration of phosphate present in the limestone as an original constituent, but makes no attempt to discriminate between the two possible sources of the phosphoric acid. He believes that there is clearly evidence of downward percolation of surface waters —

highly charged with carbonic and earth acids, and thus enabled to carry down into the mass of the limestone dissolved phosphate of lime, to be redepoaited under con- ditions favorable to its separation. Such conditions might have been brought about by the simple interchange of bases between the phosphate and carbonate of lime thus brought together or by the lowering of the solvent power of the waters through loss of carbonic acid. The latter would happen whenever the acid was required for the solution of additional carbonate of lime, or when, through aeration, it should escape from the water. The zone of phosphate deposition was apparently one of double concentration, resulting from the removal of the soluble carbonate, thus raising the percentage of the less soluble phosphate, and from the acquirement of additional phosphate of lime from the overlying portions of the deposit.

Much of the primary rock, both Eocene and Miocene, has the appearance rather of deposition by precipitation than of alteration by replacement of the limestone by the phosphate, but either of these processes may have taken place under the conditions existing at that time.

The secondary period of Eldridge includes deposition by chemical precipitation either on exposed surfaces or in cavities and crevices, together with deposition of phosphatic sediment from suspension in the waters percolating through the phosphate deposits. During this period the incrustations in cavities and the laminated and plate- shaped deposits that now appear as bowlders were formed. Lami- nated phosphate is also attributed to repeated deposition of a thin coating of phosphate on a sea-washed shore, the precipitation being caused by aeration resulting in a slight loss of carbonic acid. In the period of secondary deposition are included the examples of rece- mentation of broken fragments of phosphate giving rise to brecciated forms.

1 Eldridge, Q. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., vol. 21, pp. 21-218, 1892.

Origin And Age Of The Phosphates. 49

Duriiig the third period of formation of rock phosphates, as out- lined by Eldridge, the beds previously formed were broken up and redeposited in their present position with detritus from various sources. When this action occurred is uncertain, but it was probably during the time of the last submergence of the peninsula, when con- ditions were believed to have been especiaUy favorable to the solution and abrasion of the limestone upon which the phosphate rested. The soft phosphate found associated with the bowlders is thought to have been derived from hard rock phosphate by processes of com- minution of bowlders and pebbles.

Types Of Rock Phosphate Discriminated.

Failure to discriminate between the rock phosphates in the lime- stones of the Vicksburg group and those in the limestones of the Apalachicola group has led to much confusion, for these deposits differ not only in age but in mode of occurrence and origin. It has already been noted hero that all the rock phosphate now mined rests on the limestones of the Vicksburg group, and it may be added that a large part of the soft phosphate either occurs with this rock phosphate or occupies depressions in the upper surface of limestones of the same age. In the previous discussion the rock phosphates of the Apa- lachicola group have been disregarded because the only deposits of that group that are now readily accessible are those belonging to the Alum Bluff formation C' bedrock'' of the miners) of the pebble- phosphate region.

The phosphates described by Eldridge as belonging to the Eocene system rest on the limestones of the Vicksburg group. A careful examination of these deposits shows that though they include mate- rials of various kinds mixed together in a more or less heterogeneous mass, they can be separated into two types, which may either occur in different mines or be found together in a single mine.

Rock Phosphate Formed In Place.

Phosphate of the first type is represented by such deposits as the one at the Cummer Lumber Co.'s mine a mile south of Newberry. The phosphate at this mine consists of angular fragments, such as the miners ordinarily call pebbles, associated with bowlders, the largest having a diameter of more than 18 inches and the whole being inclosed in a matrix of soft phosphate and clay. Most of the pebbles and bowlders are phosphatic, though a few of the bowlders are of flint.

Eldridge, G. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., vol. 21, pp. 213-218, 1892.

85816**— Bull. 604—15 4

50 Phosphate Deposits Op Florida.

The deposit includes a few pebbles of partly phosphatized limestone, and in some places near the contact with the underlying rock there is a transition zone from the phosphate to the limestone. Fossils are rare in such deposits, though in a few places phosphate pebbles and bowlders containing Vicksbm*g fossils have been seen (see PI. XIV, 5), and fragments of bone and teeth of sharks are distributed sporadically throughout the phosphate. In the transition zone frag- ments of Orbitoides and other characteristic fossils of the limestone may be found, but owing to the pulverulent character of the partly phosphatized limestone the contact phenomena may easily be over- looked. The surface of the limestone appears smooth after the phosphate has been reriioved, and this fact led Sellards to conclude that a portion of the limestone had been removed by erosion prior to the deposition of the phosphate. The irregular outline of the lime- stone bears some resemblance to an eroded surface, but the channels are not continuous, and the presence of rounded depressions of small diameter (see PI. XIII, A and 5), locally called wells," some of which extend several feet into the limestone, can hardly be explained by assuming that they are due to erosion.

Deposits of the character just described appear to have been formed in place by alteration of calcium carbonate to calcium phosphate under the influence of solutions bearing phosphoric acid. In this process nearly all the fossils are destroyed and the texture of the original rock is at many places altered beyond recognition, though not everywhere, because at a few locahties both the characteristic fossils and the texture of the rock have been preserved during the process of phosphatization. Apparently the phosphate accimiulated in unusually large quantities about certain centers, producing phos- phate pebbles.

The nature of the process by which the formation of phosphate Hodules was begun is not known, but after a nodule had been started the accumulation was due, in considerable measure, to the attraction of the material already deposited. Variations in the density of the limestone may have been the primary cause of the formation of centers of unusual accumulation, but as the texture of the original rock has been obliterated this theory can not be readily proved.

Some of the bowlders appear to have been formed by deposition of phosphate in preexisting cavities and channels in the limestone, the accumulation beginning as a coating on the walls of the openings, and therefore they conform in outline to the shape of the cavities in which they were deposited. At many places changes in the character of the solution produced successive layers of sUghtly different colors, and in many cavities the phosphate was more or less definitely arranged

1 Sellards, E. H., A preliminary paper on the Florida phosphate deposits: Florida Geol. Survey Third Aim. Kept., p. 24, 1910.

To Undehlyins Lime.

N OF CUMMEB LUMBER CO.'S MINE AT NEWBERRr,

52 Phosphate Deposits Op Florida,

carbonate in solution, the phosphate already formed being left in on incoherent mass. Thus some of the soft phosphate is slightly ce-

Jl & herent and its texture resembles

1 1 ". that of the phosphate of the Vicks-

I burg group, but this type is com-

Ij a paratively rare. Large quantities

Z of soft phosphates can hardly be

" formed by mechanical destruction

of rock phosphate except where § the fragments of such phosphate g have boon subjected to enough at-

trition to produce rounded forms.

HEDEPOSrPED PlfOSPirATE.

S Another type of rock-phosphate

I deposit found on the rocks of the

Vicksbui group is illustrated by

a section seen in a mine near

I, Newberry. The phosphate peb-

bles at this mine show evidence of

-g abrasion, and many of them are

g- well rounded. There is an absence

s of laie bowlders in the upper

s portion of the deposit, and the peb-

3 bles show a general arrangement

I in layers. The matrix is pre-

I vailingly sandy, though m places

it contains much clay aud soft

I phosphate. Thm layers of sand

I are mterbedded with the phos-

phate. This type of deposit is

I shown in figure 2. That sucb a

deposit is the result of erosion and

M redeposition of preexisting phos-

1 phates can hardly be questioned. There is little doubt that both

-a I soft phosphate and pebbles were

„ derived from deposits formed in

I j; tlie places where they are found,

'C\-:\ S though additional soft phos-

2 phate was formed by mechanical wear during the ])roces3 of trans- portation of the pebbles, aud some

of the pebbles were derived from geologic formations younger than

i E s i

M

£ I

Origin And Age Of The Phosphates.

the Vicksburg group. The relatively small proportion of soft phos- phate and the large quantity of

'.

sand in the matrLx is due to the fact that the soft phosphate was not deposited in the waters that laid down the phosphatic grav- point where quieter water fa- vored the deposition of fine- grained material.

Though care has been taken to separate the discussions of the two types of phosphate, it should be clearly understood that both types may be found in the same mine, and even in a single section. Thus in many places the phosphate deposits are a composite of materials formed in place and other ma- terials that have been redepos- ited. Where the two types occur in the same section the phosphates formed in place are naturally found beneath those that have been redeposited. Both types have been subjected to the same kinds of disturbance and their discrimination is in many places uncertain because at some localities where there has been considerable move- ment, resulting from solution and removal of the supporting limestone, the deposits have been reduced to a heterogene- ous mass that preserves very little of the original structure.

Source Of The Phosphoric

Ach).

There are three probable sources of the phosphoric acid of the rock phosphate — first, the phosphate originally disseminated through the limestone; second, the

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s

S .9

esto

- r 8

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9 vH

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i

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to

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54 Phosphate Deposits Of Florida.

phosphate contained in organic matter accumulated on the surface of the limestone; third, the phosphate derived from post-Vicksburg formations.

The best statement of the theory that the phosphoric acid was originally contained in the limestone of the Vicksburg group was made by Brown/ who argues that the phosphoric acid was originally disseminated through the limestone chiefly in the form of nodules and in shells of phosphate-secreting animals. He assigns to leaching of phosphoric acid from guano a subordinate place in the process of formation. Some of the phosphoric acid was concentrated by solu- tion and redeposition, replacing the carbonic acid of the limestone. Disintegration of the rock containing the phosphate nodules freed them from the surrounding Umestone, and they were subsequently washed into sinks and channels either by streams or ocean currents, or by both.

Cox mentions the possibiUty that some of the phosphoric acid may be original but does not elaborate the theory, .evidently believ- ing that guano was a more abundant source.

Though analyses are not at hand it is well known that the Vicks- burg rocks, as well as some of those belonging to the Apalachicola group, contain small quantities of phosphoric acid. An objection to this theory is offered by Millar, who says that. even if the limestone contained 5 per cent of phosphate of lime — a very large estimate — it would require the leaching of 1,000 feet of hmestone to produce 50 feet of phosphate. Though the average thickness of the rock phos- phate is small, a fatal objection to the theory of concentration is found in the sporadic distribution of the rock phosphate in patches a few acres in extent, unless the phosphates that remain are regarded as small remnants left by the erosion of deposits that once covered much larger areas. This theory would explain the present distribu- tion of the phosphate if surface erosion had predominated, but the removal of the limestone of the Vicksburg group is now, and probably always has been, chiefly the result of solution, mechanical abrasion having been relatively unimportant. Thus it is necessary to seek some explanation of the concentration of the phosphate in deposits. If it is assumed that phosphate accumulated in large quantities at different places in the rock, its distribution would be accounted for, but the form of the deposits and their relation to the limestone would still be unexplained. The explanation of the mode of concentration given by Brown seems plausible, but no such accumulation of

1 Brown, L. P., Phosphate deposits of the Southern States: Eng. Assoc, of the South Trans., vol, 15, No. 8, pp. 63-6C, 1904.

Cox, E. T., Floridito: A new variety of phosphate of lime: Am. Assoc, Adv. Sci. Proc., vol. 39, pp. 2C0- 262, 1801.

s Millar, C. C. H., Florida, South Carolina, and Canadian phosphates, p. IIG, 1892.

Op. cit., pp. 6a-66.

Okigin And Age Of The Phosphates. 55

nodules and phosphatic shells as would be necessary to supply the phosphoric acid has been noted in the Vicksburg group of limestone.

The geologic relations of the rock phosphate are explained by the theory advanced by Dall and others that the phosphates are the result of phosphatization of limestone by percolating waters bearing phosphoric acid in solution. Such solutions would act more efficiently where the conditions governing the circulation of the water were favor- able, and thus in some places the alteration would take place along irregular zones, whereas in other places the greatest change would occur along more or less rounded channels. That the fundamental movement of phosphate was downward is shown by the narrow bodies of phosphate that extend into the limestone, which indicates that the alteration occurred when the water table was below the level of the zone of phosphatization, as otherwise circulation would have been more nearly horizontal and the alteration would have pro- duced nearly horizontal bodies of phosphate, which might easily have been mistaken for bedded deposits. Probably the presence near the surface of relatively impermeable argillaceous limestones explains the localization of some of the deposits.

The soTirce of the phosphoric acid has been regarded as guano accumulated in the rookeries of birds, seals, or other gregarious animals. Probably this theory would be strengthened by assuming that these rookeries were those of birds that occupied small islets when the land stood near sea level, though it is probable that marine animals, both by their excreta and by their remains, would be the source of some of the organic material.

The fact that a very large quantity of guano would be required to furnish the phosphoric acid in the extensive accumulations of rock phosphate has been urged as an objection to this theory; but though phosphoric acid forms only about one-eighth of undecomposed guano, the objection is not conclusive. The strongest argument against the theory is found in the relation of the phosphate to the Oligocene formations. If we assume that the guano accumulated on scat- tered islets or in embayments during the emergence of the limestones of the Vicksburg group before the deposition of the Apalachicola sediments it would have been buried beneath the formations of the Apalachicola group. This conclusion is necessitated by the fact that the entire area included in the rock-phosphate region was covered by these formations, for though they have since been removed their

Dall, W. H., and Harris, G. D., Correlatioii papers— Neocene: U. S. Geol. Suney Bull. 84, pp. 134-140, 18)2.

Dall, W. H., op. cit. Wyatt, Francis, Notes on Florida phosphate beds: Eng. and Min. Jour., vol. 50, pp. 218-220, 1890. Darton, N. H., Notes on the geology of the Florida phosphate deposits: Am. Jour. Sci., 3d ser., vol. 41, pp. 102-105, 1891. Johnson, L. C, Notes on the geology of Florida; two of the lesser but typical phosphate fields: Am. Jour. Sci., 3d ser., vol. 45, pp. 497-503, 1893.

56 1>H0Sphate De10Sits Of Flobida.

detritus covers the surface and their remnants form a nearly con- tinuous rim around the phosphate region and rise from 50 to 100 feet above it. Well borings, however, do not show any accumu- lations of phosphate beneath these formations, and prospect holes show that near the contact of the Vicksburg group with the younger formations the phosphate deposits thin rapidly and the rock phos- phate beneath the younger formations is the result of replacement such as might be expected where solutions bearing phosphoric acid penetrated the porous limestone. Any theory requiring the accumu- lation of guano upon islete during the period mclpding the resub- mergence of the Vicksburg group of limestone and the beginning of Apalachicola deposition would be subject to the same objection and would be further invalidated by the fact that at some localities the limestone was replaced to depths of 25 feet or more above the level of ground water. The islets of limestone must therefore have stood several feet high for a period long enough to permit the transfor- mation of the original rock to phosphate.

There still remains the possibiUty that guano was deposited sub- sequent to the deposition of the Apalachicola sediments. Against this possibiUty it may be urged that the temperature in this region was lower, as shown by the fossils of the post-Oligocene Tertiary, being about the same as that now prevailing between the latitudes of Cape Hatteras and Chesapeake Bay, and the conditions were therefore less favorable to the existence of large numbers of birds or marine animals. A still greater obstacle is found in the fact that the localization of the deposits of guano requires that some con- dition, such as a nearly complete submergence, should restrict the area available for rookeries, if birds were the source of the guano, otherwise no large quantity would accumulate in one place. The fact that the limestone was exposed only where the overlying sands and clays had been removed, and once exposed was more readily removed than the sands and clays of adjacent areas, caused the Vicksburg rocks to occupy the depressions, whereas the later Oli- gocene formations occupied the higher lands. After a submergence the favorable situation for rookeries of birds would be on the hills, which would project as islands when the adjacent valleys were filled with water. But these islands would be composed of sands and clays of the Apalachicola group, and would not be subject to phosphatiza- tion such as we find in the rock-phosphate mines. The absence of a general submergence in post-Oligocene time would also be a fatal objection, for it would preclude the possibiUty that the phosphoric acid had been derived from the remains and excreta of gregarious marine animals.

Obigin And Age Of The Phosphates. 57

A recent paper by Sellards presents a somewhat different view of the source of the phosphoric acid. According to this author the upper Oligocene formations which formerly extended across the rock- phosphate region supplied the phosphoric acid. The deposits con- tain fragments of the younger formations, together with phospha- tized portions of limestone of the Vicksburg group.

Concerning the validity of the conclusion that the upper Oligocene fonnations formerly covered the phosphate regions there should be unanimity of opinion among those who are familiar with the geology of Florida. The younger formations surround the phosphate region by nearly continuous outcrops on the east, the north, and the south and are represented by outhers on the west. They rise on the east to an altitude somewhat above the surface of the phosphate region, and residual products of them are found on the surface of limestone of the Vicksburg group in the area where the phosphate occurs. The upper Ohgocene formations are phosphatic, a notable percentage of phosphate nodules being ound in the Aliun Bluff formation (' bedrock") of the pebble-phosphate region, in a quarry near Hawthorn, in a sink near Brandon, in the outcrops on Sopchoppy River, and at many other localities. The formation of the phosphate nodules in the upper Ohgocene will be discussed in considering the phosphates of the Alum Bluff formation, but it may be said here that they are of marine origin.

A clear understanding of this theory concerning the source of the phosphoric acid in the hard-rock phosphate necessitates a brief consideration of the post-OUgocene history of the region. The upper Oligocene rocks were at first eroded by surface streams, but wherever the underlying limestone of the Vicksburg group was so near the surface that the ground water penetrated it freely, solution resulted in the formation of imdergroimd channels and sink holes. These depressions received the wash from the surrounding areas, which induded some phosphate nodules, and at the same time some water containing phosphoric acid, dissolved from the overlying beds, per- colated into the limestone of the Vicksburg group. The action of such solutions upon the limestones resulted in their alteration to calcium phosphate by an interchange of phosphoric acid for the car- bonic acid of the limestone. Examination of thin sections of rock phosphate shows that some of the material contains much more quartz, in the form of sand grains, than is found in the limestone of the Vicksburg group. Such fragments resemble the phosphate nodules of the Almn BluflF formation. Other sections are relatively free from sand, and the rock is probably phosphatized limestone of

1 Sellards, E. H., Origin of the hard-rock phosphate deposits of Florida: Florida Qeol. Survey Fifth Ann. Rept, pp. 23-, 1913.

58 Phosphate Deposits Of Flobida.

the Vicksburg group. In addition, there are bowlders of more or less completely phosphatized limestone containing Vicksburg fossils. Some of the deposits appear to have been formed in the places where they lie, the phosphates being the result of alteration of the hmestones ; others have been reworked and are a composite of material derived from both Vicksburg and post-Vicksburg formations.

Phosphate Of Alt7M Blx7Ff Fobjcation (<<Bedeock").

Marine Phosphatic Nodules.

While the Alum Bluflf formation was being deposited a large amount of phosphate accumulated in some of the hmestones and associated clays. The most valuable deposits of the Apalachicola group examined during the investigation made for this bulletin belong to the limestone and associated clays of the Alum Bluff formation ("bedrock") southwest of Lakeland, but phosphates of the Alum Bluff formation have been mined at Hawthorn, and at other places, as at the Devils Mill Hopper,* in Alachua County, and on Aucilla River southeast of Tallahassee.' Little is known, how- ever, concerning any of these phosphates except those in the area southwest of Lakeland, and the discussion will therefore be confined to the deposits of that area.

The occurrence of phosphate granules and nodules embedded in the limestones and interbedded clays of the Alum Bluff formation has been noted in the discussion of the phosphates of the Alum Bluff formation, on pages 33-35. The amount of this material is large and it appears to be widely distributed, though it forms a relatively small proportion of the whole formation. The Alum Bluff formation ("bedrock") is found in every pebble-phosphate mine, and the well at Christina showed a thickness of phosphate beds exceeding 60 feet.

The phosphatic granules are very abundant at certain horizons and where granules of dark and light colors arc mixed together they give the motthng that prospectors call ''pepper and salt." In general these granules differ considerably in size, ranging from particles invisible without the aid of a lens to well-defined grains larger than a pea. Most of them are smooth ovules, though some are globu- lar, or kidney shaped, or have other forms. The nodules of phosphate have the same general distribution as the granules, but differ from them both in size and shape. In addition to being larger most of the nodules have more or less irregular outhncs, though they are not angular. They show many rounded protuberances and cavities,

Dall, W. H., and Harris, G. D., Correlation papers— Neocene: U. 8. Geol. Survey Bull. 84, p. 108, 1802. Eldrldge, G. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., vol. 21, p. 197, 1803.

Okigin And Age Of The Phosphates. 59

but the surfaces of the nodules are usually so smooth that they appear to have been polished. Both light and dark nodules occur, but the dark ones predominate. On polished surfaces and in thin sec- tions the nodules are seen to inclose granules of phosphate showing characteristic forms and colors, together with somewhat angular grains of quartz and, more rarely, of other silicate minerals. Some of the nodules consist of an outer shell of dense phosphate surrounding a bit of limestone that still retains its original texture and contains characteristic fossils, which may be either partly or wholly represented by casts of phosphate. Around this limestone and its inclusions is a thin shell of brown or yellow phosphate, which forms the outer s\ir- face of the nodule. The limestone in some nodules is penetrated by reticulated masses of phosphate, which project inward from the outer shell; the limestone in others has been entirely changed to phosphate. In thoroughly phosphatized nodules the texture of the limestone is not invariably preserved, and the fossils are usually destroyed, though in some nodules the imprints of shells may be seen. The inclusions of phosphate granules and quartz grains show a tendency to aggregation, but the aggregation probably occurred before the rock was phosphatized. Cracks or other openings in the limestone have usually been filled by a secondary deposit of phos- phate that shows bands of slightly different colors, and some cavi- ties that are not entirely filled have botryoidal surfaces.

The granules and nodules of phosphate are distributed through a considerable thickness of the Alum Bluff formation and are more abundant in some layers than in others, a fact indicating that phos- phatic material was supphed intermittently. Their association with limestone, clay, and sand shows that they accumulated in both clear and muddy water.

The phosphate granules and nodules of the Alum Bluff formation (**bedrock") bear a striking resemblance to those described by Sir John Murray as occurring on the sea bottom. Concerning specimens obtained from the sea floor between Cape Hatteras and lat. 31° 4' N., this author says:

Phosphate of lime and manganese concretions are present in all the deposits, and one remarkable concretion of these substances is described in detail from station 317, in a depth of 333 fathoms, immediately imder the waters of the Gulf Stream.

In deposits dredged from the Gulf of Mexico and the Florida Strait concretions of calcium phosphate were very numerous. The character of these concretions is indicated by the following extract:*

Pho8phatic concretions. — The phosphatic concretions in the dredgings in Florida Strait are very interesting. In a great many deep-sea deposits there is usually a

1 Report on the specimens of bottom deposits: Harvard Coll. Mus. Comp. Zoology Bull., vol. 12, No. 27, p. 41,1885. Idem, pp. 59-.

60 Phosphate Deposits Of Florida.

small percentage of phosphate of lime, but near the shore, in some places, the quantity is very considerable. Sharpies, who analyzed the ooze of the Gulf Stream, found —

Carbonate of lime 85. 62

Carbonate of magnesium 4. 26

Silica 1.32

Alumina 20

Oxide of iron 31

Phosphate of lime 18

Loss on ignition 8. 15

In certain concretions found by the Blake in the Florida Strait, and by the Challenger in various parts of the world near land, the quantity of phosphate of lime is very much greater than in the deposits. These concretions appear always to be associated in an intimate way with organisms.

In 125 &Lthoms southwest of Land Key, Fla., a fragment of bone waa obtained several centimeters in diameter. It was of a dirty brown color, of great hardness, and had a conchoidal fracture. A microscopic examination of thin sections showed that the bone strudture was perfectly preserved.

The following is the result of an analysis of this specimen by M. Klement:

Phosphoric acid (PjO) 33. 42

Carbonic acid (CO2) 5.80

Sulphuric acid (SO3) 2. 74

Fluorine L21

Lime(CaO) 5L90

Magnesia (MgO) 70

Iron and alumina 1. 56

Insoluble residue 21

Loss on ignition 2. 16

Oxygen corresponding to fluorine — . 51

There were also traces of silica and chlorine.

Atomic ratios.

Pa 1,417

Co2 - 264

So3 69

F 64

CaO 1,8531

MgO 35/

At the same place and depth there was a concretion of a brown color consisting of an aggregation of calcareous organisms cemented by a brownish-yellow matter, often showing concentric rings after the manner of agate. This yellowish-brown matter is isotropic; between crossed nicols only the calcite and the shells of the Foraminifera brighten up; the calcite lies crystallized in the interior of the Foraminifera. In treating the brown or yellow parts under the microscope with molybdate of ammo- nium and nitric acid, there is an abundant yellow precipitate characteristic of phos- phoric acid.

At other stations small phosphatic concretions were also obtained by the Blakey all more or less resembling those described above. There are difficulties in under-

Origin And Age Of The Phosphates. 61

standing how phosphate of lime and carbonate of lime are dex)osited at the bottom of the sea, yet there is no doubt that such a deposition does take place under some special circumstances. Their solution is, however, an almost universal phenomenon in the ocean.

All the phosphate nodules described by Sir John Murray were obtained at a depth of 125 fathoms or more, and many and possibly all of the nodules of the Alum Bluff formation were formed in much shallower water. Concerning the depth of water in Apalachicola time, Vaughan says:

The Plateau in early Apalachicolan time had practically the same outline aa at present; the depth of water north of Tampa was probably in no place over 100 feet. Coral reefs were present in southern Georgia, across the base of the present peninsula, and around Tampa; the temperature was tropical, the minimum for the year being at least aa high as F.; the main movement of the ocean water was from the Tropics; the sediments consisted to a lesser degree of organic debris and were prodominantly of terrigenous constituents.

It is doubtful whether the depth of water where the Alum Bluff deposits accumulated was greater than in the area around Tampa, and the character of the animal life and the aggregation of the ani- mal remains indicate that it may have been less than 50 feet. Prob- ably the conditions at that time over th;s part of the Florida Plateau were in some respects like those now existing between the Florida Keys and the mainland, for the Alum Bluff formation was deposited some distance from rivers bearing abundant sediments and the conditions were especially favorable to the existence of numerous marine animals. The possibility that phosphatic nodules may have accumulated rapidly should not be overlooked, because the shallow waters, having a high temperature, furnished conditions especially favorable to the development of marine life.

Phosphate nodules similar to those of the Alum Bluff formation were found in material obtained from the sea bottom by the Chal- leriger, and they were especially numerous near the border of the continent at places where large quantities of fresh water entered the ocean or where ocean currents of different temperatures met. Thus submarine phosphatic nodules were most abundant in the Atlantic Ocean off the eastern coast of North America and in the Pacific Ocean off Cape of Good Hope.

The similarity of the phosphate of the Alum Bluff formation to the nodules found in marine deposits off the continental shelf point to a similar mode of origin, and there is little doubt that the nodules of the Alum Bluff formation are marine phosphates. The arrangement of the phosphate nodules of Florida in layers of limestone and clay

I Report on the specimens of bottom deposits: Harvard Coll. Mus. Comp. Zoology Bull., vol. 12, No. 27, pp. 52-53, 1885.

Vaughan, T. W., A contribution to the geologic history of the Floridian Plateau: Carnegie Inst. Washington Pub. 133, p. 182, 1910.

Murray, Sir John, Deep-sea deposits: Report on the scientlflc results of the voyage of H. M. S. ChaU lenger, pp. 391-400, Ixmdon, 1891.

62 Phosphate Deposits Op Florida.

interbedded with barren clay indicates periodic accumulation. The many alternations of beds of clay containing phosphate nodules with beds of clay barren of nodules in the well at Christina show that there were many abrupt changes in conditions. That there was sudden destruction of a large number of animals is not clearly shown, for the same results might be obtained if the phosphate layers accumulated slowly enough to permit the formation of phosphate nodules and the barren clays were deposited too rapidly to allow such material to accumulate. In any event, if the animals were not destroyed by the conditions that resulted from an abrupt influx of sediment-laden water they were doubtless forced to abandon, for the time, their old habitat and to seek a new location where conditions for life were more favorable.

The area of the Alum Bluff formation is remote from points where large streams enter the sea and shows no signs of volcaj:iism or of other source of gases inimical to animal life, so it is necessary to seek some other explanation of the conditions that were at intervals un- favorable to the existence of animals. The geologic history of the region during Apalachicola time furnishes a clue to the conditions resulting in the deposition of the phosphate. At the beginning of this epoch the peninsula of Florida was reduced to an island separated from the mainland by the Suwannee Strait. Somewhat later the entire peninsula was submerged. This submergence was followed by sUght emergence of the central part of the peninsula, but in the meantime the Suwannee Strait was rapidly' being filled with sediment. When the Alum Bluff formation was laid down the strait may have been so much filled that the passage of water through it was at times partly or wholly obstructed. The conditions may have been such that a sUght change in level would have at times permitted the southward- moving cold current to pass through the Suwannee Strait, whereas at other times it was excluded. This current, sweeping across the area where clay and sand were being deposited, would bring with it terrigenous sediment, which would be deposited in the quiet waters of the Gulf coast, and frequent changes would produce the alternating layers of limestone and clays containing phosphate. The influx of mud would of itself have been sufficient to destroy some animals and to cause others to migrate to places where conditions were more favorable to their existence. Probably the difference in the tern- perature of the waters on the two sides of the peninsula was an addi- tional factor in the formation of the phosphates. It was at about this time that the tropical Oligocene faunas were replaced by the colder water Miocene faunas, and the physical changes that produced the faunal differences may have been begun during the closing stage of the deposition of the upper portion of the Ohgocene system. Thus it is thought that by a wholesale destruction of animal life, differences

Origin And Age Of The Phosphates. 63

in temperature may have played a part in the origin of the phosphates of the Apalachicola group, though such changes of temperature are not believed to have been essential to their formation.

Source Of The Phosphoric Acid.

In discussmg the origin of marine phosphates, Murray* says the phosphate was first extracted from sea water by living organisms, and on their death was dissolved and redeposited. The chemical reactions causing the precipitation of the phosphoric acid as calcium phosphate and the arrangement of the material in nodular form is not fully understood. Murray continues:

In that pulp fonned by the calcareous and siliceous organic envelopes, by the fragments of rocks and minerals reduced to the state of muddy matter, and by albu- minoid and other matters derived from higher organisms, the phosphates are rearranged, with the result that phosphate of lime in a nodular form is in some places found in considerable abundance. It may be supposed that this phosphatic matter, dissolved in the sea water impregnating the mud, is endowed with the properties of colloidal bodies, for we know that phosphate of lime presents incontestable analogies with certain colloids, for example, with hydrated silica. By admitting that phosphate of lime can effect this colloidal state, it is sufficient that a center of concretion should arise to initiate precipitation, and the nucleus once formed would subsequently enlarge by successive additions.*

Many substances may have played, with respect to the phosphate, the r61e of center of attraction. It may have originated in the first instance, as we have shown, in the filling up of the hollow spaces of a Globigerina shell; afterwards it may be depos- ited around this shell and agglutinate the surrounding portions of the deposit into a more or less compact mass. The organic remains on the bottom of the sea often retain for a long time some of their sarcodic substance, and we are inclined to think that this exerciser upon the phosphate an attraction which might be considered as a feeble echo of that exercised by living matter. This view might be supported by recalling the frequent incrustations of phosphate and its concretionary development upon the remains of plants and animals; at the same time it must be pointed out that phosphate of lime is sometimes formed around inert matters to which no affinity would appear to carry it. A solid body of any kind appears to serve as a nucleus, though phos- phatic nodules are by preference formed around organic centers, but whatever the nature of the nucleus, once the first layer of the concretionary substance is deposited it no longer remains inert, acting in its turn as a center of attraction and grouping round it, just as the solvents furnish material, all the molecules of the same nature which are found >vithin its radius of attraction.

The phosphates of the Alum Bluff formation are similar to the phosphatic nodules found by Sir John Murray' on the island of Malta. In both deposits the phosphates are in the form of granules and nodules, the nodules including portions of more or less altered

1 Report on the specimens of bottom deposits: Harvard Coll. Mas. Comp. Zoology Bull., vol. 12, No. 27 pp. 62-53, 1885.

The phosphate of lime may be held to be directly derived from the products of decaying bones of dead animais, upon which carbonic acid exerts a powerful solvent action. A t the same time the organic nitrog- enous matter of the bones is decomposed into ammoniacal salts, which would readily dissolve in water containing free carbonic acid and form a solution exceedingly prone to redeposit the phosphate of lime held in solution on any nucleus or in any cavities or shells.

The Maltese Islands, with special reference to their geological structure: Scottish Geog. Mag., vol. 6, pp. 449-488,1890.

64 Phosphate Deposits Of Flokida.

country rock. The phosphate nodules of Malta are aggregated in some beds but in others they form extensive layers of nodules. The great accumulation of phosphatic nodules at certain horizons are attributed by Sir John Murray to disturbances —

either in the neighboring continent, or in the ocean, or both. The emiasion of gaaes from submarine volcanoes, or an abnormal outflow of river water from the land fre- quently kills laige numbers of pelagic creatures, and their dead bodies may at such times form a vast layer on the bottom. The phosphate of ammonia thus arising would, in the deposits in process of formation, be decomposed in the presence of car- bonate of lime, giving rise to phosphate of lime and alkaline carbonates. The former, being insoluble, woul accumulate by pseudomorphism and mechanically in nodular form in the deposits accumulating on the sea floor.

Animal life was abundant while the beds contaroing the phosphates of Malta were deposited, for many fossils are found in those beds. Among these fossils are numerous sharks' teeth, which, like those associated with the marine-phosphate nodules, have been well pre- served by having their softer portions phosphatized. These phos- phatized teeth present a striking contrast to the many sharks' teeth dredged from the bottom of the deep sea, where phosphate nodules are rare, for these imphosphatized teeth are represented only by the outer shell of dentine, their more soluble parts having been removed by the corrosive action of the salt water.

The phosphoric acid of the Alum Bluff deposits was doubtless derived from remains of animals that extracted it from the sea water or that fed upon plants having power to obtain phosphoric acid from the same source. These plants may have supplied some phosphate directly to the deposits, though there is an absence of evidence on this point, but the abundant animal fossils show clearly that the animals were very numerous. The most prominent remains of organisms associated with the phosphate nodules are the shells of marine pelecypods and gastropods that inhabited shallow water. Attached to some of the shells are barnacles, and the whole deposit is aggregated in such a way as to indicate wave action. The fossils are so abundant that they are found in small exposures at the bottom of nearly all the phosphate mines in the land-pebble phos- phate region.

Sharks' teeth have been observed at many points, but they aro much more abundant in the overlying beds, which were derived largely from the Alum Bluff by weathering and erosion. Nearly all the teeth found in the ''bedrock" (Alum Bluff formation) are well preserved, showing no trace of corrosion by the water in which they were deposited. Bones of large animals are occasionally found and they also show no evidence of corrosion, though many of them have been broken.

1 The Maltese Islands, with special reference to their geological structure: Scottish Geog. Mag., vol. 6, p. 481, 1890.

Origin And Age Of The Phosphates. 66

Phosphate Of Bone Valley Obavel (Land-Pebble

The Bone Valley gravel is apparently of secondary origin, though some phosphatic material may have been added to it during its deposition. The source of the phosphate was the subjacent bedrock, as is shown by the facts that some of the phosphate pebbles are roimded nodules of phosphate derived from the underlying fonna- tion, having been merely reworked from the phosphatic layers, and that other pebbles are eroded and rounded fragments of the phos- phatized limestone. Many of these fragments still retain the texture of the original limestone, which contains small granules and pebbles of phosphate, and though a few of them are slightly calcareous, many of them have been entirely altered to phosphate.

The imoven surface of the Alima Bluff formation and the marked change from fine clays, containing small phosphate pebbles inter- bedded with limestones, to the coarser, more sandy conglomerates of the Bone Valley gravel (see PI. XVI, A) indicate a pronounced difference in the conditions under which these two formations were deposited and show that the period in which the Bone Valley gravel was laid down was preceded by a period in which there was con- siderable weathering and erosion of the older formation. During this interval a large amount of gravel, sand, and clay must have accumulated on the surface as a product of the weathering of the Alum Bluff formation and, with the incursion of the sea, with which the deposition of the Bone Valley gravel began, this material was eroded, roughly assorted, and redeposited in its present position. The proportion of phosphate pebbles in the Alum Bluff formation varies from place to place and different layers of the formation are near the surface at different points. Consequently the richness of the residual material in phosphate nodules and gravel was not uniform. In the process of redeposition the phosphate pebbles may have been at some places concentrated, whereas at other places they were more or less distributed, this difference accounting for the present varia- tions in the thickness and character of the phosphate-bearing part of the Bone Valley gravel.

The abundance of animal remains in the phosphate deposits sug- gests that some of the pebbles may represent original phosphatic nodules of organic origin that were deposited while the Bone Valley gravel was accumulating. Some of the pebbles appear to have been formed by the union of two or more smaller ones, and many of them contain minute phosphatic granules embedded in a matrix of phos- phate, but the phosphate nodules of the underlying formation have the same characteristics. Considerable attention was devoted to the pebbles of phosphate, as it was beheved that the original granules and small pebbles might be ooUtic. None of the thin sections pre- 36816°— Bull. 604—15 5

66 Phosphate Deposits Op Flobida.

pared, however, showed any evidence of oolitic texture, but some of them showed variations in density. The texture of the pebbles examined indicated that they were in part the result of phosphatiza- tion of the limestone of the Alum Bluff formation and in part the result of accretions of phosphatic material. Partly rounded or angular grains of quartz sand are common in the phosphate pebbles and usually show a tendency to accumulate or segregate, but they appear to show no uniform arrangement, for in one pebble these grains may be aggregated near the center, whereas in another they lie near the surface. Many fragments of bone are found in the Bone Valley gravel and these are, of course, phosphatic, but they form so small a proportion of the whole deposit that they are not conuner- cially important.

The Bone Valley gravel consists of a conglomerate of varying coarseness embedded in a matrix of sand or clay. At some localities the lower part of the phosphate is composed of blue to olive-green clay containing many dark-colored granules and small nodules of phosphate. At some places this clay forms the upper member of the Alum BluflF formation, but at others it has been eroded and redeposited in the lower part of the Bone Valley gravel. Above this fine material lies a varying thickness of the coarse sandy conglom- erate that is characteristic of the formation. These two materials show the difference in the conditions of deposition, ranging from sedimentation in quiet water to deposition of coarser beds whose texture varied under the influence of waves and shifting currents. Throughout the region there is frequent alternation of coarse and fine material, and though many layers have considerable horizontal extent, others are of lenticular shape. The general character and arrangement of the gravels and the frequent alternation of coarse and fine material showing gentle undulations, as represented in Plate XVI, B, indicates deposition in shallow water, and the pres- ence of fossils of marine animals shows that the material is of marine origin.

Topographic position. — The situation of the river-pebble phosphate points unmistakably to its fluviatile origin. The deposits lie beneath the flood plains and terrac of streams, where they form bars and irregular beds in the ancient stream channels. There is no question that they have been deposited in their present positions at times of flood, when the swollen streams were able to transport coarse material.

Source of phosphite. — In southern Florida the river-pebble phos- phate was largely eroded from the Bone Valley gravel, though some part of it may have been derived from the phosphatic nodules of the

A, Contact Of A

Containjng Frag-

Origin And Age Of The Phosphates. 67

Alum Bluff formation ("bedrock'). In northern Florida some of the river pebbles appear to have been nodules similar in structure to those of the Alum Bliiff , but in the absence of good specimens from the rivers of southern Florida it can only be surmised that similar pebbles exist there. The existence of such nodules near the northern end of the State is of unusual interest because they indicate the presence in that area of a formation similar to the ''bedrock" of the southern end of the peninsula.

According to Sellards/ the phosphates on Black Creek and other tributaries entering St. Johns River were derived from a phosphatic bed in the northern part of the peninsula. The exposure described by him is about 3 miles southeast of Brooker, where a phosphate bed underlies a marl containing Miocene fossils. A recent visit to this locality disclosed the fact that the phosphate consisted of a marl containing nodules similar to those found in the Alum Bluff forma- tion C'bedrock") of the pebble-phosphate region. Doubtless the erosion of rock phosphate has resulted in the formation of river- pebble deposits in some localities, but as the rock-phosphate region is largely drained underground tlus process has not been active in recent geologic time.

Organic remains collected from the beds by Sellards were assigned by him to two groups — those derived from the original rock and those incorporated with the phosphates during redeposition. The most common fossils belonging to the original rock are invertebrate remains derived from the beds of the Vicksburg group, with which are associated at many places shark teeth and fragments of bones from the same beds. The fossils incorporated with the redeposited phosphates are in part residual and in part contemporaneous. Sel- lards gives the following localities:

Of the foasils that are accepted an contemporaneous with the phosphate formation the best authenticated is a species of mastodon, probably M. Jhridanus. This mas- todon has been obtained in the hard-rock phosphate section from the following mines: T. A. Thompson, Neals, Alachua County; Button Phosphate Co., plant No. 22, Juliette, Marion County; Cullen River Mine, Dunnellon, and Dunnellon Phosphate Co., plant No. 5, Hernando, Citrus County. That the mastodon is actually embedded in the phosphate-bearing formation is not only vouched for by the miners who have personally taken specimens from the pits but is evident from the specimens them- selves, some of which have the gray phosphatic sands of the phosphate formation adher- ing to them. Associated with the mastodon is found the small three- toed horse Hip- parion. The remains of the horse have been obtained only from the picker belt, but notwithstanding the fact that they have gone through the washer some of the teeth still have bits of the phosphate matrix clinging to them. The horse remains

1 Sellanls, E. H., HJneral industries: Florida Geol. Surrey Second Ann. Rept., p. 240, 1909. s Sellards, E. H., Origin of the hard-rock jdiosphate deposits of Florida: Florida Oeol Survey Fifth Ann. Kept., pp. 5668, 1913.

68 Phosphate Deposits Of Florida.

have been obtained from the following mines: Franklin Phosphate Co. mine No. 2, Newberry, and T. A. Thompson, Neals, both in Alachua County; Dunnellon Phos- phate Co., plant No. 6, Dunnellon, Marion County, and Dunnellon Phosphate Co., plant No. 5, Hernando, Citrus County. A number of other fossils have been obtained, which remain to be determined. Among these are teeth of an early camel from Dunnellon Phosphate Co., plant No. 5, Hernando, Citrus County, and Cullen River mine, Dunnellon.

Concerning the vertebrate fossils figured by Sellards, Mr. J. W. Gidley, of the United States National Museum, has furnished the following note:

In answer to your inquiry regarding the mammal remains figured in the Fifth Annual Report of the Florida Geological Survey, I can only say that the horse teeth figured on plate 5 represent two genera and are apparently referable to Leidy 's species, the two on the left and the toe bone being Hipparion pUcatile the others EquuBfra" emus. The status of neither of these species is well established, they being known only from teeth and isolated bones, hence their value as horizon markers is limited. The Hipparion species indicates a Miocene or possibly a Pliocene age, while the Equus indicates a Pleistocene phase. Yet there is no proof that these species may not have been contemporaneous, the former being a later survival of Hipparion than is recorded in the fossil-bearing deposits of the West, or, possibly but not so likely, the latter may be an earlier representative of Equus than is known in the fossil beds of the West.

Like the horses of the Coastal Plain deposits, the mastodons also are known only from teeth and fragments, representing probably three or foiu" species, and the material, to make it of any great value in determining horizons, should receive much more careful study than has ever been given it.

The suggestion made by Eldridge that the phosphate may have been redeposited when the peninsula was last submerged applies to only a few deposits. The latest submergence occurred during the Pleistocene epoch, and the major part of the deposits of that epoch is sand, but in a few places phosphate was eroded, assorted, and redeposited.

Some fossils collected at the mines along Withlacoochee River were identified by Gidley as Pleistocene, this determination indicating more or less redeposition at that locality since the beginning of the Pleistocene epoch. Doubtless the material in the Pleistocene ter- races was more or less reworked during their formation, but it is not easy to determine the amount of redeposition in places where there are no characteristic fossils.

Phosphates Of Apalachicola Gboxtp.

The phosphates occurring in the Alum Bluff formation bedrock") are believed to be an original constituent of the formation, and their age, as indicated by the accompanying fossils, is about the same as

1 Eldridge, G. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Mln. Eng. Trans., vol. 21, pp. 217-218, 1892.

Composition Of The Phosphates. 69

that of the Oak Grove sand member of the Alum Bluflf formation of Santa Rosa Cotmty. This member lies near the top of the Alum Bluff formation, a fact that correlates the phosphates of the Apa- lachicola group of the southern part of the peninsula with the upper- most part of the Oligocene series. It is not yet possible to decide the relations of some of the Apalachicola phosphates in other parts of Florida to those in the Alum Bluff formation, though at several places there are phosphatio pebbles eroded from the Vicksburg de- posits and at other localities there are nodules similar to those found in the Alum Bluff formation.

Bone Vauley Gravel (Land-Pebble Phosphate).

The age of the Bone Valley gravel has been discussed in connection with the geology. (See pp. 21-22.) To sum up, it is clear that these phosphate beds are somewhat younger than the underlying Alum Bhiff formation, from which they are separated by a distinct uncon- formity. The abundant animal remains, except those derived from the underlying formation by erosion and redeposition, are largely vertebrate and are not sufficiently distinctive to differentiate between uppermost Miocene and lowermost Pliocene, though they are prob- ably Miocene. The altitude of the beds accords more nearly with that of the marine Miocene than with the marine PUocene of the peninsula of Florida, and in the absence of marked deformation this fact is thought to strengthen the evidence of the Miocene age of the phosphate.

The deposits of river-pebble phosphate form parts of extensive accumulations of detritus in the valleys of some of the streams flow- ing through regions containing other types of phosphate. The ero- sion of the stream valleys began about the close of the Pliocene epoch and the deposition of the terraces occmred during late Pleis- tocene time. Those phosphates that underlie the terraces may there- fore be correlated with the younger Pleistocene. After the Pleisto- cene terraces were formed considerable phosphate was deposited in the flood plains and bars along the present streams. These phosphates are Recent and their deposition is still in progress, though the rate of their accumulation is very slow.

Composition Of The Phosphates.

Couuercial Requibehents.

In considering the composition of phosphate for commercial uses only a few substances need to be taken into account. These are insoluble matter O&rgely sand), iron oxide, alumina, carbonic

70 Phosphate Deposits Of Florida.

acid, aQc[ phosphoric acid. Of these substances the phosphoric acid only is valuable, the others being more or less deleterious or suggesting the presence of objectionable compounds.

The least objectionable of these substances is the sand or insoluble matter, which is unimportant except that it adds a certain amount of weight, thus diminishing the proportion of valuable material in the phosphate. The carbonic .acid is not in itself important, but it may indicate the presence of calcite or other carbonates. In the process of making superphosphates sulphuric acid combines with the bases of these carbonates, so that a larger amount of acid is required to produce superphosphates from a rock that contains carbonates than from one that contains no carbonates. Both the iron and the aluminum oxide are troublesome, because in the process used in making superphosphates they cause some of the phosphates to become insoluble, and if they are present in considerable quantities they greatly retard the drying of the superphosphates.

The contracts made for the purchase or sale of large quantities of phosphate rock prescribe certain standards of purity or enrich- ment, specifying a minimum percentage of phosphoric acid, usually estimated as tricalcixmi phosphate (bone phosphate of lime), and a maximum percentage of aluminum and iron, estimated as oxides. Rock phosphate, for example, is sold under a fixed standard or guaranty of at least 77 per cent tricalcium phosphate and not more than 3 per cent of both iron and aluminum oxides. If the rock does not conform to these requirements it must be mixed with material of higher grade imtil it reaches the standard, otherwise it may be rejected; or, if accepted, its price may be reduced in propor- tion to the amount the analysis shows the rock to be below the standard agreed upon. No fixed standards have been estabUshed for pebble phosphate and presxmiably each contract for the sale of rock is made in accordance with standards fixed by agreement becwtoen buyer and seller.

Rock Phosphate.

Owing to the variability in the composition of the Florida phos- phates composite samples of large quantities of rock give the most reUable information concerning values. The accompanying table gives analyses of rock from different parts of the rock-phosphate region and of plate rock from the area east of Ocala. No. 1, from the Newberry district, shows sUghtly less tricalcium phosphate than No. 2, from the southern end of the rock-phosphate region; but the conditions might be reversed by other analyses. No anidyses have been given of composite samples taken at Dunnellon, but analyses of some composite samples obtained in that vicinity give over 82 per cent tricalcium phosphate and only small quantities

Composition Of The Phosphates.

of oxides of iron and aluminum. However, the average grade may not be higher than that of the phosphate mined some distance north and south of Dimnellon, a fact illustrated by three analyses given by Jumeau,* showing, respectively, 78.90, 78.42, and 81.06 per cent tricalcium phosphate and 3.09, 2.56, and 2.96 per cent oxides of iron and aluminum.

Analytes of phosphate Florida,

Insoluble (SlOi)

Oxide of ircnCFeiOs)

AlumJna (A1|0)

Calcium oxide (paO )

Carboiiioacid(COj)

PhoBphorio acid (PsOft)

Tricalcium pliospbate (bone phosphate of lime) (CatPiOt).

1. From the Newberry district. Analyted by J. O. Fairchlld.

2. From the southern end of the rock-phosphate reeion.

3. Composite sample from several prospect holes in SW. i SB. see. 7, T. 15 S., R. 23 E. Tallahassee meridian.

4. Composite sample from several prospect holes In BE. SW. i sec. 19, T. 15 8., R. 23 £. TaUahasaee meridian.

5. Composite sample from several prospect holes In SW. BE. i sec. 10, T. 15 B., R. 28 B. Tallahassee meridian.

3, 4, and 5 analyzed by H. Henog, Jr.

The samples taken east of Ocala were obtained from prospect holes. To illustrate the variation in grade samples of bormgs taken from holes in the NW. NW. sec. 30, T. 15 S., R. 23 E., Talla- hassee meridian, were analyzed by Mr. W. H. Waggaman, of the United States Bureau of Soils. One sample contained 79.3 per cent tricalcium phosphate; another contained only 75.3 per cent. Still greater differences were noted in samples taken from only one or two prospect holes. Samples 4 and 5 are composites from several prospect holes on the same phosphate deposit on adjoining tracts of land, and though they contain about the same percentages of tri- calcimn phosphate they show considerable variation in the percent- ages of oxides of iron and aluminum. Sample 3 was taken from a deposit in which considerable calcium carbonate was mixed with the phosphate. Differences of this sort are found in all parts of the rock- phosphate region, and some are much greater than those shown by these analyses.

A large number of analyses of various types of Florida phosphates have been made. The following analyses, republished from Survey Bulletin 491,* show the percentages of a large number of substances found in the rock phosphate and the great difference in the compo- sition of different samples.

1 Jumeau, L. P., Le phosphate de ohaux et les exploitations aux £tets-UnJs en 1905, p. 138, Paris, 1905. Clarke, F. W., The date of geochemistry: U. S. Qed. Survey Bull. 491, p. 508, 1911.

Phosphate Deposits Of Florida,

Analyses of phosphate from Florida. [Analyses by George Steigo-.]

SlOs

TiO,

AlsOs

FeiOs

CaO

MgO

KsO

NajO

Co,

So,

F

H.OatlOJ*. IgnlUon

Trace.

Trace.

.Co

Less O,

Organic C.

Os. 65

None.

None.

33,37

.Co

loaso

ia63

2. Co

3a 35

23. £5

10a57

6. From near Sunnyside, Taylor County.

If 8. From LuravUle district, Suwannee County.

9. From Albion district, Levy County.

These analyses have an additional interest because the samples were obtained from localities where mining has been abandoned.

A table given by Eldridge and reprinted below shows the com- position of some different types of rock phosphate. As most of the analyses were made from small specimens they may not tiiily repre- sent the character of the rock of such types.

Chemical analyses of phosphates from Florida. [Analyses by T. M. Chatard.J

Lo8S(IT,O)atl05*C... Loss (n,0) at red beat.

Co,.

Insoluble residue Cin rci, IINOs). Insoluble residue (in HNO,)

(Al,Fe,)0,

A1,0, Fe,0,.

CaO..

MgO.

Pj06.

2.3:

If 2.191

2.2e[2.27

1 1 2.32)

.98f

46,

33.93]

10. Typical gray phosphate.

11. Mottled brown and white phosphate.

12. Mammillnry incrustition.

13. A fossliiferoas phosphate, containing cavities with sand.

X Eldridge, O. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., yoL 21, p. 225, 1893.

Oomposition Of Th£ Phosphates.

Chemical ancdyses of phosphates from Florida — Continued.

L08saiiO)atl05C... Loss (HsO) at red heat. COt.

Inaolublo residue (in IICl, HNOs) Insolublo residue (in HNOs)

(AljFeOOa

A1,0. FetOi.

CaO..

MgO.

PfOs.

0.08

/ 38.40Uo

/ 62.01U 62.02r

2.2o

2.r,i

l.CJ

14. lYhlte, coarsely Umlnated phosphate, with clay in cavities. 16. Gray variety of No. 80, typical.

16. Typical laminated phosphate from same locality as 98.

17. A granular-looking phosphate, light gray.

18. The ooaiser portion of 1(10, after sejMration on a 20'mesh sieye.

In exploiting a deposit of phosphate composed of fragments of different sizes, the composition of material of the several grades of fineness is an important guide to the miner in determining how the material shall be separated. Several years ago studies were begun by Dr. Chatard to determine the quaUty of particles of various sizes. Of a sample of rock phosphate from Florida, screened dry (A in table), 64.62 per cent was left on a 20-mesh sieve. The remain- ing 35.38 per cent (B) of the sample was assorted by water in a Thoulet tube into four grades: Bj (coarsest), 12.06 per cent of original material; Bj (middle), 5.31 per cent; Bj (finest), 16.31 per cent; lost by remaining in suspension, 1.70 per cent. Dr. Chatard's analyses of the materials obtained by this method are given in the following table:

Analyses of particles of phosphates of different sizes {No. 19).

B,.

Insoluble

(AliFei)O,

PaOft

CatPiOi

Total sample.

A.

B.

Bi.

From these analyses Dr. Chatard concluded that 82 per cent of the original sample comprised in portions A, B, and B, contained the high-grade rock, and that the finest material, B,, contained too much ferric oxide and alumina to be marketable.

1 Chatard, T. M., Phosphate chemistry as it concerns the miner: Am. Inst. Min. Eng. Trans., vol. 21, 1902-, pp. 160-175. s Op. cit., p. 161

PHOSPHATE DEPOSITS OF FLORmA.

Dr. Chatard made similar experiments with a phosphatic sand rock from the Itchetucknee region in Florida. The results, shown in the table below, gave (A) 20.74 per cent of sample on a 20-mesh sieve. The use of the Thoulet tube on the remaining 79.26 per cent (B) of the sample gave Bj 37.83 per cent, B, 20.87 per cent, B, 17.75 per cent, and loss 2.81 per cent. The analyses of the materials of different grades given in the accompanying table show that this method of separation does not give satisfactory results where there is an intimate mixture of phosphate and clay.

Analyses o/phosphcUe and rock from Florida {No, SO).

Bs.

Insoluble. (Al,Fe)0;

CatPioi!!

Total sample.

A.

B.

B,.

B,.

Unfortunately Dr. Chatard work was interrupted and he had no opportunity to carry it to completion, but the results he obtained indicated the practical value of his study.

A similar investigation was made by Waggaman,* who, however, used samples that had been burned. His results are given below. He says:

In some sections of the hard-rock region, where considerable phosphate of alumina occurs, the rock is screened after burning. It is claimed that this screening reduces the percentage of iron and alumina and raises the grade of the rock. In order to see if this would hold true under ordinary conditions where the deposit contained no abnormal amount of aluminum phosphate, the author collected samples both of medium-sized and of small fragments (not larger than a pea) from the same pile ot burned rock and analyzed them. The results are given in the table below.

Chemical analyses of samples of large and small pieces of hard-rock phosphate after burning.

Sam-

Location.

Description.

Analyses.

ple.

810,.

FejOa.

A1,0,.

CaCPOOi.

DanneUon

Nodular, hard , fairly large lumps. . . iSmnll fraents

1,16

It will be seen from inspection of this table that both the silica and the iron and alumina are higher in the sample of small fragments than in that composed of larger pieces. The difference in the quality of the two samples is not only due to the dis- integration of the aluminum phosphate but also to the fact that the larger pieces are sorted and many impure pieces thus eliminated.

1 Chatard, T. H., op. cit.

1 Waggaman, W. H., Areview of the phosphate fields of Florida: U. S. Dept. Agr. Bur. Soils Bull. 76, p. 12, 1011.

Composition Of The Phosphates.

Mr. Waggaman also made analyses of two types of rock to deter- mine the effect of burning, and his results are given below.*

Chemical analyses of samples of hard-rock phosphate before and after burning, [All the samples were dried in the laboratory at C. for at least four hours.]

Sample numi

iple loer.

23A

24A

Description.

Blue rock, hard, not burned . .

Blue rock, hard, burned

White roclc, hard, not burned White rock, hard, burned

Analysis.

PjOj.

Ca8(P04)i.

Waste From Bock Phosphate.

In the discussion of the methods of mining (pp. 89-98) mention is made of the material lost in preparing the phosphate for market. This waste is variable in composition and not many analyses of it were madC; so that it is impossible to determine accurately how much phosphoric acid is bemg thrown away. Most of the valuable material lost is soft phosphate of lime, though doubtless some phosphate of aluminum and iron is mixed with this phosphate.

Concerning soft phosphate Jumeau says that its cont<ent of tri- calcium phosphate ranges from 50 to 60 per cent, and that some pockets contain material yielding 65 per cent. Its content of iron and aluminum oxides, according to this author, range from 5 to 10 per cent and may rise above 15 per cent or fall below 3 per cent.

The following analysis given by Eldridge shows the composition of a sample of soft-clay phosphate.

Chemical analysis of typical soft-clay phosphate front Florida {No. tS).

[Analysis by T. M. Chatard.]

LoflB ( H2O ) a 1 105 C 0. 46

Loss (HO) at red heat 4.76

Co2 2.33

F

Insoluble residuufii (in HCl, HXO3). Insoluble residuum (in HNO3)

(Al2Fe2)03

Ai2O3

FejO,

CaO

f 7.931 I 7.78/

r 44. 051 t 44. 04/

MgO

2&

r 35. 281

I 35.11/

1 Waggaman, W. H., A review of the'phosphate fields of Florida: U. S. Dept. Agr. Dur. Soils Bull. 76, p. 12, mi. s Jumeau, L. P., Le phosphate de chaux et les exploitattons aux £tats-Unis en 1006, p. 147, Paris, lOOS. a Bldridge, O. H.| A preliminary sketch of the phosphates of Florida: Am. Inst. l£iii. Eng< Trani.i voL

9ii p. aaO| laM.

Phosphate Deposits Of Florida.

Waggaman estimates the amount of phosphoric acid lost in mining at twice the quantity saved. There is no question that some of this material might be utilized advantageously on soils devoted to general farming, and if a cheaper method of producing acid phosphate could be devised it might be possible to use much of this low-grade material. Analyses of waste materials are given by Waggaman, who says:

Samples taken from various parts of the "vraste pile differ greatly in composition, as considerable mechanical separation takes place when the stream of water carrying this detritus is discharged upon the waste heap, because the clay and soft phosphates being held in suspension longest are carried some distance, while the sand and hea\der particles are deposited more rapidly.

In order to get a better idea of its actual composition the author carefully washed some of the phosphatic detritus as it was brought from a prospect hole. The wash water and all material finer than 1 millimeter w?ro saved, and after evaporating the water the sample was thoroughly dried and mixed. The analyses of this material, together with some made by other chemists, are given below.

Chemical analyses of material washed atoay in preparing hard roch for the market.

Sam- ple

No.

Location.

Analyst.

Analysis.

SiOs.

AUOi.

FeiOi.

PjOs.

Ca,(PO0.

SW.}sec.30,T.15,R.23E.

Anthony

do...

Newberry. 5 id lies south- east o/Dunnellon.

W. H. Waggaman

P. Jumeau

Co. 10 /

do

In olBoe of Florida SUitc chemist.

::

In the process of sorting rock phosphate on the ''picking belt" considerable phosphatic material is rejected by inexperienced work- men and some is removed by skilled laborers, because it is not always possible to distinguish the good material from the poor. The fol- lowing analysis of refuse from the pioking belt was made by Wagga-

man:

Chemical analysis of a sample of material throvm from picking table.

Sam- ple No.

Location.

Description.

Analysis.

SiOt.

AljOs.

FosOs.

CaacPOOs.

Dunnellon...

Clay balls, limestone, etc

Phosphates Of The Alt7M Bltj7F Formation.

Few samples of phosphate from the Alum Bluff formation have been analyzed, though phosphatic nodules are abundant in some layers in both northern and southern Florida, being found at many

1 Waggaman, W. H., A ravtow of the phosphate fleldi of Florida: U. S. Dept. Agr. Bur. Soils Bull. 76> p. 14, 1911. Idem, p. 10.

Composition Of The Phosphates.

places in the ' bedrock ' ' of the pebble-phosphate region, on Sopchoppy River near Sopchoppy, and at other widely scattered localities. The following analyses by A. B. Howe are of samples of Alum Bluff rock from a quarry formerly operated near Hawthorn:

Analysis of first sample (No. SI).

Mean.

AljO,. FejOs CaC. MgO. HiO..

4(L70

(14.28)

46.78S

101.40, 101.445

The second specimen was like the first, porous and slightly yellow- ish in color, but it was softer, a circumstance due to the fact that it had been lately quarried. Its composition was as foUows:

Analysis of second sample {No. S2).

SiOs..

FetOs

CaO..

MgO.

NaiO.

KsO..

PfOi.

H,0.

Co,..

n.

6a 76

Mean.

6a73

In order to determine the composition of the ''bedrock'' analyses of samples were made in the laboratory of the United States Geolog- ical Survey. The results are given below, and they show some inter- esting peculiarities:

Sample No. 33 was obtained from a mine near Mulberry. This rock is a light-yellow limestone or dolomite containing many brown nod- ules of phosphate. Mr. J. G. FairchUd, who made the analyses, removed the phosphate nodules from the matrix and analyzed each separately. Because of the intimate mixture of the two portions of the rock complete separation was not possible, but the results indicate the general composition of the two constituents.

The matrix (No 33A) contained a little phosphate, probably in the form of minute granules, and the high percentage of magnesia present shows that the rock has very nearly the composition of a dolomite. The percentage of phosphate in the nodules (No. 33B) is relatively high, and magnesia is present in small quantities. These nodules have the same general characteristics as the ones described in the discussion

1 U. 8. Nat. Mus. Proc., vol. 6, pp. 47, 48, 1882.

Phosphate Deposits Of Florida.

of the phosphatesof the Alum Bluff formation ('bedrock'*), (pp. 33-35), and are doubtless nodules of marine origin. The presence of the mag- nesia in the phosphate nodules indicates that dolomitization was in progress during the process of the deposition of the phosphate and was marine. The presence of a much higher percentage of material insol- uble in nitric acid in the matrix than in the phosphate nodules proba- bly indicates that phosphatization was influenced by the composition of the rock, nodules forming where the limestone was relatively pure, though the sample had been subjected to the action of surface water and the matrix had doubtless been leached of a part of its soluble calcium carbonate, thus increasing the proportion of relatively insol- uble material, such as sand and magnesium carbonate, while the phosphate suffered little loss because it was much less soluble than the calcium carbonate.

Sample No. 34, a pebble phosphate from the central part of the region, is classed with limestone of the Alum Bluff formation, though the matrix is sandy. This sample contains less phosphate than No. iB and more magnesia and other relatively insoluble matter.

Sample No. 35 is a phosphatized portion of the "bedrock" at Chris- tina, in which considerable insoluble material represents the large percentage of impurities in the original limestone. In this sample phosphatization has been nearly complete and there is very little magnesia, but the limestone at this locality may contain less than that farther south. In any event there is no reason to suppose that the replacement of carbonic acid by phosphoric acid would be accom- panied by the removal of magnesia. The alteration of this rock had resulted in considerable increase in its contents of phosphoric acid but the change had not been complete, as is shown by the presence of some carbonic acid.

Analyses of Florida phosphate. [A]ialys6 by J. O. Fairchild, United States Geological Survey.]

Insoluble in HNOs. SiO (acid soluble).. (AbFei)O,

PtOft

COt

MnO

CaCOs (calculated). . CasPjOg (calculated) UgpOt (calculated) .

a 4.

&83

96w76

8&73

o Probably.

33. Bedrock from Prairie Pebble Phosphate Co.'s mine near Mulberrv: A, matrix; B, nodules,

34. Pebble phosphate from Alum Bluff formation.

35. Pbosphatic limestone from Alum Bluff formation at Christina,

Composition Of The Phosphates. 79

On page 81 there is given a partial analysis of a sample of the "bedrock/' taken at a locality a mile north of Bartow, which con- tained 75 per cent of calcium carbonate and only 5 per cent of tri- calcium phosphate. Thus the rock at that place is comparatively poor in phosphoric acid. It is remarkable, moreover, for its small contents (0.5 per cent) of iron oxide and alumina.

Iand-Febble Phosphate.

Though few analyses are available for pubUcation enough informa- tion has been gathered to indicate that the average content of tri- calcium phosphate in land-pebble phosphate ranges from about 65 to 75 per cent. The better grades of phosphate near the north end of the region may contain over 77 per cent tricalcium phosphate for some analyses show a content of over 80 per cent. The. average percentage of tricalcium phosphate declines toward the south, but there are so many local variations that this generaUzation will not apply to all places.

The accompanying analyses were made from composite samples of material taken from several prospect holes distributed with some degree of uniformity over 40-acre tracts of land. The tracts lie within a few miles of the north end of the region, and it is worthy of note that these two samples, which contained, respectively, 74.85 and 75.26 per cent of tricalcium phosphate and only 4.15 per cent and 2.91 per cent of aluminum and iron oxides, compare favorably with some of the lower grades of rock phosphate.

Analyses of wmples of phosphate taken from prospect holes at north end of phosphate

region of Florida,

[Dried at 212* Apr. 12, 1911, F. H. Herxog, jr., analyst.]

Sand(SI0,) 4.78 5.34

Iron oxide (FeiOs) . .r

Tricalcium phosphate (bone phosphate of lime) (CaPiOa) 74. 85 75. 26

38. From the SE. SW. sec. 19, T. 15 S., R. 23 E. Tallahassee Meridian. 37. From the SW. SE. sec. 19, T. 15 S., R. 23 £. Tallahassee Meridian.

The samples represented by the following analyses were taken from mines in the central part of the pebble-phosphate region, 38 being from the vicinity of Bartow. The exact locality at which the other sample was taken is somewhat uncertain.

Phosphate Deposits Of Flortoa.

Chemiocd anoLyHs of washed pebble phosphates Jrom Florida,

[Analyses by T. M. Chatard.]

Loss rH0) at 105* C

Loss (HfO) at red heat

COa

F

Insoluble residuum Cln HCI, HNOs)

Insoluble residuum (in HNO3)

A1,0,

FeiOs

CaO

MgO

PsOft

o Eldridi;e, O. H., A preliminary sketch of the phosphates of Florida: Am. Inst. MIn. Eng. Trans., toL 21, pp. 230-231, 1883.

Chatard examined some samples of pebble phosphate taken from a mine near Bartow to determine the best method of treating the product. A sample disintegrated in water was washed on a 20-mesh sieve, which retained 54.54 per cent of the original sample in the form of pebbles, the matrix, which had passed through the sieve, compris- ing the remaining 45.46 per cent. The analysis given below indicates that although a large percentage of th6 best material is held on a sieve of 20 meshes to the inch, some phosphate passes through. This loss might be avoided by using a sieve with smaller openings, but the grade of the material held by a finer screen would probably be lowered.

Analyses of pebble phosphate from a mine near Bartow.

No. 40, pebble.

Insoluble. (Al,Fei)08

PtOft

CatPiOs. . .

7&60

No. 41, matrix.

29. Go

In order to determine the relative values of pebbles of different colors, Waggaman ' made the analyses given below. He says:

In the table below are given the analyses of three different-colored samples. It will be noted that the black pebbles and white pebbles are richer in phosphoric acid than the brown or yellow. This same appears to be true in the hard-rock regiooB.

i Chatard, T. M., Am. Inst. Mln. Eng. Trans., vol. 21, pp. 164-165, 1893.

t Waggaman, W. II., A review of the phosphate fields of Florida: U. 8. Dept. Agr. Bur. Soils Bull. 76, p. 19, 1911.

Compositton Of The Phosphates.

Chemical ancdyses of samples of differentrcolored pebble phosphate from Mulberry Fla.

Sam- ple.

Location.

Mulberry

do...

do...

Description.

Small black pebbles. Small white pebbles . Small brown pebbles

Analyses.

Sio,.

AlsOt.

Ca,(P04)i.

The generalization made by Waggaman is doubtless subject to some exceptions, for the best rock varies in color at different places.

Differences in the grade of the phosphate in different layers have been noted in many of the mines. In some mines, in a vertical thick- ness of 10 or 12 feet, there may be variations of 4 or 5 per cent in the amount of tricalcium phosphate in the coarse and the fine material or in the light, porous pebbles and the hard, dense pebbles. The size of the material does not appear to indicate its grade, for in one mine the coarse material, in another the fine material, and in still another the medium-sized pebbles may be the high-grade rock. In addition to abrupt variations in the quality of the rock in a single vertical sec- tion, there are horizontal differences, which are so marked that within a distance of 50 feet the content of tricalcium phosphate may vary 4 or 5 per cent, and extreme variations of nearly 30 per cent have been noted.

A detailed section, supplied to Mdridge by Dr. Chazal, is given below:

Section 1 mile north of Bartow.

Feet.

Surface soil and sand 2

Phosphate gravel containing a few pebbles. of sand, the whole em- bedded in a matrix of ferruginous sand. The phosphate pebbles are nearly all white, but are coated with a brown stain. These pebbles comprise 33 x>er cent of the whole bed and contain 70 per cent tricalcium phosphate and 5 per cent oxides of iron and aluminum 1-2

Clay containing some layers of sand near the top; phosphate pebbles 33 per cent of the whole, containing 64 to 72 per cent tricalcium phosphate and 4.5 to 6 per cent of oxides of iron and aluminum. The clay in this layer gave considerable trouble in washing because of its tendency to form balls 6

Clay containing 10 per cent of phosphate pebbles, which showed on analysis 72 per cent tricalcium phosphate and 4.5 per cent oxides of iron and aluminum 6

**Bone containing 30 per cent phosphate pebbles, which on analysis showed 72 per cent tricalcium phosphate and 4.5 per cent oxides of iron and aluminum 3

"Bedrock, " consisting of hard marl and limestone, which on anal- ysis showed 75 percent calcium carbonate, 5 percent tricalcium phosphate, and 0.5 per cent oxides of iron and aluminum.

85816**— Bull. 604—15 6

82 Phosphate Deposits Op Flobida.

Waste From Land-Pebblb Phosphate.

The amount of phosphoric acid lost in preparing the land-j>ebble phosphate for market has not been determined, but it probabljr does not exceed one-half the quantity mined. Few analyses are available to show the composition of the matrix that is rejected in mining. The analysis ahady quoted (p. 80) shows the composition of material passing a 20-mesh sieve, but a somewhat coarser screen is employed in mining. The following analysis given by Eldridge is probably open to the objection that it may not be representative of this typo of material because the sample was small. However, if instead of taking the matrix from a single small sample the chemist had been furnished a composite sample from many tons of such material, the average composition at the locality at which the sample was taken might have been determined.

Chemical analyses of matrix of land-pebble phosphate (No. 45).

[Analysis by T. M. Chatard.]

Lo88 (HaO) at 105° C 3.34

Lo88 (HjO) at red heat 6. 88

COj 82

F 88

iDfloluble residuum (in HCl, HNO,) 0. 00

Insoluble residuum (in HNO3) 49.78

Aia 6.85

FeaOs 1.05

CaoKl 15.92

°' [ .37J

PaOJlHl 13.58

tl3.6ir

In washing pebble phosphate a large number of clay balls are screened out and carried to the waste heap. The day that makes up the bulk of these balls contains some pebbles of phosphate, most of which are similar to the pebbles saved in mining. In addition to the phosphate lost in balls removed by screening some material is lost from "picking belts" at a few mines. The composition of these two types of waste, as determined by Waggaman,* is given in the table below.

An analysis was made of the material having a diameter greater than inches dis- carded before the material containing the phosphate goes through the washing process. The composition of a sample thrown from the picking table at one of the plants was also determined. These analyses are given in the following table:

1 Eldridge, G. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., vol, 21, p. 231, 1893.

Waggaman, W. H., A review of the phosphate fields of Florida: U, 8. Dept. Agr. Bur, Soils BulL76; p. 22, 1911.

Composition Of The Phosphates.

Cliemical analyses of waste or discarded material at pfiosphate mines in Florida.

Sam- ple No.

Description.

Analyses.

BiOs.

Aw,.

FetOj.

Cat(P04)t.

Clay balls, inches in diameter, containing phos- phate pebbles from discard

5a 58

Mftterlaiirom picWiu? tabl . .

Ph08Phatic Mabl.

The phosphatic marl in the overburden of the pebble-phosphate

region is relatively unimportant commercially, being mined at Fort

Meade only, and there m a primitive fashion. The product of this

mine is said to be high-grade phosphate rock, but no analyses are

available for publication. A sample from the overburden of one .of

the pebble-phosphate mines near Fort Meade was submitted to Mr.

Faircliild and the result of his analysis is given below. The marl

contained a large amount of fine sand, the presence of which accoimts,

in part, for the high percentage of material insoluble in nitric acid

(HNOj). There was also a relatively high percentage of iron oxide

(FeOs) and alumina and iron (AljOj), and this fact, together with the

small percentages of Ume (CaO) and magnesia (MgO), suggests that

the phosphoric acid was probably combined with the iron and alumina.

Analysis of phosphatic marl (No. 4S).

[Analyzed in the laboratory of the V. S. Geoloiical Survey by J. G. FairchUd.]

Insoluble in HNO, 70. 74

SiOa (acid soluble) 10

(Al2Fe2)03 1L84

CaO 78

MgO 11

Pa 10.06

Co2 09

MnO Trace.

Biveb-Pebblb Phosphate.

River-pebble phosphate is not now mined, and there is no indi- cation that its exploitation will be renewed, but it was the first rock marketed from Florida, and for a number of years its recovery was a profitable industry. The quality of the phosphate was lower than that obtained from the land-pebble and rock-phosphate mines, the proportion of phosphoric acid usually falling below 30 per cent, which is equivalent to about 65.5 per cent trioalcium phosphate. The general range in composition for this type of rock was from 55 to 65 per cent tricalcium phosphate, though in some places the rock

Phosphate Deposits Of Florida.

aver

yx'aged less than 55 per cent and a few analyses gave results some- what higher than 65 per cent. The following analyses of this type of rock are given by Eldridge:

Chemical analyses of river-pebble phosphates from Florida.

[Analyses by T. M. Chatard.]

Loss (HtO) at 1(W C. . Loss (H3O) at red heat CO,

F

Insoluble residuum (In HCL HNOj)

Insoluble residuum (In HNOs)

Fe,08

CaO

MgO PsO..

Niunbers of samples.

r 2.451

49. Peace River; dried pebble, from a bin,

50. Caloosahatchee River; picked pebbles from a lighter load.

51. Black Creek; air-dried pebble.

MrNTERALOGY.

The phosphate deposits of Florida consist of more or less earthy phosphorites whose physical characteristics vary, depending roughly on the proportion of their content of calcium phosphate to their impurities. They contain one or more phosphates of calcium inti- mately intermingled with other substances of both organic and inorganic origin. The organic substances are distinct fragments of skeletons of animals or diflfused pigments that impart a more or less definite color to the inorganic materials.

Some deposits contain a very small proportion of the phosphates, consisting in large part of other minerals, which are classed as impu- rities. Chemical analyses show that the most common impurities are the oxides of aluminum and iron, which occur in different fonns, the most prominent aluminum-bearing mineral being the hydrosili- cate kaolinite. The large proportion of phosphoric acid shown .by many of the analyses suggests that some of the alumina may be combined to f onn aluminum phosphates, either with or without iron.

Limonite is the most common iron-bearing mineral, though in the pebble-phosphate region glauconite is a constituent of the ''bedrock" (Alum Bluff formation). In many of the deposits the iron prob- ably occurs in the form of ferrous siUcate at depths where oxidation

' Eldridge, G. H., A preliminary sketch of the phosphates of Florida: Am. Inst. Min. Eng. Trans., voL 21, p. 231, 1893.

Mineralogy. S5

has not been very effective. The Umonite is usually disseminated through the other materials in such a way as to give them a sUght yellow or orange color, but in the overburden of some of the pebble- phosphate mines it is concentrated in the form of nodules that include more or less sand.

Vivianite (FesPzOg.SHjO) has been noted at some places, but it is probably rare, for its blue color would cause it to be recognized at once where it occurred in considerable quantity.

Silica is a very common constituent, occurring in coarse fragments that appear to have been more or less rounded by mechanical wear. In some parts of the phosphorites the sihca is evenly distributed; in others it is aggregated.

Magnesium oxide, which is given in a large number of analyses of phosphate, probably occurs most commonly as magnesite, but in a few phosphorites the large proportion of phosphoric acid and the small proportion of carbonic acid suggest that the magnesia is com- bined with the phosphoric acid to form magnesian phosphate.

The percentages of other substances determined in analyses of phosphate are so small that they are of Uttle consequence. In the most complete analyses small quantities of sodium and potassium are reported, and probably these elements occur either as carbonates or sulphates.

The minerals seen in thin sections of phosphorites are either isotropic or doubly refracting. The minerals that show double re- fraction occur as mammiUary incrustations on the surface of the isotropic material or as veins that more or less completely fill crevices. More rarely stalactites and stalagmites are found in cavities in the phosphorite. The incrustations are white, brown, yeUow, or greenish, have a resinous or vitreous luster, and appear either opaque or only slightly translucent when seen with the naked eye, but in thin sec- tions they appear transparent and colorless or white. Their hard- ness is somewhat variable, though the purest materials are about as hard as apatite, being approximately 5 by the Mohs scale. The crystalline fragments decrepitate when heated and form a white powder when pulverized. The index of refraction is about 1.6; the double refraction of some of the minerals is low and that of others is high. Many sections contain alternate bands that show different birefringence, one band being low and the next about twice as strong. The crystals are in the form of microscopic fibers arranged in radiating groups or with their longest dimensions at about right angles to the surface of the incrustations. The basal sections of some of the fibers show an interference figure that indicates a mineral which is uniaxial and negative. Other basal sections appear to contain another min- eral, which is optically positive.

86 Phosphate Deposits Of Florida.

In his discussion of the French phosphorites Lacroix describes two doubly refracting minerals having about the same optical char- acters as some of those found in the Florida phosphates. These are called dahUite and francolite, which may be distinguished by the presence of fluorine in francolite and it-s absence in dahlUte. Lacroix restricts the name staffelite to the fibrous variety of francolite. The presence of a third mineral, of unknown composition, was detected by the fact that it had a higher birefringence than dahllite and fran- coUte and was optically positive instead of negative.

Florida phosphate contains a uniaxial mineral of low double re- fraction corresponding in this and other optical properties to fran- coUte, and the presence of fluorine in the phosphate, as shown by the complete analyses, indicates that this mineral is francolite or its fibrous representative which Lacroix calls staffelite. The unknown mineral described by Lacroix may be represented by the crystals having a higher birefringence than francolite and a positive optical character.

The isotropic phosphorite of the French deposits has been called coUophanite and the variety containing fluorine has been called fluo- coUophanite. Mixtures of the isotropic collophanite with crystalline minerals Lacroix named quercyite, mixtures containing an opti- cally negative mineral he called o'-quercyite, and mixtures containing the unknown, optically positive mineral he called -quercyite.

The molecular ratios of the minerals in a few Florida phosphates have been calculated, CaO being taken as 100, as shown in the table on page 85. The numbers of the analyses are the same as those used in the tables on pages 71-81. In making the calculations the sihca (SiOj) has been omitted from analyses in which it was impossi- ble to determine whether the combined silica was included with the uncombined. The water (H2O) driven off below 105° C. was assumed to be hygroscopic, though in the absence of definite information con- cerning some of the analyses it is not certain that some of the com- bined water in the phosphate minerals may not have been driven off at a lower temperature. It should also be remembered that theo- retical combinations based on the analysis of impure material are more or less unreliable. For comparison there has been added to the table the average ratios obtained by calculating the analyses of the materials described by Lacroix.*

1 Lacroix, A., Sur la constitution min<raloglque des phosphorites franalses: Compt. Rand., voL 150, p. 1213, 1910; Minralogie de la France, vol. 4, pt. 2, p. 555, 1910.

Op. cit.

Schaller, W. T., MinenUogical notes, series 2: U. S. Qeol. Survey Bull. 500, pp. 08-100, 1012.

Minehaloqy.

Ratios computed from analyses of phosphates from Florida,

No.

Pa:eof this bul- letin.

CaO.

Co,.

F.

HfO.

AljO,.

FeiOa.

MgO.

Sio,.

K,0,

NSfO.

TiO,.

SOs.

lOO

(a\ (ai (a\ (a)

K

$"

1,527

(a)

1,555

/

fa) (a)

33A-. 79

33B . . 79

34 7fl

DLhllite&

Fronoolitefr

ColloplisnitA 6.

a Not computed.

b Ratios computed by Schaller from analyses of phosphate minwals.

The phosphates represented by the first seven analyses are more or less impure rock phosphates, and with one exception probably consist very largely of amorphous material. The description of No. 12 indi- cates that the sample was an incrustation on a mass of phosphorite, and though the original sample is not now available for examination, there is little doubt that the incrustation, like all the others that have been exainined, was largely crystalline.

The average ratios of analyses Nos. 1, 6, 7, 12, and 13 correspond to about 100CaO.29PA- 13F.7COa.l8HjO. For francoUte Schaller gives the ratios 100CaO.29P2O5.18F.7CO,.9H2O (mmus 90) and for the analysis of coUophanite containing fluorine lOOCaO.SOPjOg.SF.lOCOj. 44H3O. The analyses of the Florida rock phosphates agree in the ratios of the principal materials with the ratios of francoUte and coUophanite, the fluorine is more than that of the fluocoUophanite and less than that of the francoUte, and the proportion of H3O is higher than in francoUte and lower than in fluocoUophanite. Many thin sections of the rock phosphates contain both isotropic and doubly refracting minerals, and this fact, taken in connection with the analy- ses, suggests that the phosphorites are a mixture of francoUte and fluocoUophanite, with formulas which may be written 9CaO.3P2O5.CO3. HjO.CaFe and 9Ca0.3PA.CaO.COa.H30.nH;0.2HF. Analyses Nos. 8 and 9 show a higher ratio of P3O5 than is found in these minerals, and the presence of a large proportion of AI2O8 and FeOg suggests the occurrence of compounds of phosphate containing iron or aluminum, or both, together with the mixture of francoUte and fluocoUophanite.

i Schaller, W. T., op. cit., p. 99.

88 Phosphate Deposits Of Florida.

Analysis No. 25 represents a soft phosphate havmg the ratios 100CaO.3lP3O5.18F.7CO2.34H2O, or approximately the same as fluo- coUophanite with a somewhat smaller proportion of HjO because of the necessity of supplying some HgO to the compomids of iron and aluminum present. The natural presumption is that the nainerals francolite and fluocollophanite are present, and this presumption is strengthened by the intimate relation of the soft phosphate and the rock phosphate.

The ratios shown in analyses Nos. 31 and 32 do not admit of a close approximation to the formulas of any definite compounds, but the high proportions of PjOg, AlOg, and FcjOg suggest the presence of aluminum or iron phosphates, or both. The analysis of phospha- tized limestone (No. 35) gives ratios for CaO, P2O5, and COj in about the proportions of dahUite, francohte, or collophanitc, but in the absence of determinations of F and HjO it is not possible to determine which of these minerals is present. Analyses of pebble phosphate (samples Nos. 33, 34, and 36) are also incomplete and differ from the preceding only in the relatively small proportion of P3O5 and large proportion of CO,, which probably indicates the presence of calcium carbonate in addition to the phosphate minerals.

Analyses Nos. 38 and 39 represent pebble phosphates, the samples having been obtained by washing the matrix from the pebbles. The average values give 100CaO.28P2O5.14F.8CO2.24H2O. This formula is approximately the same as that deduced from the analjes of rock phosphates. The examination of thin sections shows a high per- centage of isotropic material, though a doubly refracting mineral is present in some sections. The natural inference is that the mineral composition is approximately the same as the rock phosphate and that the pebbles are probably a mixture of francolite and fluocol- lophanite. A slightly higher proportion of COj in analysis No. 40 is doubtless explained by the presence of a carbonate of calcium.

The matrix of a pebble phosphate is represented by analysb No. 46, which shows nearly the same ratios as the pebbles. A high proportion of HjO is explained by the fact that a portion of it was doubtless combined with the alumma and iron oxide.

The analyses of river-pebble phosphate Nos. 50, 51, and 52 give average values 100CaO.25PA-20F.llCO2.47H2O. This formula is slightly lower in PjOg and slightly higher in F and CO3 than that deduced for the other phosphates. The assumption that some of the CaO is combined with the excess of CO3 in analyses Nos. 50 and 51, and that some of the excess Ca is combined -with the F in analysis No. 52 would permit the combination of the remaining substances as fluocollophanite or as a mixture of fluocollophanite and francohte.

In the foregoing discussion of the analyses included in the table no attention has been given to the unknown mineral described by

Phosphate Mining. 89

Lacroix,* though some of the thin sections of rock phosphate show a mineral that, from its high birefringence and optically positive (?) character, has been tentatively identified as the unknown mineral. If this identification is correct the rock phosphates consist of both or-quercyite and /?-quercyite. The occurrence of francolite of the fibrous variety, staffeUte,* and the unknown mineral intimately intermingled and associated with the isotropic fiuocoUophanite show that the rock phosphates are a mixture of or-quercyite and Suercyite. A doubly refracting mineral occurs sparingly in the pebble phosphates, but it has a low birefringence and agrees in its other optical properties with dahllite and francohte. The presence of fluorine in the complete analyses indicates that this mineral is probably francolite. The pebble phosphates are therefore largely fluocollophanite or, where francolite is present, or-quercyite. Possi- bly further study will reveal the presence of the unknown mineral and thus the pebble phosphate may after further investigation be found to contain -quercyite.

The relations of the isotropic and crystalline minerals in the thin sections of Florida phosphates are suflBlciently clear to indicate the different stages of formation. As has already been stated, the crys- talline minerals occur as incrustations on exposed surfaces of the isotropic mineral or as veins in small openings. After the deposition of the isotropic portion of the phosphorite the cavities were wholly or partly filled with the crystaUine minerals. Reference to the analyses of the different phosphate samples wUl show that the pro- portion of impurities present is greater in the ordinary samples than in sample No. 12, which represents the comparatively pure incrus- tation found on the surface of the phosphorite. After the deposition of the isotropic portion of the phosphorite waters percolating through the deposit brought with them or dissolved a portion of the phosphate already formed and redeposited it in the form of crystalUne material that was much freer from impurities than the original phosphorite. This material was doubtless formed slowly and was arranged in crystalline form partly because of the rate of deposition and partly because the materials in solution were relatively free from foreign substances.

Phosphate Mining.

CLASaES OF PHOSPHATES MINED.

In Florida there are two classes of commercially important phos- phate — the rock phosphate and the land-pebble phosphate. Both types are mined by means of open pits, but the processes employed in the rock-phosphate region differ greatly from those employed in the land-pebble phosphate region. Moreover, there are minor differ-

1 lActoix, A., op. dt.

90 Phosphate Deposits Of Florida,

ences in the methods of mining in different parts of a single region. In discussing mining methods only the general processes involved will be considered. Local modifications of the general processes of exploiting the phosphate and preparing it for the market are desigixed to meet the requirements of the varying conditions of occmrence, axid the greater the degree of ingenuity and resourcefulness of the miner the more successful he will be in obtaining satisfactory results.

Bock Phosphate.

Stripping, — The first operation in mining rock phosphate is to remove the overburden of barren sand and clay — work that is usually done by horsepower scrapers, by picks and shovels, or, more rarely, by steam shovels. In some places hydraulic methods are employed, the overburden being first loosened by a hydraulic giant and washed into a pit, from which it is raised by a centrifugal pump and forced through pipes to the waste pile.

Excavating. — Rock phosphate was first mined by pick and shovel, and in some places nothing but the bowlders were saved. These, after being uncovered by the removal of soft phosphate, phosphatic pebbles, sand, and other debris, were broken up and the fragments were shipped to the market. Later some of the miners endeavored to recover a portion of the finer material. The phosphate was ex- cavated with pick and shovel and thrown upon a screen of mesh that permitted the clay and soft phosphate to pass through and to retain the coarser pebbles. By this method it was possible to save some of the pebbles as well as the bowlders.

With the introduction of log washers the cruder methods first used were abandoned. However, the pick and shovel are still used in most places where the mining is done above the level of groimd water, though in a few mines phosphate is excavated by steam shovels.

Soon after mining was begun it was discovered that much of the phosphate in the vicinity of Dunnellon and farther south was below the level of groimd water. At first attempts were made to lower the water level in the mines by pumping, but owing to the porous char- acter of the beds and the large volume of water they contained, the quantity of water entering the mines was large, so this method proved both difficult and expensive. Later steam dredges were mounted on wooden hulls and the phosphate was dredged from below water level. (See PI. XVII.) This method of mining proved satisfactory, and is in use now wherever phosphate is mined below the ground- water level. In some places the deposits lie partly above water and it is possible to remove a part of the phosphate with pick and shovel before dredging is begun. By dry mining it is easier to follow the trend of small pockets of phosphate, and a smaller amount of worth- less material is excavated than with a dredge.

§1 it

Phosphate Mining. 91

Raising and vxisMng, — After it has been excavated the phosphate

and its matrix, consisting of a number of substances, is conveyed to

the "waslier. Some phosphate was formerly raised from the pits

by means of buckets attached to cables, but it is all now loaded on

small cars and drawn up inclined railways by means of cables. The

phosphate is dumped from these cars on a screen composed of parallel

iron bars C grizzly'' bars), 2 to 2 J inches apart. The finer material,

consisting of sand, clay, soft phosphate, and pebbles, is washed

through, the openings between the bars by a jet of water. Bowlders

too large to pass between the ''grizzly'' bars are broken with a

sledge hammer or with dynamite. Occasionally the steam shovel

or dredge raises a bowlder too large to be dumped into the hoisting

cars, and so it is broken by blasting with dynamite, a stick of which

is placed on the bowlder, covered with mud or wet sand, and then

exploded.

After passing through the grizzly bars the phosphate is broken in a crusher and then washed in a trough containing two or four revolving logs, each about 30 feet long and 18 inches in diameter arranged in pairs, and each log fitted with blades that pass between the blades on the opposite log. The logs rotate in opposite direc- tions, and the blades are so adjusted as to give the pebbles and broken fragments of bowlders a movement in one direction, the logs being so inclined that a stream of water flowing in the opposite direction removes the fine material and conveys it through troughs to the waste heap.

From the logs the phosphate passes through two cylindrical screens, 12 to 14 feet long, placed one inside the other and con- taining openings large enough to permit day and fine sand to escape. The inner screen is perforated by openings measuring IJ inches by three-eighths of an inch; the outer by openings measuring one-eighth by one-sixteenth of an inch.

In its passage through the screens the phosphate is washed by jets of water ejected from a perforated pipe situated inside of the screen and by water from similar pipes on the outside of the outer screens. This removes the sand and clay that still adheres to the phosphate.

Sorting, — The coarser phosphate, held on the inner screen, falls upon a circular wooden table, while the finer material from the outer screen passes directly to the ''wet" bin below this table. The table carrying the coarse material revolves slowly and a number of men and boys who stand about it remove the fragments of lime- stone, clay, and flint that are mixed with the phosphate. At the end of a complete revolution the phosphate is automatically scraped from the table C picking belt") and falls into the ''wet" bhi with the finer material.

PHOSPHAl'E DEPOSITS OP FL6Blt>A.

Drying, — From the "wet' bin the phosphate is conveyed in a small car running on a narrow track to the upper part of the dry- shed. This shed consists of a floor, upright wooden posts, and a roof that usually projects several feet beyond the edge of the slied. Boards are nailed about the lower part of the bin to prevent the phosphate from being lost, and in bad weather some of the sheds are boarded up several feet from the bottom to exclude rain.

In these sheds the rock is thoroughly dried by placing a layer of phosphate about 2 feet thick on the floor and stacking wood upon it to a depth of about 2 feet. This wood is so arranged that one layer lies across the other and considerable space is left between the sticks. Phosphate rock is dumped upon the wood to a depth of 10 to 15 feet and the wood is then fired and allowed to bum until it is con- sumed. The rock is ready for shipment as soon as it is cool enough to be loaded on cars. At some mines the rock is dried in rotary metal cyhnders similar to those used at the pebble-phosphate mines, but this method is seldom used in the rock-phosphate region.

VaMe products, — In the process of mining and washing rock phosphate a great deal of material not suited to the requirements of the market is rejected. Possibly much of this will be utiUzed at some future time, though the present demand is too small to make market- ing profitable. Phosphate of lower grade than the market specifica- tions is, as far as possible, left in the pit. In dredging it is necessary to excavate both low and high grade material, because it is impossible to tell in advance what sort of material wiU be obtained. After being washed much of the low-grade rock is rejected unless it is rich enough to be brought to market requirements by admixture with higher- grade rock.

In addition to the loss of low-grade rock, a large amoxmt of soft phosphate is washed into the waste heap and some phosphate is re- moved from the picking table through mistake or because it is intimately associated with such substances as limestone or flint. It is impossible to determine exactly how much phosphate goes to the waste heap, but it has been estimated at two or three times the amount saved.

Pebble Phosphate.

Stripping. — Before land-pebble phosphate can be mined it is necessary to remove the overburden, consisting of a varying thick- ness of sand or of friable sand rock. This overlying material is re- moved by hydrauUc giants or by steam shovels. In hydraulicking, the sand is loosened by a jet of water and washed into a hole, from which it is removed by centrifugal pumps and conveyed through pipes to the waste heap.

The steam shovel is used in removing the overburden at a number of mines and is especially appUcable to deposits in which the sand is

Phosphate Mining. 93

partly indurated or contains hard lumps, such as concretions of iron oxide that are too large to be handled by centrifugal pumps. The overburden is Ufted by the steam shovels and dumped into small cars run on a temporary track. These cars are hauled to the waste heap, unloaded, and returned to the excavation to be refilled.

Excavating. — Nearly all the land-pebble phosphate is excavated by hydraulic methods, the rock being loosened and washed into a depres- sion (sump hole) by a hydrauhc giant. From the sump hole the phosphate and matrix are removed by one or more centrifugal pumps and conveyed through pipes to the washer. At some plants it is necessary to use a second pump to raise the phosphate to the top of the washer. At one mine the phosphate is excavated by a steam shovel, which is placed on a temporary track and operated by lower- ing a scoop attached to cables, by which the phosphate is hoisted from the pit and dumped on small cars to be hauled by cable to the sheds.

Washing. — The washers in the land-pebble phosphate region are of the same general type as those used in the rock-phosphate region, though they vary considerably in details of construction. From the hoisting pumps the phosphate is forced through the pipes to the washer and dumped on a cylindrical screen containing openings an inch in diam- eter. The screen is about 12 feet long and 4 feet in diameter, and is inclined, the upper end being about 2 feet higher than the lower. The phosphate passes through the openings and the lumps of clay and other debris retained on the screen are discharged into a trough that conveys them to the waste heap.

After passing through the openings in the separating screen the phosphate pebbles fall upon a second screen, about 18 feet long and 6 feet wide. This screen is inclined, one end being about 18 inches higher than the other, and the phosphate is washed across it by a stream of water. About half the area of the screen is occupied by perforations half an inch long by one-sixteenth of an inch wide. In passing over this screen the material is freed from much of its fine sand and clay, which pass through the perforations in the screen and enter the waste trough along with the day balls and other debris.

The rock next passes through logs similar in arrangement and adjustment to those used in washing rock phosphate. The logs of the pebble-phosphate washers are, however, shorter, generally only about 18 feet long. There are four of them, arranged in pairs. The logs are inclined in the direction opposite to the way the phosphate is moving, at a slope, according to MendenhaU,* of about 1 to 24; in other words, one end of the pair of logs is about 9 inches higher than the other. A stream of water flowing through the trough containing

1 Mendenhall, H. I)., Modem land-pebble phosphate mining plants In Florida: Eng. News, vol. 60, No. 16, p. 413, Oct. 15, 1908.

94 Phosphate Deposits Op Florida.

the logs carries the fine sand and day out of the trough in one direc- tion as the phosphate is carried in the other direction by the flanges or blades on the logs.

From the first pair of logs the phosphate passes into a 12-foot screen composed of two revolving cylinders, one inside the other, the outer one having a diameter of about 4 feet and the inner one of about 3 feet. The rock in the screen is washed by jets of water thrown from perforated pipes inside and outside the screen. The cylinders contam perforations measuring one-half by one-sixteenth inch, and are inclined in the direction in which the rock is moving, the differ- ence in the height of the two efids being about a foot. On the inside of the screen there are ridges which, as the screen rotates, agitate the rock and cause it to be more thoroughly washed.

From this screen the rock passes through another pair of logs, which are duplicates of the first pair, and from these it goes to a screen like the one just described. From the last screen the rock falls into a hopper and is conveyed by cars to the dry shed, where it is dumped into a 'wef bin.

Sorting. — The picking table is not so important a part of the equip- ment of the washer in the pebble-phosphate region as in the rock- phosphate region, for the pebble phosphate is nearly all fine, and sorting by hand would be a very slow process. However, hand sorting is done at some mines, chiefly to remove clay balls and like debris.

Drying, — From the wet bin the rock is carried in buckets, attached to a belt, to the driers. These driers are revolving cylinders, resem- bling those used in the manufacture of Portland cement, though somewhat smaller. They are so inclhied that the material passes slowly through them by gravity. Longitudinal ridges on the inside of the cylinder cause the rock to fall through the heated air as the cylinder is rotated. The heat is applied at the upper end, and in passiug the length of the cylinder (about 30 feet) the rock is thor- oughly dried. Mines that handle 3,000 tons of rock in 24 hours operate about 10 cylindrical driere.

From the driers the rock is conveyed to a car placed on scales, and after being weighed is dumped in the dry bins. From the dry bins it is carried by gravity to cars to be shipped to market.

Waste 'products. — The amount of phosphate lost in mining the pebble phosphate is probably less than in mining the rock phosphate, be- cause the matrix of the pebble phosphate is predominantly sandy, whereas that of the rock phosphate is usually clayey and contains much soft phosphate. However, there is considerable clay and solt phosphate in the finer-grained portions of the pebble phosphate, and practically all this material goes to the waste heap either as finely comminuted sediment or as clay balls.

Phosphate Deposits Of Florida. 95

Bibliography Of Florida Phosphates.

This bibliography has been compiled from existing bibliographies and an examination of the literature. Many of the publications listed give only incidental reference to the phosphate deposits of Florida, but some such papers contain important facts.

Anonymous: Florida phosphates in 1910: Eng. and Min. Jour., vol. 91, p. 796, 1911.

L'exploitation des phosphates en Floride; La Soci6t "La Floridienne":

L'Engrais, vol. 18, p. 327, 1903.

Di3 Bestimmung der Sesquioxide [iron and aluminum] in Phosphaten: Chem.

Zeitung, vol. 23, p. 647, 1899. BLA.IR, A. W., Ground phosphate rock as a source of phosphoric acid: Florida Agr.

Exper. Sta. Press Bull. 77, 1908. Brown, L. P., The phosphate deposits of the Southern States: Eng. Assoc. South

Proc, vol. 15, No. 2, p. 53, 1904. The phosphate deposits of continental North America: Eighth Internat.

Cong. Applied Chemistry, vol. 26, p. 87, 1912. BrnsMAN, H. J., Contributions siu* lee phosphates de la Floride: Recueil des Trav.

chim., vol. 11, p. 286, 1893. BuTOENBACH, Les phosphatos de la Floride: L'Engrais, vol. 18, p. 1047, 1903. Carnot, Adolphe, Sur les variations observe dans la composition des apatites, des

phosphorites et des phosphates simentaires: Annalee des mines, vol. 10, p. 137,

Codington, E. W., The Florida phosphates: Am. Inst. Min. Eng. Trans., vol. 25,

p. 423, 1896. CoLLisoN, S. E., The phosphate deposits of the United States: The Florida Pennant,

Agr. Number, p. 37, 1911. Cox, E. T., An extensive deposit of phosphate rock in Florida: Am. Naturalist, vol.

24, p. 1185, 1890. Floridite, a new variety of phosphate of lime: Am. Assoc. Adv. Sci. Proc.,

vol. 39, p. 260, 1891.

The land and river pebble phosphate deposits of Florida (title only): Am.

Assoc. Adv.- Sci. Proc, vol. 40, p. 190, 1891.

The Albion phosphate district: Am. Inst. Min. Eng. Trans., vol. 25, p. 36,

Geological sketch of Florida: Am. Inst. Min. Eng. Trans., vol. 25, p. 28,

Dall, W. n.. On the age of the Peace Creek beds, Florida: Philadelphia Acad. Nat.

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Bull. 84. 1892. Barton, N. H., Notes on the geology of the Florida phosphates: Am. Jour. Sci., 3d

ser., vol. 41, p. 102, 1891; abstract in Eng. and Min. Jour., vol. 51, p. 210, 1891. Davidson, W. B. M., Suggestions as to the origin and deposition of the Florida phos- phates: Eng. and Min. Jour., vol. 51, p. 628, 1891. Florida phosphates — origin of the bowlder phosphate of the Withlacoochee

River district: Eng. and Min. Joiur., vol. 53, p. 42, 1892.

Notes on the geological origin of phosphate of lime in the United States and

Canada: Am. Inst. Min. Eng, Trons., vol. 21, p. 139, 1893.

96 Phosphate Deposits Op Flobida,

De Launat, L., New depodts of phoephates in the peninmila of Florida and their

exploitation: Ruaedan Jour. Mines, vol. 12, p. 536, 1892. Eldridge, G. n., Preliminaiy sketch of the phosphates of Florida: Am. Inst. Min.

Eng. Trans., vol. 21, p. 196, 1893. FxjLLBK, M. S., Phosphate rock: U. S. Geol. Snrvey Mineral Keeouices, 1906, pp.

1079-1090, 1907. Goldsmith, Edw., Pealike phosphorite from Polk County, Fla.: Philadelfdiia Acad.

Nat. Sci. Proc., 1890, p. 10, 1891. Gbothe, O., Mining of phosphates, with special reference to Florida phosphate:

Deutsch. Am. Tech. Verbandes Techn. Mitt., vol. 15, p. 1, 1910. Ha WES, G. W., On a phosphatic sandstone from Hawthorn, in Florida: U. S. Nat.

MuB. Proc. 1882, p. 46, 1883. HovEY, E. 0., Phosphate rock: U. S. Geol. Survey Mineral Resources, 1903, pp.

1047-1058, 1904; idem, 1904, pp. 1053-1064, 1905; idem, 1905, pp. 1117-1126, 1006. Jackson, Granberrt, Mechanical drying of phosphate rock: Eng. Assoc. South

Trans., vol. 18, pp. 95-120, 1907. Johnson, L. C, Phosphatic rocks of Florida: Science, vol. 5, p. 396, 1885. Notes on the geology of Florida — two of the lesser but typical phosphate

fields: Am. Jour. Sci., 3d ser., vol. 45, p. 497, 1893. Jumeau, L. p., Composition des gbements de phosphate de chaux des tats-Unis:

Annales de chimie anal., p. 412, 1906. Le phosphate de chaux (gisements connus) et les exploitations aux ltats-ITnis

en 1905, Veuve Ch. Dunod, Paris, 1905. KosT, J., Florida State Geological Survey, Tallahassee, 1887. Abstract in Science,

vol. 9, pp. 44-447, 1887. Lb Baron, J. F., Discussion of paper by W. B. M. Davidson on the geological origin

of phosphate of lime in the United States and Canada: Am. Inst. Mm. Eng., Balti- more meeting, Feb., 1892; published 1893. Ledoux, A. R., The phosphate beds of Florida: New York Acad. Sci. Trans., vol. 9,

p. 84, 1890; Eng. and Min. Jour., vol. 49, p. 173, 1890; Sci. Am. Suppl., vol. 30,

p. 12104, 1890. Levat, E. D., !tude sur Tindustrie des phosphates et superphosphates (Tunisie;

Floride; scories basiques): Annales des mines, vol. 7, p. 1, 1895; abstract in Soc.

chimique Bull., 3d ser., vol. 13, p. 602, 1895. McCallie, S. W., a preliminary report on the phosphates and marls of Geoigia:

Georgia Geol. Survey Bull. 5-A, 1896. MAizii:REs, Les expeditions des phosphates de la Floride aux tats-Unis et traDgers

depuis 1890-1896: L'Engrais, vol. 12, p. 108, 1897. Matson, G. C, and Clapp, F. G., A preliminary report on the geology of Florida,

with special reference to the stratigraphy: Florida Geol. Survey Second Ann.

Rept., p. 21, 1909. Memminger, C. G., Progress in the phosphate mining of the United States, 1900:

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method of prospecting, mining, and preparing for market: Am. Fertilizer, vol. 23,

pt. 1, p. 5, 1905. Pebble phosphate — review of the existing conditions and future outlook of the

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Eng. News, vol. 60, No. 16, pp. 410-414, 1908.

Bibliography. 97

MiLXJWR, C. C. H., The phosphate fields of Florida, 48 pp., London, Eden. Fisher & Co,, 1891.

Florida, South Carolina, and Canadian phosphates. London, Eden, Fisher &

Co., 1892. MxTRitAY, Sir John, Report on the specimens of bottom deposits; Report on results of dredging under the supervision of Alexander Agassiz in the Gulf of Mexico, in the Caribbean, and along the Atlantic coast of the United States by the U. S. S. Blake: Harvard Coll. Mus. Comp. Zool., vol. 12, No. 2, p. 37, 1885; abstract in Am. Jour. Sci., 3d ser., vol. 31, p. 221, 1886. Parker, E. W., Phosphate rock: U. S. Geol. Survey Twenty-first Ann. Rept., pt. 6, pp. 481-502, 1901; U. S. Geol. Survey Mineral Resources, 1900, pp. 803-814, 1901. Patterson, H. J., Phosphates, phosphatic or phosphoric acid fertilizers: Pennsyl- vania Dept. Agr. Bull. 94, 1902. Pkmrose, R. a. F., Jr., Nature and origin of deposits of phosphate of lime, with an

introduction by N. S. Shaler: U. S. Geol. Survey Bull. 46, 1888. Persons, A. A., Soils and fertilizers: Florida Agr. Exper. Sta. Bull. 20, p. 16, 1893. Phillips, W. B., Florida land-pebble phosphates: Eng. and Min. Joiu*., vol. 69,

p. 201, 1900. PiCKEL, J. M., Florida phosphate: Florida Agr. Exper. Sta. Bull. 10, p. 6, 1890. Comparative value of raw, finely powdered phosphate and of acidulated phos- phate as a fertilizer: Florida Agr. Exper. Sta. Bull. 13, p. 12, 1891. Pratt, N. A., Florida phosphates — the origin of the bowlder phosphates of the With-

lacoochee River district: Eng. and Min. Jour., vol. 53, p. 380, 1892. ScHRADER, Jay, The underground wealth and prehistoric wonders of Polk and De Soto>

counties, Bartow, 1890. Hidden treasures, Bartow, 1891. (Extract included in "The phosphate in- dustry of Florida,'* by C. D. Wright, Commissioner of Labor, Sixth Special Rept. p. 39, 1893.) Sellards, E. H., Production of phosphate rock in Flonda: Florida State Hort. Soc.

Trans., p. 138, 1909. A preliminary paper on the Florida phosphate deposits: Florida Geol. Survey- Third Ann. Rept., p. 17, 1910.

American phosphate deposits in their relation to national agricultimd develop-

ment: Twelfth Ann. Convention Southern States Assoc. Commissioners of Agr. Proc., p. 60, 1911.

Mineral resources of Florida: Florida Geol. Survey, 1908 to 1913, inclusive.

Shaler, N. S., Residual ablation deposits (contained in a paper entitled "A pre- liminary sketch of the phosphates of Florida," by G. H. Eldridge): Am. Inst. Min. Eng. Trans., vol. 21, 1893.

Shepard, C. U., The development and extent of the fertilizer industry: Am. Chem. Soc. Jour., vol. 15, No. 6, 1893.

SMirH, E. A., Report on the cotton production of the State of Florida, with an account of the general agricultural features of the State: U. S. Tenth Census, vol. 6, pt. 2, p. 175, 1884.

Phosphatic rocks of Florida: Science, vol. 5, p. 395, 1885.

Stone, C. A., Mining and milling Florida phosphates: Eng. and Min. Jour., vol. 88, p. 2, 1909.

Struthers, Joseph, Phosphate rock: U. S. Geol. Survey Mineral Resources, 1901, pp. 811-822, 1902; idem, 1902, pp. 915-920, 1904.

Tucker, J. F., The phosphate industry of the United States, prepared by C. D Wright, Commissioner of Labor, 1893.

85816<— Bull. 604—15 7

98 Phosphate Deposits Of Florida.

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Index,

A.

Page.

A|se of tlie pbosphftte depoBiti 45-

Agrioolay section in phoB|bateinin at 43

Alachua clay, age of 20

distributioa and chaiacter oL 20-31

Alum formatkny oontact of, with over- lylng Bone Valley giavel, plate

showing 06

distribution and character of. 13-15

phosphate of. 58-64

analyses of. 76-79

character of. 33-35

Animals, Jawbone and teeth of, plate showing 37

Apalachicola group, phosphates of, age of 68 60

rock phosphate of, must be discriminated

from that of the Vicksburg group . 40

subdivisions of 113

Apalachicolan time, depth of water in 61

B.

Bartow, section 1 mile north of 81

Bedrock of the phosphate miners, character of 33-35 See also Alum BhiH formation.

Bibliography of Florida phosphates 05-08

Bone Valley gravel, age of 21,80

contact of, with underlying Alum Bluff

formation, plate showing 66

distribution and character of. 21-22

phosphate of, character of. 35-44

origin of 65-66

size and shape of deposits of 37-38

Bowlders, formation of 50-51

phosphate, embedded in a matrix, plate

showing 24

structure of. 24

Bowling Oreen, section in mine at 44

Caloosahatcbee marl, distribution and char- acter of 10-20

Charleston Mining Co. 's mine No. 1 , section in 43 Chatard, T. M., analyses by. .72,73,74,75,80-81,82,84 Chattahoochee formation, distribution and

character of. 13

Chazal, Dr., acknowledgment to 81

Chert, occurrence of, in the Bone Valley gravel 37 Choctawhatchee marl, distribution and char- acter of 15-16

CoUophanite, occurrence of 86

Commercial requb-ements in phosphates 60-70

Crystalline phosphate minerals in cavities,

plates showing 24,25,52

Cummer Lumber Co.'s mine, nature of de- posit at 40-50

plate showing 50

relations of rock phosphate to underlying

limestone in, plate showing 50

D.

Page.

Dahllite, occurrence of. 86

Pall, W.H., cited 47

fosails determined by 14-15

Barton, N. H., cited 46-47

Deformation of phosphate deposits, processes

of. 27-38

Dominion, sections in mines at 42,43

Domini(m Phosphate Co.'s mine, section at. . 43 Dunnellon district, phosphate mines In, de- scription of 0, 31-32

E.

Eldrldge, G . II., cited 48, 81

Ellis, R. N., acknowledgment to. 16

F.

Fslrohild, J. G., analyses by 71,78,83

Flint, bowlders of, hi a phosphate deposit,

plate showing 27

nodules and bowlders of, how formed. ... 51

oocurrMiee of 36

Florida, peninsula of, submergence and emer- gence of C3

phosphate deposits of> map showing 10

Fluocollophanite , occurrence of 86

Formation of rock phosphate in place 40-

Fort Meade , phosphate deposits near 42-44

section in mine at 43

Fossils from hard-rock phosphate, determina- tions of 67-68

from the Alachua clay, report on 20

from the Alum Bluff formation, report on. 14-15 from the Bone Valley gravel, character of. 36-37 from the Bone Valley gravel, report on. . 21

from the Pliocene deposits lS-19

Francolite , occurrence of 88

Geolcy of th peninsular portion of Florida,

map showing In pocket.

Gidley, J. W., cited 68

fossils determined by 19,20,21

Guano as a source of phosphoric acid 55-56

Hawthorn formation, abandonment of name. 1 1 Hernando, phosphate mines near, description

of 32-33

Herzog, H., jr., analyses by 71,79

Hippturlon, fossil remains of 67-68

Howe,A. B., analyses by 77

International Phosphate Co.'s mine, section

in 44

Index.

J.

Page.

Jacksoavllle , log of well at 16-17

Jacksonville formation, distribution and

character of. 16-18

Jumaau, P., analysis by 76

K. KaoUnite, occurrence of. 84

Land-pebble phosphate, age of. 69

analyses of. 79,80,81

deposits of 10

character of. 35-44

general features of 7

matrix of, analyses of 82

origin of 6IW6

production of 8

waste ftom 82-83

Limestone as a source of phosphoric acid 5.V55

oocurrenceof 26

phosphatlxed, of the Alum Dlufl forma- tion, plate showing 34

of Vicksburg group, plate showing. . . 51 pillars of, in a phosphate deposit, plate

showing 27

Limonite, occurrence of 84-85

M.

Ifagstflte , occurrence of 85

Malta, phosphatic nodules of 63-64

UnrtfctiTiA limestone, distribution and charar-

terof 12

Marine phosphatic nodules, distribution and

character of. 58-61

origin of 61-64

Marl, phosphatic, analysis of 83

phosphatic, character and uses of 44-45

development of: 45

Mastodon, fossil remains of 67-68

part of the Jawbone of, plates showing. . . 36

part of the tusk of, plate showing 36

tooth of, plateshowing 36

Matrix of land-pebble phosphate, analysis of. 82

of the phosphate rock, character of 25-26

Medulla, section of well near 34

Mlnefidogy of the phosphate deposits 84-80

Mining by dredging, plate showing 90

Miocene series, representatives of 15

Movement in phosphate deposits, causes of. . 51 Mulberry, pebble phosphates from, analyses

of 80-81

phosphate deposits near 40-42

Murray, Sir John, cited 59-61,63,64

N.

Nashua marl, distribution and character of. . 19-20 Newberry district, phosphate mines in, de- scription of 29-31

Nodules, formation of 50

Northern part of the region, phosphate de- posits in .3H-39

O.

Ocala limestone, distribution and Hmracter of 12 Oligooene formations, upper, as a source of

phosphoric acid 57-

Oose of the Gulf Stream, anal-sis of 60

Overburden, character of. 26-27.37

P.

Page.

Palmetto Phoq>hate Co. 'a mine No. 1, aeo-

Uonin. 42

No. 2, section in 42

Peace Creek bone bed, possible age and char- acter of 19-20, 43

Peace River, jection on west bank of 45

Pebble phosphate, coarse semiinduiated,

plateshowing 34

general features of. 7

method of mining 91-94

undulating layers of, plate showing 66

Sft al30 Land-pebble phosphate and River-pebble phosphate. Peninsular limestone, distribution and char- acter of 12

Phosphate Mining Corpocation, mine of, sec- tion in 43

pit No. 3 of, section in 43

Phosphatization, proceasof 50

Phosphork! acid, source of 53-,63-64

Pierce Phosphate Co. 's mine, sections in 41-42

Plate-rock phosphate, broken, cemented by

phosphate, plate showing 26

deposits of. 9-10

descripttonof 34-25

platesshowing 26,51

Pleistocene deposits, distribution and charac- ter of 22-23

Pleistocene sands resting unconfonnably on phosphate and semiindurated

sands, plate showing 27

Pliocene series, representatives of. 18

Prairie Pebble Phosphate Co.'s mine, section

in 40

Production, record of 7-8

Q. Quartz, occurrence of, in the Bone Valley

gravel 37

Quaternary series, representatives of 22-23

R.

Recent deposits, distribution and character

of. Zi

Redeposlted phosphate, arrangement of 52-

position of. 66

production of. 8

source of. 66-67

River-pebble phosphate, age of. 69

analyses of 84

character of. 45

deposits of 10

general features of. 7

Rock phosphate, analyses of. 70-7.5

deposits of 9-10

size and shape of 28

description of. 24-25

formation of, in place 49-52

general feature? of 7

method of mining 90-92

of the Vicksburg group, must be discrim- inated from that of the Apalach-

icola group 49

origin of 46-49

Rock-phosphate mine, plate showing. 8

Royster, section in mineat 43

Index.

8. Page.

s,E.H.,cited

SilJoa,oooaiTenoeo( 85

Soft phosphate, analyses of 75,76

deposits of. 10-11

Svnentl features of. 7

in matrix of rock phosphate 25-26

wlginof 61-62

StelactlteB, phosphatic, plates showing 24, 52

Standard of parity for rock phosptiate 70

Stalger, George, analyses by 72

T.

Tampa teoHldoQ, distribution and chaiao-

lerof 13

Page.

Tiger Bay, section fn mine at 42

Tilghman Phosphate Co.'s mine, section in. . 44

Vaaghan, T. W., cited 61

Vicksburg group, distribution and character

oL 11-12

rock phosphate of, origin oL 460

Vivianite, occurrenoeof 85

W.

Waggaman,W.H., analyses by 74,75,76,83

cited 74,76,82-83

Waste material, composition of. 75-76

disposal of. 92,94

O

k

lb

t