A Preliminary Sketch of the Phosphates of Florida

George Homans Eldridge · 1892 · Historical

A Preliminary Sketch of the Phosphates of Florida by George Homans Eldridge (1892). 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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Preliminary Sketch

Of The

DHOppATEp OF FLORIDA.

By

Geo. H. Eldridge,

U. 8. OEOLOOICAI. 8UBVET, WASHIMOTONj S. C.

A Paper read before the American Institute of Mining Enoinesrs.

Author'S Edition. ' '1892.

r

A Preliminary Sketch Of The Phosphates Of

Florida,

By Oeorge H. Eldridqe,* U. S. Geological Survey, Washington, D. 0.

Development of the Industry.

The existence of phosphate of lime within the State of Florida has been known for over a decade; but until the spring of 1887, the extent and value of its deposits, possibly with one exception, were unsuspected. In that year Col. T. S. Moorehead, induced by a statement made by Mr. J. F. Le Baron, examined the gravels of the Peace river, recognized the importance of the deposits-, acquired such tracts as were regarded as desirable, and established the pebble-phos- phate industry, making his first shipment in May, 1888, to the Scott Manufacturing Company, of Atlanta, Ga.

The establishment of the pebble-phosphate industry upon Peace river was followed, a year later, by the discovery in Marion county of an entirely different class of phosphate, now commonly known as hard-rock phosphate. This discovery was made early in June, 1889, by Mr. Albertus Voght, in a well which he was sinking upon his place near the site of the present town of Dunnellon, about 20 miles southwest of Ocala. To it, more than to any other cause, is due the rapid and remarkable development of the present great in- dustry of the State. It was, however, Mr. John F. Dunn, of Ocala, who turned to advantage the accidental discovery of Mr. Voght. Afler acquiring a knowledge as to the chemical composition and value of the material, Mr. Dunn and his associates purchased several thousand acres of land and organized the Jt)annellon Phosphate Company for active operations. From Dunnellon as a center, pros- pecting rapidly extended in all directions, until at the present day important mines have been opened over a well-defined tract more than 200 miles long and about 6 miles wide. This tract lies par- allel to the Gulf coast, at an average distance from it of about 20 miles, and extends from the vicinity of Richland, in Pasco county, northward and westward nearly to the Apalachicola river.

Presented with the permission of the Director of the U. S. Geological Survey.

Preliminary Sketch Of The Phosphates Op Florida.

Preliminary Sketch Op The Phosphates Of Florida. 3

s

The region next attracting attention lay to the south of the hard- rock area, in the vicinity of Bartow, in Polk county. This is the now important field of land-pebble phosphate, the prospecting of which began in the latter part of 1890.

At the present day, phosphates of one description or another, of varying value, have been recognized from considerably west of the Apalachicola river, eastward and southward to nearly 60 miles south of the Caloosahatchee river. In all the districts mentioned, mining is conducted on a large scale, the shipments constituting a heavy item in the freights of the several railroads of the State. Not only is the raw material consumed in large quantities in the United States, but heavy shipments are also made to various ports in Europe.

Topography.

The topography of Florida is the result pf dynamic agencies com- bined with processes of sedimentation, erosion, and chemical solu- tion. While the western portion of the State is the direct southern extension of the coastal plain of the Atlantic and Gulf States, and is, therefore, a region in the evolution of which sedimentation has formed a prominent feature, the peninsular portion, on the contrary, had an independent origin, and is probably a modification of the emerged crest of an anticlinal fold that extends for many miles beneath the sea on either side.

The high upland region of northern Florida with its undulating surface, red soil and cultivated fields, presents the characteristic to- pography of the Lafayette formation, by which it is underlain. The southern limit of this elevated area, 20 to 40 miles south of the State line, mad west of the Suwanee river is marked by a somewhat abrupt and serrated slope, separating the uplands from the low, level, " flat-woods " country and swamp-lands which are underlain by horizontal Miocene strata and occupy the State thence to the coast ; east of the Suwanee river the topography of the coastal plain merges into that of the peninsula proper.

The topography of peninsular Florida exhibits two phases : the one, that of a comparatively high, undulating country; the other, that of flat lowlands. The former is limited to a broad median belt in the northern half of the peninsula ; the latter, with slight modi- fication, constitutes the entire southern half of the peninsula, and in the northern half forms along the coast a border to the more ele- vated central region. The drainage of the peninsula is essentially north and south, although all the streams have, along some portion

4 Prelimikaby Sketch Of The Phosphates Op Florida.

of their length, ao east and west course, which carries them from the interior towards the periphery of the State. The chief rivers of the peninsula are: on the east side, the St. Johns and the Kissimmee systems, now connected by canals, the latter draining into the Gulf through the Caloosahatchee river; in the central, more elevated re- gion, the Ocklawaha; on the west side, the Santa F6, Suwanee, Withlacoochee, and Peace rivers. The water-sheds of these streams are nowhere more than 250 or 300 feet above sea-level. Over much of the central area there is a vast detail of topography within slight vertical range which modifies the surface into a confused mass of hills, a feature largely due to the superficial deposits of sands, laid down just before the last emergence of the peninsula from the sea. In the lowland region, the elevations between the rivers are hardly percep- tible, except, again, for local modifications by sand-deposits ; the streams are sunk with sharp banks to varying 'depths beneath the general surface; the topography is, in fact, that of an extended, monotonous, though often timbered prairie.

The western side of the peninsula is that with which this paper is especially concerned. With the exception of the river-pebble de- posits of Black creek, about 25 miles south-southwest of Jackson- ville, the entire phosphate-belt, as at present developed, is confined to this region. The formations involved are of several ages, and the topography varies accordingly. From the vicinity of Dade City, in Pasco county, northward nearly to the State line, the country is under- lain by a broad belt of Eocene limestones, of considerable thickness and without stratification-planes. Their soft materials have been subjected to erosion and solvent processes both at and beneath the surface. The rock is channeled by underground streams, the presence of which is determined by their effects, seen in numerous sink-holes throughout the area of the formation. Depressions occupied by large bodies of water are at times emptied of their contents through these openings and channels, and it is further probable that extended tracts of land have been converted into lakes by the general lower- ing of the surface through the removal of masses of the underlying limestone. The Eocene area of the rock-phosphates of Florida is, therefore, undulating and irregular, an effect further heightened by the deposits of sands from the last submergence. Beneath the region of hard-rock phosphates in western Florida, however, the formation is of Miocene age, and consists of thin-bedded, horizontal limestones. The topography is, therefore, that of the "flat-woods" and swampy lowlands, with natural bridges but with few sinks. The general ele-

Preijminaby Sketch Op The Phosphates Of Florida. 5

vatioD of the rock-phosphate regions is less than 75 feet above sea- level.

In the angle of the South Florida and Florida Southern railroads, in the vicinity of Lakeland and Bartow, lies the water-shed of the region to the south and west. It reaches an altitude of 208 feet at Lakeland, but rapidly falls with the drainage to 117 feet at Bartow, 131 at Plant City, and elevations still lower as the coast is ap- proached. The underlying beds are marls, clays, and pebble-phos- phate, which give it a topographical aspect differing considerably from that of the regions just described. With some exceptions, its general appearance is that of the "flat- woods" lowland country, modified into a gently undulating surfade by the superficial deposits of sands. As the coast is approached, it graduates into the vast reaches of flat lowlands so characteristic of south Florida and the general coastal border of the State. The region of the Peace, Alafia, Mana- tee, and Caloosahatchee rivers, and of the great lakes which the last drains, is of the true lowland type, but is locally modified to an irregular surface by the superficial sands.

There are evidences throughout the phosphate-region, and also in many other portions of Florida, of the great predominance of chemi- cal solution over mechanical abrasion in the cutting of stream- courses and the moulding of general topographical features. No- where in the United States are these forces to be observed in such prevalence at the present day, and nowhere are the evidences of their past action and their agency in the development of both topography and geology so abundant.

The phosphate-rions of Florida are covered either with a heavy growth of pines, as in the sandy areas, or with deciduous growths, as in the region of sinks and in the peculiar areas known as hum- mock-lands. In the swamp-lands, cypress, oak, gum, ash, magnolia, and bay, are the chief timbers; along the streams, the foregoing together with palmetto.

Geology.

The geological formations of Florida include strata of Eocene, Miocene, Pliocene, post-Pliocene, and Recent periods. The present discussion will be limited to those directly involved in the geology of the phosphates.

Eocene. — The rocks of this formation are chiefly white, gray, or yellowish limestones, of porous, rotten, or marly texture, and highly fossiliferous. Their permeability to water renders them soft and

6 Preliminary Sketch Of The Phosphates Of Florida.

easily subject to disintegration, although exposed surfaces become hardened through atmospheric agencies. Siliceous bodies are dis- tributed throughout them. Their fossils comprise NummvMteSy Or bitMes, Echinoderms, and a host of molluscan forms. The thick- ness of the formation varies, but it has been penetrated at several points to depths between 300 and 600 feet without reaching the base. Alteration of the rocks has frequently resulted from the removal of some constituents and the acquirement of others, through the chemical agencies to which they have constantly been subjected. The distri- bution of the Eocene is approximately given on the accompanying map ; but the details of the outline, and of its relations to the forma- tions with which it comes in contact, are obscured by the deep mantle of recent sands and by the presence of innumerable swamps. Along the median portion of the Eocene area, with a north and south trend, lie the heavy deposits of hard-rock phosphates.

Miocene, — This formation embraces two clearly .defined and broad divisions ; an older and a younger. The former sttly'ls involved in the geology of the phosphates. Like the Eocene, it is essentially a limestone formation, but with the diiference that it is distinctly bedded and comprises rocks of a more compact nature, of greater hardness, and less subject to disintegration. The individual strata, about 4 or 5 feet thick, are frequently separated by softer zones of approxi- mately the same material, but more porous, and often marly in ap- pearance. Like the Eocene, this limestone contains siliceous bodies, and has, also, locally been altered to phosphate of lime of great richness. The original l>edded structure has been retained in the developed phosphate, which, unlike that of the Eocene area, is still frequently found in the undisturbed position of the limestone of which it is the altered product. The fossils include a most charac- teristic species of OrbitolUea, together with Hemicardium, Orthavlax, and numerous other molluscan forms. The Miocene is probably much thinner than the Eocene. Both the area of the formation and that of the phosphates are approximately given on the map, but the causes of obscurity in outline already noted for the Eocene, exist also in the present instance. The Miocene phosphate-area is confined to the northern and western part of the State. The formation directly overlies the Eocene, and, at several localities in northern Florida, is itself overlain by the red sands and clays of the Lafayette series.

Pliocene, — The several distinct phases of the Pliocene formation exhibited in southern Florida include marls, clays, and limestones, and a unique phosphate-deposit locally known as pebble-rock. The

Preliminary Sketc5H Of The Phosphates Of Florida. 7

latter possesses special interest as being directly the soarce of a most important class of phosphate. Its type-locality is on the headwaters of the Peace, Alalia, and Manatee rivers. It is in general an un- stratified bed of so-called pebbles of phosphate of lime, in a clay or arenaceous matrix. Both matrix and pebbles are, normally, white in color. The matrix is soft, friable, and pervious, permitting the free percolation of subterranean waters, and, when first mined, has a con- sistency that readily permits the separation of its contained pebbles by washing. Upon exposure to the atmosphere, the rock yields up its moisture and becomes hard and resistant. The base of the formation has been found in but few of the shallower pits ; in several places a depth of 30 feet has been reached in the deposit without attain- ing the bottom. Its thickness is, however, variable, the result of non-conformity, of transportation of its material by erosive action, and of causes connected with its mode of origin. The pebble- contents amount to about 40 per cent, of the deposit. The distri- bution of this deposit is not satisfactorily determined. The area of its type-locality, as at present known, is roughly outlined on the map; further developments may extend it a number of miles beyond these limits. Beyond the type-locality, an allied deposit, though perhaps of partially different origin, is found at various points along the eastern side of the Eocene belt, and in the northern part of the State, in the vicinity of Waldo and Stark, underlies a considerable area.

The age of this deposit has not yet been satisfactorily determined. Mr. W. H. Dall, of the United States Geological Survey, has pro- visionally assigned to it a positibn in the series of Florida Pliocenes, between an older and a younger member. Where observed by the writer it rests unconformably upon both Eocene and Miocene forma- tions. Its superficial relations to adjacent formations, however, remain obscure.

The clays and marls of the Pliocene are yellow or white, dis- tinctly stratified, and highly fossil iferous. In certain regions they carry layers through which phosphate grains and pebbles of a still different type from those just described are quite generally distributed. The productive area of these phosphate-bearing clays and marls seems, so far as at present determined, to be confined to the regions of the Peace and Caloosahatchee rivers and the streams entering the Gulf below Tampa. After the removal of the marly portions of these beds by chemical solution and mechanical action, their phosphatic material has become an increment to the gravel bars already in pro-

8 'Preliminary Sketch Of The Phosphates Of Florida.

cess of accumulation in the streams from abrasion of the pebble-rock underlying the watersheds. The thickness of Pliocene marls and clays is undetermined.

Eecent — The deposits of this age include the superficial sands; the bodies of sand and gravel occupying the early river-bed which now underlie the bottom-lands; and the sands and phosphatic gravels of the present channels.

The Structural Development of Florida. — Peninsular Florida, as already observed, is probably the emerged crest of an anticlinal fold that extends for several miles beneath the sea on either side. At the time of its first appearance above sea-level the Eocene area may have been peninsular, as at present, or insular. The early configuration of the fold has since been somewhat changed by dynamic influences, but more especially by the acquisition of later formations, which has always been to the east or south of the land already formed. Various formations have, from time to time, constituted the coast-lines of the peninsula, aflTording, with the deposits brought from the interior, a great variety of sediments out of which to build the strata of later date. The early building of the peninsula, perhaps accompanied by some oscillations and changes of level, continued to the close of Plio- cene times. At this point in its history, however, the entire area was again submerged to receive the mantle of superficial sands which to-day forms such a prominent feature of its surface. In the north- ern part of the State, the development has been more closely con- nected with the changes in level to which the main continental mass to the north has been subjected, and with the deposition of later formations, as, for instance, the Ifayette, the sediments of which were derived from the early Appalachians.

The Phosphates.

Florida contains four distinct and widely different classes of com- mercial phosphate, each having a peculiar genesis, a peculiar form of deposit, and chemical and physical properties that readily distin- guish it from any of the others. According to their mode of occur- rence, or some predominant characteristic, these classes have come to be known as "hard-rock" phosphate, "soft'' phosphate, "land- pebble " or " matrix-rock,'' and " river-pebble." Except the soft- phosphate, they underlie distinct regions, but a slight commingling of the material of one class with that of another is frequently observed. The remarkable variety of structure, texture and material thus pre- sented by the Florida phosphates affords evidence of complex chemi-

Pbeliminaby Sketch Of The Phosphates Op Florida. 9

co-mecbaDical processes in the formation of the deposits ; of difference in their manner of genesis; and of variation in the sediments held in suspension and in the soluble contents of the waters during their

Hard-Rock Phosphate,

Type-rock. — The type of this claas may be regarded as a hard, massive, close-textured, homogeneous, light-gray phosphate, showing larger or smaller irregular cavities, which are usually lined with sec- ondary, mammillary incrustations of. phosphate of lime. The frac- ture is angular or sub-conchoidal. The general appearance is that of a limestone deposited by precipitation from thermal springs, and, in texture structure, finds its counterpart in the pre-glacial lime- stone deposits of the Mammoth Hot Springs of the Yellowstone Na- tional Park. The incrustations of the cavities occur in all stages of development, from a single deposition to several layers in thickness. The cavities frequently contain also deposits of white, clay-like phosphate of lime, which may have resulted from partial solution and the attendant mechanical disintegration of the surrounding rock, or from like disintegration of more distant portions, the material from which has been brought within its present walls in suspension in percolating waters. After the deposition of this material upon the sides or floors of the cavities, the waters have receded, and the material has dried, cracked, and hardened even to rock-consistency. The contents of phosphoric anhydride ' (P2O5) in the type-rock run. slightly above or below 36.65 per cent.

Variations from the above type involve changes in color; in the- relative proportion of included space to the mass of the rock ; in the shape, distribution and nature of the cavities; in the sediments brought into the presence of the rock and laid down within its in- cluded spaces as secondary deposits ; in the mode of deposition of its constituents ; and in the subsequent alterations or mechanical changes which the phosphate has undergone. One or several of these variar tions may be encountered in the same specimen or body of rock.

Variation due to color, — From the light-gray or drab color of. the type-phosphate of this class, there are variations to a clear, white or deep brown ; to a series of whites, yellows, and buflFs in arock.of. a somewhat different nature; or to a blue or black which may show itself in a zone bordering the fissures, cavities, and the exteriors of those rocks which have been exposed to the action of wateF. This variety in color is due to the presence of either iron or organic matter.

10 Preliminary Sketch Of The Phosphates Of Florida.

or, it may be, of both. All phosphates coDtain a slight amount of iron, which analyses show to be quite uniformly distributed through- out the mass of the rock over the entire field. It is found alike in gray and brown phosphate, but not of necessity predominating in either. When it is prent in quantity, it is more frequently found in phosphate carrying secondary deposits of sand, either in the body of the rock or in its cavities, in which case it is associated with the sands. Coloring from organic matter has been little studied as yet. The apparent distribution of iron so often irrespective of color, indi- cates organic matter as a frequent and potent source of the latter.

Variation due to cavities, — The included spaces of hard-rock phos- phates impart a variety of structure widely divergent from the type, and at the same time afford certain evidence as to the mode of origin of the rock. The cavities appear to resolve themselves into three classes, according to their mode of origin. The first embraces cavi- ties irregular in shape, ranging from minute size up to 12 (but usually not over 3) inches in diameter, which have probably resulted from the solution of such portions of the original rook as were more readily attacked by carbonic and other acids carried in percolating waters. The second includes cavities considerably extenuated, sym- metrically disposed with reference to each other, in lines sometimes concentric, sometimes straight or slightly wavy and parallel, broken in continuity, and giving rise to an extreme type known as laminated rock. The direct gradation which may be traced from the close- textured, homogeneous, massive rock, established as the class-type, to one of completely laminated structure is of special interest. The observed transition and its resemblance to well-known parallels in other rocks, leave little doubt as to its origin, namely, either direct precipitation from a water-solution within a cavity or upon an ex- posed surface, or the replacement of carbonate of lime first deposited after the manner of calcareous tufa from thermal springs. Cavities of the third class are not frequently encountered, but may occur in great numbers within a comparatively small mass of rock. They are of two varieties : one, lenticular in shape, never over inch in length by or inch in thickness, resulting from the removal of a small nummulite characteristic of Eocene rocks ; the other much more attenuated, but resulting in like manner from another Eocene form, the Obitoides. In the Miocene phosphates evidences occasionally exist of the former presence of OrbitolUes. These forms are recog- nized in all stages of solution, disintegration, and removal; and the spaces left Jby them are often so numerous as to give the rock a honey-

Preliminary Sketch Op The Phosphates Of Florida. 11

combed appearance. They aflFord a direct key to the origin and age of this class of phosphates, namely, alteration-products of Eocene or Miocene limestones.

Variations due to secondary deposits, — In addition to the mam- millary incrustations lining the cavities of the primary rock, nearly all the rock-phosphates show still later secondary deposits of phos- phate of lime, lying within the incrustations, and filling the cavities completely or partially. This material may have become so hard- ened as to result in a composite rock which now shows a clean frac- ture across old and new portions alike. In the cavities partially filled, the material, — most probably a sediment, — is usually much softer, and exhibits cracks of contraction from the recession of the waters and the gradual evaporation of all moisture. It may be either pure white, as often in the more typical gray phosphates, or buff or yellow, as in the rock originally more highly colored ; in the latter case the material often shows upon fracture either an irregularly mottled appearance, or a disposition of the coloring matter in layers. Occasionally (and especially the case in the bedded, Miocene region) a secondary deposit is found upon what was originally the old sur- face of the rock. The texture of the secondary deposits is either that of fine clay, or a sand in a phosphatic cement, or a combination of the two. In either case, the deposit may be homogeneous in ap- pearance, or may show delicate though distinct lines of successive sedimentary deposition.

The age of the secondary deposits lies wholly within the Eocene and Miocene periods, the processes by which they were laid down continuing to the close of the latter. Interruptions to sedimentation, indeed, occasionally took place, to be again resumed as the conditions became more favorable. Evidence in support of the foregoing exists on all sides, in the size of the cavities, in the various stages of solu- tion and disintegration, in the character of the mammillary incrusta- tions, in the distinct lines of deposition, and in the occasional pres- ence of even two periods of incrustation.

In regard to the origin of the secondary deposits, it is possible that in some instances it may be found in precipitation, but present information generally points to deposition of suspended matter from quiet water. In all the cavities of the hard-rock phosphate as seen to-day there are comparatively recent deposits of white sand and purple clay. There is no question as to its manner of deposition, and the hypothesis of like mechanical sediments at the time of the early formation of the secondary phosphate in the cavities of the older rock is quite admissible.

12 Preliminary Sketch Of The Phosphates Op Florida.

VarioMona resulting fromfrcmo7i8, — These are two : one, a breccia ; the other, a product of disintegration.

The brecciated variety is evidently the result of a re-cementing by phosphatic material of the fragments of a hard-rock phosphate, or else the alteration to a phosphate of an earlier, brecciated limestone in which there has been a pseudo-morphic deposition of th&phosphate after the shape of the older fragments. This variety of rock is not of general occurrence, although found at several localities in the hard-rock belt.

Disintegration of the hard-rock in various stages of progress is frequently encountered. The process may have bpen conducted with homogeneous effect throughout the entire body of a rock ; it may form a zone upon the exterior; or upon breaking open the rock, va- rious portions may be found softened and ready to be removed if once reached by percolating waters. A large body of hard rock may have been thus disintegrated into a mass consisting partly of fine angular fragments, partly of a soft impalpable material, the extreme of the action. Through the latter the hard-rock passes into the variety locally known as soft phosphate. A distinction, however, is to be made between these two varieties on account of the lower com- mercial value of the finer, or soft phosphate proper, which contains a lower amount of phosphate of lime and a higher percentage of iron and alumina. At several of the mines this point has been recog- nized, and the material has been designated as No. 1,' 2," or " 3 " fine, or as softs " and " fines." The fine angular matter is, in reality, precisely similar, chemically and physically, to the large un- altered rock-masses. The disintegration of this class of rock has probably occurred since Eocene times.

Fossils of the Aard-ocZ:.-— The phosphate of this class does not generally C/ontain fossils, but casts or impressions of them are not in- frequently met with. The fossils vary according as the original rock from which the phosphate has been derived was of Eocene or Mio- cene age.

Soft Phosphates.

The name "soft phosphate" has been arbitrarily given to a class of material occurring in connection with the hard-rock phosphate over the entire region in which the latter is found. In general usage, it designates anything phosphatic that is not distinctly hard rock, including, on the one hand, the material resulting from the disinte- gration of the hard rock, and, on the other, highly phosphatic clays

Preliminary Sketch Op The Phosphates Op Florida. 13

and sands. At times it has even been applied to the pebble-deposits of the next class. Under this broad use of the term, it is evident that the quality of the soflb phosphates must be very variable, chemi- cal analyses showing marked differences in their contents of phos- phajte of lime, iron, and alumina. There are thus several grades of soft phosphate, the purest of which is the homogeneous and clean product of alteration from hard rock. The quality of the other grades varies according to the amount of sand and clay either con- tained in the original rock or mingled with the phosphate in the process of re-deposition. This material, together with the disinte- gration-product of the hard rock, forms, by reason of its general dis- tribution, and the but partially successful attempts thus fer to employ it in the manufacture of fertilizers, one of the most serious problems of the economic working of the hard-rock deposits.

The phosphoric anhydride (P2O5) rarely averages 22.90 per cent, of the mass.

Land-Pebble Phosphate.

The pebbles constituting this class vary in size and shape, but are normally of uniform texture, color, and chemical contents. They are white, but when subjectekl to percolating or stream-waters, be- come dark gray or almost black. The exterS>r is smooth and glossy, and there is a thin outer zone of closer texture and greater density than the average for the entire pebble. The pebbles are composed either of an earthy material carrying fossil remains, grains of quartz, and pisolitic grains of lime phosphate, or else of a material resem- bling in texture and appearance the yellow, white, or gray varieties of hard-rock phosphate. They range from minute size to that of an English walnut. The fossils observed in them have not been suffi- cient for the determination of their age, and consequently are insuffi- cient for inference as to their derivation.

The phosphoric anhydride (PjOg) averages about 32.06 per cent.

River-Pebble Phosphate.

The designation " river-pebble " is based on the usual manner of occurrence of this class of phosphate. The type, however, is found not only in the rivers of to-day, but also in the broad deposits filling their ancient channels, in coastal sands, and, again, in certain hum- mock-lands, as on the upper Caloosahatchee river. Along Peace river, where it has been most studied, it occurs in bars in both the present and ancient river-channel, into which it has been washed

14 Preliminary Sketch Op The Phosphates Of Florida.

from the bordering beds of clay and marl on either side, and from the land-pebble deposits which underlie the water-shed. The pebbles are blue, black, or dark gray outside, gray or yellowish-brown inside, and range up to an inch in diameter. In internal structure they are close-textured and homogeneous, but not infrequently cavities occur in them, the result of chemical solution, or, more rarely, of the disappearance of fossil remains. With the pebbles are associated remnants of bone and teeth of various animals and the phosphatized casts of shells, the latter being particularly a feature of the Caloosa- hatchee deposits, fully 60 percent, of the phosphate of which is thus constituted. The shell-casts show a slight amount of attrition, but in many cases their original form, even to the beaks of bivalves and the markings of univalves, is distinctly preserved. The exterior and interior color of the casts and bones are the same as of the peb- bles proper. The internal structure of the bones, however, has usually been fairly preserved. In the stream deposits of western Florida bones of all sizes occur, constituting the bulk of the de-

y&OSltS.

The Caloosahatchee pebble is largely mixed with the white (car- bonate of lime) remains of Pliocene and post-Pliocene shells, de- rived from beds which border the stream for its entire length. Sand and clay are also found with the pebbles, but the shells serve at once as a distinguishing feature, these being almost -wholly absent from the deposits of the other streams.

The pebbles of Black creek, which enters the St. Johns from the west, about 20 miles south of Jacksonville, somewhat resemble those of Peace river, but are lighter in exterior color, being usually a light brown.

The deposits of the Withlacoochee river are, for the most part, derived from the hard-rock phosphate through which the river has cut its course. They differ from the rock of the land only in the black color imparted by the action of water. With the river de- posits of the Withlacoochee also, are found bones of large anins in great abundance.

The Peace river pebbles average in phosphoric anhydride (P2O5) about 28.40 per cent.; the Black creek, 20.61 per cent.

The Deposits.

Hard-Rock g w d ' i ff i Phosphate,

Eocene area, — The deposits of this classt in the Eocene area lie in a narrow median belt, approximately 150 miles in length, roughly

Preliminary Sketch Op The Phosphates Of Florida. 15

parallel to the present Gulf coast, at a distance of between 25 and 50 miles, according to the sinuosities of the latter. Essentially, the hard-rock phosphate occurs as a boulder-deposit in a soft matrix of phosphatic sands, clays, and other material resulting from the disintegration of the hard-rock aud i iSnmiSm the soft phosphates. The component materials lie in the utmost confusion, the only ap- proach to order being a division into superficial sands, containing little hard-rock or other phosphate, and the boulder-formation proper, with its associated matrix, which immediately underlies these sands, an uneven line of non-conformity existing between the two. The greatest depth yet reached in the formation is about 60 feet, but the thickness of the deposit will naturally vary from point to point.

The mantle of superficial sands is also variable, between a few inches and 20 feet, the depth generally being under 10 feet. The sands are light or rusty brown, and consist of quartz grains of medium coarseness loosely held together in a ferruginous cement ; they are very uniform in composition, and exhibit no stratification or other lines of deposition. Not infrequently boulders of hard-rock have been included in the sand, but they are generally only the upper members of the deposit below, from around which the older material has been carried away. The base of the superficial sands is a wavy plane ; its line of demarkation from the material below may be either distinct or there may be a gradation in color and phosphatic contents from the one deposit to the other.

The phosphate-deposit proper is white. The boulders are of irregular though somewhat rounded outline, vary in diameter from 2 or 3 inches to 8 or 10 feet, lie imbedded in all positions, and are encountered, singly or in groups, to the greatest depths yet attained. A recent pit on the Dunnellon property showed an irregularly py- ramidal accumulation of them which was, so far as uncovered, 30 feet high, 100 long, and 40 wide. Every form of assemblage is encountered, and it is this feature that causes iso great a variation in the cost of mining. Boulders of every lithological variety, massive, laminated, intermediate, or in the various stages of disintegration, are found at all points. Besides the soft phosphate proper, the material of which the matrix of the deposit is composed includes a white quartz sand, the grains of which are more or less strongly held together by a white phosphatic cement, and a clay, usually drab, but not infre- quently blue, green, white, or orange, which occurs in large irregular bodies in the midst of the other members of the deposit, or com- pletely surrounds the individual boulders. Both sand and clay con-

16 Preliminary Sketch Op The Phosphates Op Florida.

tain more or less phosphate of lime in finer particles, resulting from a general distribution of the disintegrated portions of the boulders during deposition. At the same time there was also in suspension in the waters a still finer sediment which silted out with these mate- rials, rendering the clays themselves often highly phosphatic, and forming between the grains of sand the cement holding them to- gether. The bodies of clay occasionally show a trace of lamination more distinctly marked in some localities than in others. These sands and clays have become lodged in the pores and cavities of the hard rock, and form a considerable portion of its impurities. Fine crushing is required to liberate the sand completely, while even this means, with calcination added, will not free the rock from the clay. It is probable that washing will sooner or later be added to the methods already in use, for the treatment of at least a portion of the mined product.

The line between the true phosphate-deposit and the superficial sands is often marked with more or less hard-rock gravel, derived from the boulders below, the pieces generally showing a certain amount of wear from having been rolled about. This gravel is of universal distribution, but varies in amount from point to point.

Throughout the hard-rock deposits of the Eocene area none of the hard-rock has been found in its original position. By the side of the phosphate boulders in the same pit may occur others, siliceous or of limestone. So far in depth as explorations have reached, this condition prevails, and it is doubtful if any other exists above water-level, which is now but little below some of the deeper pits.

The distribution of the rock-phosphates of the Eocene area is irregular. In some localities heavy deposits exist, while in others there may be none at all. The extent of those portions of the belt thus far yielding to the prospector no evidence of phosphates, it is impossible to conjecture. While a general examination has been made of the entire area, the lines of productive and unproductive areas have been established in but few instances. The southern limit of the Eocene belt is in the vicinity of Richland, in Pasco county. From this point it follows the course of the Withlacoochee river, lying generally to the west of the stream, until, at Dunnellon, where the river turns sharply to the west, the deposits cross it and hold their course with slight deviation to the vicinity of Fort White and Ichetucknee, whence the belt turns westward, and ap- pears finally productive in the vicinity of Luraville on the Suwanee river.

Preliminary Sketch Of The Phosphates Op Florida. 17

Miocene area. — While the hard-rock phosphate of this area closely resembles that of the Eocene in its lithological characteris- tics, there are several important differences in its manner of occur- rence. Chief among these are : the position of the hard rock in aUu in several localities, the bedded character of the deposit/ and the absence of soft phosphate. These featjlres are largely due to the differences between the original strata of the Miocene and Eocene ages, which have been the sources of their respective phosphates. Further differences are due to the genesis of the deposits. The same process of phosphatization has been carried on in the Miocene area as'in the Eocene, but the breaking pp and re-sorting of the mate- rials, so complete in the latter area, has not been carried so far in the former. The hard-rock in the Miocene area is, indeed, found as boulders in the deposits of sand, but there are many localities be- neath which the rock still exists as an undisturbed bed.

The country underlain by this phosphate is of the low, flat-woods type. The beds lie horizontal a few feet beneath the surface, cov- ered only by the superficial sand, which, in the boulder-deposits, more or less completely surrounds the rock. The thickness of the bed in situ is probably rarely over 10 feet, and usually only 4 or 5. The phosphate is an alteration-product of an earlier limestone, and as such is subject to the original variation in thickness from point to point. The underlying stratum, in the one or two possible instances where the rock in situ has been pierced, is a clay, but observations in this particular were unsatisfactory. In the boulder-deposits the order of succession is : at the surface, superficial sands from 1 to 7 feet deep, carrying most of the phosphate-rock ; beneath these, a white quartz sand, the grains of which are held together with a white phosphatic cement, a foot or two in thickness where observed, . but at times absent. This is underlain by yellow, blue, buff, or white clay, apparently only slightly phosphatic.

The absence of the soft phasphates in the Miocene area is note- worthy, and indicates not only a dree of attrition and later chemi- . cal action considerably less than took place in the Eocene area, but perhaps also different topographical details as well.

The phosphate-beds of the Miocene area, boulder, or otherwise, extend from the base of the prominent bluffs of the Lafayette forma- tion southward beneath the flat-woods country for an undetermined distance. Their continuity for more than a mile is doubtful ; un- altered and siliceous bodies frequently occur, indicative of interrup- tion similar to that in the Eocene area.

18 Preliminary Sketch Op The Phosphates Of Florida-

Land' Pebble Depodta.

The general character of these deposits has already been given. Their origin will be discussed below. Further consideration at this point is, therefore, iMt necessary.

River-Pebble Deposits.

The character of these deposits has been given in a general way in describing the lithological features of the pebbles. The type-form occurs more particularly in the Peace, Caloosahatchee, Alafia, and other rivers entering the Gulf south of Tampa and Hillsborough bays. The rivers to the north — the Withlacoochee, Aucilla, and those of western Florida — carry a mixture of pebbles, hard-rock fragments, and bones, according to the strata through which they flow. The bars of Peace river are more extensive than those of other streams, owing to the greater area drained, and the consequent greater supply of material. They vary as in all rivers, in the quan tity of material, and shift from point to point with the change of currents from whatever cause. The position of the bars is usually in the slack water below the convexities of the stream-channel al- though, in the case of heavier deposits, they may accumulate over the entire width of the river-bed.

Origin of the Phosphates.

Introductory. — In presenting the following views upon the origin of Florida phosphates, the privilege of subsequent modification is reserved as data bearing upon the question become more complete. The evidence derived from the lithological varieties of phosphates, and from the differences in their manner of deposition, points to a diversified origin and method of development, in which a number of agencies have acted either synchronously, or independently yet with influence one upon another. The essential factors in the origin of the rock-phosphate are : phosphate of lime ; carbonate of lime, either as limestone or as highly calcareous marl; a reagent, in the presence of which both phosphate and carbonate of lime are soluble ; and water as a carrying agent.

The origin of phosphate of lime in sedimentary rocks is unknown. Its presence in sea- water ; its broad distribution in both plant and animal life ; its occurrence in rocks of all ages, even to the extent of economic value ; and its special presence in limestones, more par- tioularly Cretaceous and Tertiary limestones, are facts long recog-

Preliminaky Sketch Of The Phosphates Of Florida. 19

Dized. Ite occurrence in receirt time in the form of leached and soluble guanos on many of the oceanic islands and the phospbatiza- tion of the underlying strata, have also been noted by many authori- ties. The last is by actual observation a tangible source, but the features first detailed point to some other and more general origin of phosphate of lime than localized bird-deposits, or the but littk more widely distributed accumulations of animal remains. Its presence in sea-water, after the manner of carbonate of lime, though in far smaller amount, is well established ; both materials are of general occurrence, and each play a prominent part in sea-life. The transfer of a considerable percentage of phosphate of lime to localities having conditions favorable for its deposition, either in sediments then set- tling or on surfaces of rocks already laid down, has doubtless been accomplished in many cases through the instrumentality of animals secreting it. Oceanic currents may have assisted this accumulation. Again, southern waters, swamps, and lands give evidence of the presence in them of abundant life, secreting phosphate of lime and afterwards returning it to the beds on which this life rests, A study of the phosphates of the world points, in certain cases (as, for in- stance, in the general presence of lime phosphate throughout a thick series of strata), to the oceanic origin of this mineral, while in other cases it points with equal force to a local origin, from guano- deposits and the accumulation of animal matter. The evident sec- ondary transfer of phosphate of lime as a silt has not been con- sidered.

The solvent power of carbonated waters upon limestones and marls is well known. Its increased effect upon these rocks in pro- portion to their porosity and the amount of exposed molecular sur- face is also recognized. The Eocene limestones of Florida are ex- tremely porous. Moreover, the waters of Florida are now, and probably have been since the first emergence of the peninsula, heavily charged with carbonic acid. The quantity of carbonic acid in the off-shore waters in various parts of the world is given by Bischof at five times the amount required by the carbonate of lime held in solution. This disparity probably becomes still greater in the highly- charged waters of the land. The solvent power of the waters of Florida is therefore ample, not only for the removal of large amounts of carbonate of lime, but for taking up considerable quantities of phosphate of lime as well.

The following table, published in Bischors Chemical Geology, gives the solubility of phosphate of lime in saturated carbonated water.

20 Preliminary Sketch Op The Phosphates Op Plorida.

Apatite dissolves in,

Apatite, after brisk agitation with the liquid, in, Artificial neutral phosphate, freshly precipitated, in Same salt, after thorough drying in air, in, . Artificial basic phosphate, freshly precipitated, in, Same salt, after thorough drying in air, in, .

Same salt, after ignition, in,

Burnt bones which had been exposed for several years, and

had absorbed carbonic acid, Fresh ox bones, in shavings,

Fossil bones that had been buried at least thirty years,

Water saturated

with COa,

parts.

393,000

96,670

1,503

2,042

1,102

5,432

13,115

2,823

4,610

f 6,400

13,300

In reference to this table Bischof says: "These results show how remarkably the solubility of phosphate of lime varies according to its source, and the kind of admixtures present/'

With regard to the solubility of bone he adds: "The quantity of carbonic acid requisite for the solution of bones is by no means large, and in situations where carbonic acid is copiously and con- tinuously evolved in putrefaction, their solution may take place rapidly."

And again : " It is deserving of notice that basic phosphate of lime dissolves in 3150 parts of water, containing onetwelflh of its weight of chloride of sodium. The presence of chloride of ammo- nium increases the solubility still more. Now, since chloride of sodium is so frequently present in water, its solvent relation to phos- phate of lime will be proportionately greater,"

Genesis of the hard-rook and soft phosphates, — The development of these deposits is divisible into three periods : First, that in which the primary rock was formed ; second, that of secondary deposition in the cavities of the primary rock (excluding recent sands and clays) ; third, that in which the deposits thus formed were broken up and the resulting fragments and comminuted material were re-deposited as they now occur.

The first of these stages probably began not later than the close of the older Miocene, and within the Eocene area it may have beg|in much earlier. Whether the primary phosphate resulted from a su- perficial and heavy deposit of soluble guanos, covering the limestones, or from the concentration of phosphate of lime already widely and uniformly distributed throughout the mass of the original rock, or from both, is a diflScult question. In any event, the evidence indi-

Pbeliminaby Sketch Of The Phosphates Of Florida. 21

cates the effect of the percolation of sarface-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 re- deposited under conditions favorable to its separation. Such condi- tions 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 concen- tration, 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 por- tions of the deposit.

The thickness of the zone of phosphatization in the Eocene area is unknown, but it is doubtful if it was over 20 feet. In the Miocene area the depth has been proved from the phosphates in sUu to have been between 6 and 12 feet.

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. An interesting and suggestive fact in this connection is, that precise duplicates of the structure of the primary phosphates may be ibund in the carbonate of lime deposits of both post- and pre-Glacial times in the region of the Mammoth Hot Springs in the Yellowstone Park.* Every form from the laminated variety through the semi- compact or compact-laminated to the massive, may be found in both deposits.

Deposition taking place by chemical precipitation on free surfaces after the manner suggested above, might have occurred, according to circumstances, either on a surface exposed to the atmosphere or on that of an interior cavity. In the latter case, by continued growth the cavity would become filled with laminated or massive rock, which, upon solution of the surrounding material or the complete breaking down of the formation, as in later times, would result in a rounded

For a full description of the carbonate of lime deposits of the Yellowstone Na- tional Park, see the article by W. H. Weed on the " Formations of Travertine, etc./' in the Ninth Annual Report of the Director of the United States Geological Survey.

22 Preliminary Sketch Op The Phosphates Op Florida.

body of phosphate of lime resembling a sea-rolled boulder. Both to this method of origin and to the attrition which the fragments proper suffered, are probably due the forms of the hard-rock phosphate of the present deposits. Another method of deposition of laminated rock might be found in the continued washing of a coast-outcrop by the sea, each wave that dashed over its surface leaving behind a slight amount of phosphate of lime precipitated by the loss of the solvent carbonic acid through aeration.

Of the deposits of secondary origin in the interstices of the primary rock, it is clearly evident that many were due to actual sedimenta- tion. It is quite possible that others, particularly the homogeneous, white variety, may have been due to precipitation from water still percolating the phosphate first formed. The process of secondary deposition must have been periodically or continually kept up for a long period, until some definite climatic or geologic change brought about conditions no longer favorable to it. In addition to action of this nature, we may mention the fracturing of rock already phos- phatized and the recementing of its parts by material equally pure, resulting in the brecciated variety occasionally encountered.

The deposits of phosphate thus formed in the Eocene and Mio- cene times of the Florida peninsula were remarkably free from iron and alumina, in comparison with many of those in the West Indies. The original percentage may have been somewhat reduced in the process of rock-formation, but at no time could ther have been such large proportions as are found, for instance, in the Navassa rocks.

The third period in the genesis of the hard-rock deposits includes the destruction of the original beds and the piling up of their result- ing boulders as they are found to day. The time is uncertain, but it may have been during the last submergence of the peninsula, when the conditions would have been extremely favorable for the solution and abrasion of the limestone lying beneath the phosphatized zone. This limestone is everywhere of a comparatively soft and friable nature, and upon exposure to climatic or aqueous forces would readily yield. The support being thus removed, the overlying beds would be broken, washed, and rolled into rounded fragments, and their interstices still further filled with the materials, — sands, clays, and soft phosphates, — naturally held in suspension in the waters. The distance which the boulders have been removed from the origi- nal bed is probably slight.

The material in which the boulders are now found was derived

Pkeliminary Sketch Op The Phosphates Of Florida. 23

from various sources. The sea-sands and clays, in whole or in part were probably brought by currents, the former being receraented with the fine phosphatic sediment held in suspension ; a portion of the hard-rock was comminuted, either retaining the shape of the original boulder or being completely destroyed and carried away in fine fragments, to be included among the sands and clays of syn- chronous deposition. . The general distribution of the fine, impalpa- ble soft phosphate throughout the deposit is accounted for by the enormous amount of sediment of that nature held in suspension.

Genesis of the land-pebble phosphate, — The resemblances in tex- ture, color, fossil casts, and general appearance which the pebbles of this deposit occasionally bear to the hard-rock type are in a measure suggestive of their derivation from a limestone of pre-Pliooene times, possibly older Miocene. On the other hand the prevailing white color, the often earthy appearance of the frash surfaces, the lower percentage in phosphate of lime, the softness and the condi- tion of preservation of included fossils suggest their origin from a marl or at least a very earthy friable limestone. In either case they may be the rolled fragments of pre-existing beds, a possibility enhanced by the character of their matrix and by the occasional presence of well rounded, white quartz pebbles.

Prof, N. S. Shaler, in an unpublished paper on " Residual Abla- tion Deposits" places the land-pebble phosphates in this category. According to this experienced observer, the circumstances which favor the development of residual deposits containing a larg.e amount of lime phosphate appear to be substantially as follows l

" It is in the first place necessary to have thick beds of limestone more than.usu ally rich in phosphate matter. These beds must not be of too dense- a nature for it is important that they should permit the soil waters to penetrate into- their depths, and thereby accomplish their appropriate leaching action. The rainfall of the dis- trict in question must be considerable in order to supply a large vx)}ume of percolat- ing water and incidentally to maintain the soil bed rich in decaying vegetable -mat- ter by which the rain waters are given tlieir solvent power. This assemblage of conditions rarely occurs. So far as my knowledge goes, it is only found; on an ex.- tensive scale in the southeasternmost portion of the United States where the lime- stone marls of Tertiary and Cretaceous age have in recent geological period8,.and particularly daring the portions of those ages when the region stood much higheri above the level of the sea than at present been exposed to great leaching action.

''The best conditions for the accumulations of valuable deposits of lime -phosphate in residual dibris appear to occur where the phosphatic lime marls are of a rather soft character; the separate beds having no such solidity as will resist theperoola- tion of water along innumerable incipient joints such as commonly pervade strati-

21 Preliminary Sketch Of The Phosphates Of Florida.

fied materials, even when they are of a very soft nature. Passing downward through such a deposit the effect appears to be to remove nearly all the lime car- bonate and to leave the lime phosphate in the form of sub-angular or pebbly bits. In their first state these fragments of concentrated matter appear to have had their form to a certain extent determined by some natural fractures of the rook which appear to have been essentially joint planes. On the surfaces of these fragments there appears to have been in cases, perhaps even generally, a certain amount of concretionary deposition. The result is that the fragments of pebble phosphates generally have smooth surfaces which often indeed have an almost polbhed char- acter. The fact should be noted that these fragments have necessarily been sub- jected to more or less attrition of bit against bit, as is the case with all residual de- posits of this nature. It is evident that the process of concentration, such as I assume to have taken place could not be accomplished without a greater amount of interstitial movement and consequent friction of fragment upon fragment.

"In the case of the pebble phosphates it is evident that the fragments have been to a certain extent swept from the uplands into the valleys. Thus on the low di- vides between the Alafia river district and the neighboring portions of Florida, the phosphatic pebbles may form but a thin layer or be altogether wanting, while in the valleys the accumulations of pebbly material may have a thickness of 30 feet or more. This segregative process has probably in part been accomplished by the work of the streams themselves, but is in my opinion mainly due to the action of the sea during the time or times when this part of the peninsula has sunk be- neath and risen above the ocean level. The action of the sea in this concentrative work appears to be indicated by the frequent occurrence of shark's teeth, and other remains of marine forms in a state of preservation which seems to me to clearly in- dicate that they were formed since the phosphatic pebbles took their shape. They appear indeed to be mere accidental and exceedingly modern elements of the de- posit They have evidently experienced no sueh attrition as has affected the pebbles . themselves."

Of the above suggestions, that of Prof. Shaler perhaps most nearly satisfies the various facts.

The original deposit, of which the present one is the residual por- tion may have been formed from sediments derived from the older phosphatedeposits. These sediments must have settled out as a phosphatic mud, the phosphate of lime in suspension being deposited with the silt and segregating itself into the portions of the deposit, subsequently becoming pebbles. Oolitic grains are not infrequently found together with fossils and sand distributed within the mass of the individual pebbles.

The deposits of pebble, plate-rock, and soft phosphate east of tha Eocene area, are regarded as nearly equivalent in age to the land- pebble beds of south Florida. The growth of peninsular Florida since Eocene times has chiefly been eastward ; and it may be in- ferred from the materials constituting the strata, that the surface- slopes and drainage have also been chiefly in this direction. Hence, it is on the eastern side of the rock-phosphate belt that the sediments

Pkbliminaky Sketch Op The Phosphates Of Florida. 26

derived from it, and the materials carried in actual solution have again been deposited in the hollows of the older limestones, in well- developed beds of individual character. These deposits are hetero- geneous in the nature and distribution of their materials, brought about by erosion and solution of the underlying limestone, by the filling of the hollows with materials from divers sources, and by the breaking up of the already deposited layers of plate-rock, itself the result of sedimentation from successive flows of a fine silt.

Genesis of the river-pebble phosphate. — The origin of the river- pebble itself was doubtless somewhat similar to that of the land- pebble, that is, from a previous highly phosphatized marl, either directly as pebbles and shell-casts, or by segregation of the contained phosphate of lime in nodules and shell-casts, and the subsequent leaching out of the carbonate, which set nodules and casts free, and, according to the locality in which it took place, whether hummock- land or stream-channel, permitted their accumulation as a superficial layer just beneath the soil, or as bars in the rivers.

Variation of the several classes of phosphaUs in their phosphate of lime contents. — This may be explained on two grounds. In the first place, the original material of which the phosphates are alteration- products was a limestone or a marl, the hard-rock, perhaps, being derived from the former, the two classes of pebble-phosphates from the latter. The carbonate of lime in natural limestones and marls often varies considerably in quantity. The phosphate of lime would occur in the alteration-product in proportion to the amount of carbon- ate of lime available for replacement in the original. In phosphatized nearly pure limestones, the phosphate of lime would reach a corre- spondingly high percentage ; in marls, on the other hand, in which the percentage of lime is often low, the resulting phosphate would be correspondingly diminished. If now the phosphate of lime tend 7 to form segregations and the balance of the respective beds is ' away, the remaining phosphatic materials must vary in their phos- phate of lime contents in proportion to the carbonate of lime of the original rock-mass.

The second explanation of such differences in phosphate of lime contents was suggested by Shaler, and lies in the solubility of this material in waters containing carbonic acid and the greater length of time during which one class, as for instance the river-pebble, has been subjected to solvent action as compared with another class, such as the land-pebble. Either explanation will satisfy the conditions, and it is not improbable that in many instances both are applicable.

26 preliminary sketch of the phosphates op florida.

Chemical Constitution op the Phosphates.*

The accompanying analyses have been selected with a view to studying the relation between chemical constitution and physical ap- pearance in the various phosphates. They are not, therefore, to be regarded as representative of the general run of the rock of the mines from which they came, either in phosphate of lime, iron, alumina, or insoluble matter. The analyses given include numerous variations of the hard-rock type and typical specimens of the land- and river- pebble classes. Two series of special observations, Nos. 74 and 97, made upon sandy varieties of the first type, will afford an idea of the distribution of the insoluble and other undesirable constituents throughout the rock-mass. The constituents determining the rela- tive values of phosphates are phosphoric anhydride (P2O5), the oxides of iron and alumina (FegOg, AI2O3), carbonic acid (COg), and the insoluble matter. These will be considered according to the classes of phosphate.

Hard-rock phosphates. — The contents of this class in P3O5 range within a few per cent, on either side of 36.65, corresponding in com- mercial language to 80.00 per cent, of the tricalcic phosphate (CagPgOg). The percentage of PgOg is generally in inverse ratio to the amount of insoluble matter, chiefly sand. The P2O5 in these analyses ranges from 32.68 (71.34 CaaPjOg) in No. 87 to 38.84 (84.79 Ca3P208) in No. 96. The insoluble master ranges from 8.78 in the former to 0.49 in the latter; but in th connection it is to be re- marked that slight variations in either insoluble matter or phos- phoric anhydride — as, for instance, 0.05 insoluble matter in a phos- phate carrying 57.76 PgOg (82.43 CajPaOg)— are frequent, and are not to be regarded as affecting the general law.

The combinations into which P2O5 enters in the phosphates of Florida are, in the order of preference, those with lime, alumina, and iron. In the varieties which closely approach the type-rock of the class, its combination with alumina and iron is at a minimum. At the other extreme, however, where either sand or clay plays a conspicuous part, a considerable percentage of the P2O5 is combined with iron and alumina. This is also the case in soft phosphates, illustrated by No. 98. The last might indeed be regarded a phos- phate of lime, alumina, and iron, into which, however, iron prob- ably enters in but slight amount. The combined lime (CaO) and

The chemical analyses accompanying this paper have been made by Dr. T. M. Chatard, of the Division of Chemistry, U. S. Geological Survey.

I>Reliminary Sketch Of The Phosphates Of Florida. 27

magnesia (MgO) contents in the hard-rock class of phosphates vary in a general way directly as the contents in PjOg. In No. 63, how- ever, the higher percentage of CaO with even a lower proportion of P2O5 is accounted for by the amoant of CO2 present.

It is sometimes the case that when a phosphate contains a large proportion of insoluble matter, the contents in alumina and iron (but chiefly the former) are considerably increased. This is a natural feature of deposition, for in the broad study of the deposits it is almost everywhere observed that when sands have been brought to the deposit, clays have likewise settled out of the waters of sedimen- tation. In the phosphates in which such matters are included in the mass of the rock, the sands alone appear to the eye, the clay being indistinguishable.

Under slightly different conditions the foreign sediments might easily have predominated in clay, in which case such analyses as Nos. 42, 96, and 99 would result, while in the soft phosphate, as illustrated in No. 98, the high percentage of alumina has long been recognized.

The insoluble portion of the hard-rock phosphates is chiefly sand, in the form of rounded, white, transparent quartz grains. A pre- liminary knowledge of the relative amounts as determined by chem- ical analyses in rock of varying appearance, affords the engineer a rough estimate of the comparative value of specimens submitted for inspection. As an extreme instance in insoluble contents, sample No. 97 is cited, which is in reality a phosphatic sand, a type fre- quently met with in the hard-rock field, especially associated with the soft phosphate, and often regarded as valuable by those owning property. An inspection of the analysis renders intelligible its characteristics and its present value.

Carbonic acid in the hard rock is indicative of the percentage of carbonate of lime. The amount occurring in No. 63, an analysis of the secondary incrustations in a specimen conspicuous for bearing a formation of this kind, is worthy of notice. It should be added, however, that it was impossible to completely separate the incrusta- tion from the underlying portion of the rock.

The fluorine, which universally occurs as a constituent of Florida phosphates, is of both scientific and practical importance ; but the investigations concerning it, conducted by Dr. Chatard, are in their incipiency, and will not now permit a statement as to the geological or economic bearing of the mineral.

The deteriorating constituents of all phosphates are chiefly the in-

28 Preliminary Sketch Of The Phosphates Op Florida.

soluble matters, the carbonate of lime, and the oxides of iron and alaraina. Of these, the first, in reasonable amount, is of least importance, since its effect is chiefly mechanical, adding by its weight to the cost of transportation and handling. The second constituent, carbonate of lime, has in addition a chemical disability in that it takes up a certain amount of sulphuric acid in the manu- facture of superphosphates, thus adding to the cost of materials em- ployed in that process. The remaining deteriorants of importance contained in natural phosphates are the oxides of iron and alumina. The effect of these is manifold, but the chief objections are their tendency, first, to cause an acid phosphate to revert, with a direct loss of P2O5, and secondly, to render the manufactured product moist and sticky, and difficult, if not impossible, to dry. Phosphate buyers therefore usually limit the contents in Al2(Fe2)03 to 4 per cent., deducting for each unit of these constituents above this per- centage, the equivalent in phosphate of lime which might become available from the P2O5 taken up by the Fe2(Al2)03.

There are among the samples of hard-rock and soft phosphate four, of which the analyses have been conducted with special refer- ence to the study of the distribution of their deleterious constituents. These are Nos. 74, 87, 97, and 100, of which Nos. 74 and 97 have been subjected to the most extended study, the results there obtained being duplicated in Nos. 87 and 100, up to the point to which the investigations were carried. The studies, of which some of the typi- cal results are given in the analyses, were suggested to Dr. T. M. Chatard and myself during a visit in company to the hard-rock regions of Florida. The investigations, the results of which are given in the table of analyses were wholly conducted by Dr. Cha- tard, and are described in his paper presented at this meeting, on Phosphate Chemistry as it concerns the Miner.

The land'pebbk. — The analyses given of this class of phosphates although but two in number, 937 A and 940, may be regarded as typical, and, at the same time, in the variations in the amount of their several constituents, especially their phosphoric anhydride, as representing the limits of the rock at the two ends of the series of gradations. The most usual percentage of phosphate of lime is between 68 and 70, but not infrequently the class is found to approach the lower members of the hard-rock series, and the higher ones of the river-pebble class. The line between the three classes in this particular is, however, distinct, — quite as distinct, in fact, as their differences in physical appearance.

I*Reliminary Sketch Of The Phosphates Of Florida. 29

A %

Their lime (CaO) jcontents also generally falls below the percen- tage of this constituent in the hard-rock. Their other contents do not need special mention at this time.

Analysis No. 937 B represents the matrix which held the pebble affording 937 A. The matrix was sandy, but this is a highly vari- able feature. Its phosphate of lime contents are in part the result of fine material similar in character to the pebbles themselves, but lich it was not intended to separate, the general run of the matrix, representing the tailings in washing on a working scale, being de- sired. It is probably representative of the lowest percentage to which it will pay to dress, wash, and separate the two components of the deposit, the pebble and matrix. Its percentage of alumina and iron, more especially of the former, is high ; this seems to be the case in all phosphates of a soft material whether of the hard-rock or the other areas. The water contents of this sample are high on account of a washing to which the original material was subjected for re- moval of the pebble of 937 A from the matrix. Preliminary drying was not carried to the degree it might have been.

The river-pebble. — The chemical constitution of the river-pebble proper of the west side of peninsular Florida, is approximately the same for the entire region. In this statement the rock-phosphates and bones of the northern streams are excluded. The impurity found in jthe product of the Caloosahatchee is extraneous, and con- sists very largely of carbonate of lime resulting from the intimate commingling with the pebbles of the remnants of the shells of Plio- cene and more recent formations, that have been washed into the bars from strata higher up the river.

Analyses Nos. 947 and 950 show the presence respectively of but 28.36 PA (61-91 CagPA) and 8-47 P2O5 (62.15 CeLjPjO) which may be regarded as the average for the class, but the percentage fre- quently rises to 29.32 per cent. PA (64.00 CslFJO, and occasion- ally even higher.

The contents in Al2(Fe2)03 are practically the same as in the better class of hard-rock phosphate ; the contents in CaO are some- what lower ; the insoluble matter is approximately the same as in the land-pebble, perhaps a little higher; and there is a perceptible increase in CO2 in the analyses given, and also considerable water at red heat.

The high percentage of insoluble matter in No. 947 is probably due to imperfect cleaning, although the sample was taken directly from the storage-bin after drying.

30 Pbeliminary Sketch Op The Phosphates Op Plorida.

The Black Creek phosphate differs from those of the west side of the peninsula in its diminished quantity of phosphoric anhydride and consequently of tricalcic phosphate. The sample taken (No. 1) containing 21.06 PjO (45.97 CajPjOg) affords about the average percentage.

Chemical Analyses of Florida Phosphates,

Loss (H,0) at

" red heat..

Cx),

Fl

Insol. resid. (in HCljHNOj) ( " HNO.)

Al,(Fe,)0,.

AlA

Fe,0,

CaO

MgO

Numbers of Samples.

2.29 2.27

toids 50.81

5.10 5.13

46;i2 4 614

PjOj X 2.183 CagPaOs. Habd Bock.

No. 25.— Typical gnj phosphate.

No. 42.— Mottled brown-and-white phosphate.

No. 55.— A rock containing cavities filled with loose sand, which readily shakes out.

No. 63.— Mammillary incrustation.

No. X4.— A fossiliferous phosphate, containing cavities with sand.

Pbeliminaby Sketch Of The Phosphates Of Florida. 31

Chemical Analyses of Florida Phosphates — continibed.

Lo68(Hj,0) at 105°... " red heat.

00,

Fl

Insol. reeid. (in HCl.HNOa) ( " HNO,)

Al,(Fe,)03

AlA

FeA

CaO

MgO

PKJ, .'MFfOS 37.83

Numbers of Samples.

74 A

74B

6.32 6.32

74 Bi

2.37 2.41

Wt.Oa

87.48 07 Aa

74 Ba

8.52 3.54

iJ;™ 84.69

74 Bs

7.80 7.79

W46 SJ-iJ iftlff' AH tA

29.96 AQ no

Habd Bock.

The general sample No. 74 was crashed and run through a lO-mesh sieve. 512 . Were

treated on a 20-me8h.

74 A portion coarser than 20-mesh, 184 ., or 85.88 per cent.

74 B — portion finer than 20*me8h, 328 ., or 64.62 per cent.

50 . of 74 B were washed in Thoulet tube with water, and gave of

74 Bi, the coarsest, dried at 106°, 17.05 ., — 34.10 per cent.

74 Bj, " middles, " " 7.50 " —15.00

74 B,, " finest, " " 28.06 " —46.10

Lost, suspended, 2.40 " — 4.80

32 Preliminary Sketch Op The Phosphates Of Florida,

Chemical Analyses of Florida Phosphates — contimied.

Loss (Hfi) at 105°..

" red heat.

Co,

Fl.

Insol.resid. (in HC1,HN02)

Hno,)

Alj(Fe,)Os.

AlA

Fe,0,

CaO

MgO

Pa

Numbers of Samples.

37.75 Q7

8.76 Q 7Q 8.80

82.68 Qo AQ

87 A

34.71 Oaqr

Habd Bock.

No. 74, Mix.— A mixture of the several products of the 74 series. No. 80.— White, coarsely-laminated phosphate, with clay In cavities. No. 83.— Gray variety of No. 80, typical. No. 87.— A close-textured, laminated rock, somewhat sandy. No. 87 A.— Portion of 87 coarser than 20-mesh.

Pbeliminary 8K£T0H Op The Phosphates Of Florida. S3

ChemiccUjAnalyaes of Florida Phosphates — contimied.

Loss (H2O) at 105°..

red heat.

Co,

Fl

Insol.resid. (in HC1,HN02) ( HNO2)

Al,(Fe2)0.

FeA.

CaO.. MgO.

Fa-

Numbers IH Samples.

87B

31.46 o-i J7

37.24 07 01

/.65

1:46 2.46

4.22 A 09

:07 50.08

38.82 Qq Qa

97A

23.98 nA ftQ

Habd Rock.

87 B.— Portion of 87 finer than 20-mesh. No. 89.— A type of close-textured laminated rock.

No. 96.— A mass of rock, yellow in the interior, white on the exterior, porous. No. 97.— Typical sandy phosphate ; indeed, a phosphatic sand-rock. General sample run through a 10-mesh sieve.. 97 A.— Portion of 97 coarser than 20-mesh ; 50 . 20.75 per cent.

34 Pbeuminaby Sketch Of The Ph08Phate8 Of Florida.

Chemical Analyses of Florida Phosphates — oonUnued.

Loss (H,0) at 106° " red heat.

Co,

Fl

Insol. resid. (in HCl,HNOs)

Hno,)

Numbers of Samples.

97B

Al2(Fe3)Os

A1,0,

Fe,Os

CaO

MgO

P2O5

7.70 7.70

97 Bi

2.96 2.95

13.74 107c:

97 Bt

7.99 7.97

97 B,

12: 10.50

l5.g 15.57

2.59 .2.58

7.93 7 85 7.78

44K)4

35.28 qe 10

Hard Bock.

97 B.Portion of 97 finer than 20-mesh ; 191 grams. — 79.27 per cent, washed with water in Tlioulet tube, and gave of 97 Bi, the coarsest, dried at 105°, 35.8 .l 47.73 per cent. 97 B,, middles, " " 19.75 " 26.33 97 Bs, the finest, " " 16.80 " — 22.40 Lost, suspended, 2.65 " 3.54

75 . of 97 B were

it

No. 98.— Typical, soft clay phosphate.

Preliminary Sketch Op The Phosphates Of Fix)Rida. 35

Chemical Analyses of Florida Phosphates—joontinued.

Loss (H,0) at 105°

00,

Fl

Numbers of Samples.

InsoLresid. (inHCl,HNO,)

Hno,)

p

Al,(Fe,)0,.

AlA

Fe,0,

CaO ...

MgO

SiOa

Pa

tS 2.02

2.31 2.32

%

100 A

39.66 OQ fiA

S:§J 47.02

Dttsolred. .10

33.91 oo 01

937A

2.73 9 79

47:94 47.95

Habd Bock.

No. 99.— Typical laminated phosphate, from same locality as 98. No. 100.— A granular-looking phosphate, light gray. 100 The coarser portion of 100, after separation on a 20-me8h sieve. No. 111.— A general sample of a property.

Lakd-Pebble.

987 A.— Washed pebbles.

36 Pb£Liminaby Bkbtoh Op The Ph08Phatjbb Of Flobida.

Chemical Analyses of Florida Phosphaies — concluded.

LoBB (H,0) at 105°

" red heat

Co, :

Fl '.

InsoLresid. (in HCl.HNOs) (" HNO3)

AUFe,)0,

Aia

Fe,0,

CaO

MgO

Pa

Numbers of Samples.

937 B

Izfl 13.58

46.06 Aft Ao

!l5? 31.50

28.33 QQ on

45.68 45 go

28.49 90 47

33.10 00 (\ft

2l:S6 21.06

Land Pebble.

937 B.~Matrix ftom which 967 A was washed. No. 940.— Washed pebbles from another locality.

River Pebble.

No. 947.— Peace River ; dried pebbles, from a bin.

No. 950.— Caloosahatchee River ; picked pebbles from a lighter-load.

No. 1.— Black Creek ; air-dried pebble.