intimately mixed up with the bones and teeth of numerous extinct species.

The only difference between them and the "land" pebbles, is that the latter are of a lighter color and are imbedded in a matrix of sand and clay, to which they frequently bear the proportion of about twenty per cent. by weight.

Although the origin of these Florida deposits has naturally been very much discussed, and a great number of more or less plausible theories has been advanced, I doubt whether any particular one has yet been sufficiently supported by evidence to warrant its general acceptance. I have personally devoted to it a great deal of observation and thought, and so far as I have gone I believe the most satisfactory explanation is that which ascribes them to a deposition resulting from previous solution. Apart from the probable existence of bird guano deposits in large quantities on their exposed surfaces, the Vicksburgh limestones all contain in themselves notable proportions of phosphate of lime, and the seas of that age were certainly charged with sufficient carbon dioxide to dissolve both carbonate and phosphate of lime in large quantities. Having entered into solution the phosphate, at a subsequent period, was re-deposited under conditions favorable to its separation. What these conditions most probably were I need not pause to discuss at any length, but I think it will be obvious that they might have been either a simple interchange of bases between the dissolved phosphate and the limestone bed, or a mere lowering of the solvent powers of the water by evaporation and loss of carbonic acid gas. In either case the final result would be the formation, principally in the neighborhood of the rock cavities produced by the leaching process, of large and small estuaries, and those estuaries being certainly replete up to a certain point, with life and vegetable matter, the continuous concentration of the waters ultimately induced complete precipitation and a multitude of readily conceivable subsequent processes of decomposition and metamorphism.

It may be very rationally surmised, for example, that among the chief of these processes and decompositions, when the "drying-up" was nearly complete, would be the

combination of the liberated phosphoric acid, and the ammonia, resulting from the breaking up of the albuminoids of the organic matter. The diammonium phosphate thus formed would be dissolved by subsequent waters, and, percolating through the overlying mass of the deposit, would saturate the calcareous marls as well as the soft and porous limestone underneath. A double decomposition would thus be induced, with formation of hydrogen calcium phosphate and ammonium carbonate: 2 (NH4)2 H(PO4) + 2 CaCO3 Ca2 H2 P2O8 + 2 (NH4)2 CO 3.

2

2

In whatever manner it was originally formed, whether as a residium from leaching, a deposition from solution, or a product of decomposition and metamorphism, the phosphatized stratum was eventually cracked and broken up and was then hurled into yawning gaps and from one fissure to another. At the end of the tertiary period came the suc. ceeding seas with their deposits of drifts and shells, sands, marls, clays and other transported material, and it is easy to assume that those portions of the phosphate crust which were not embedded in permanent limestone fissures or caverns during the Miocene age, subsequently became very thoroughly disseminated and disintegrated. The masses were rolled about and intermixed with sand, clay, and marls, and were banked up with them in various mounds or buried in depressions in conformity with the violence of the waters, or with the uneven structure of the surface to which they were transported.

Occasionally this drifting mass found its way into very deep hollows, in regions where considerable depressions were brought about by the sinking and settling of the substratum. At other times it was rolled to and deposited on slightly higher points. In the first of these cases we find a vast and complete agglomeration, comparable to an immense pocket, of broken-up phosphate rock, finely divided phosphate débris, sands, clays and marls, all heterogenously mixed in together. In the second case we find the phosphate in large bowlders, sometimes weighing several tons and intermixed with relatively, but, small proportions of any foreign substance.

THE CHEMICAL COMPOSITION OF FLORIDA PHOSPHATE

is as variable as its physical aspects, and I present the fol lowing averages of my own analyses for the purpose of gen

It will be seen from these figures that, quite apart from its abundance, we are dealing with a product of the very first rank for the purposes of the fertilizer manufacturer. The unfortunate fact remains, however, that owing to certain established trade customs arising out of the long-continued use of South Carolina phosphate, there is no remunerative market in our own country at the present time for high-grade material, and this, consequently, has to be exported. Similarly established trade customs. arising out of similar causes, prohibit foreign buyers from accepting any phosphates containing a higher maximum than three per cent. of oxides of iron and alumina, and this compels our miners to guarantee an absolute limit to these impurities in all their shipments.

The now generally adopted plan for working the bowlder deposits in such a way as to free them as far as possible from the undesirable iron and alumina, chiefly present as adhering particles of clay, was, I believe, first suggested by myself in 1890. It consists in crushing all the big boulder rock to a sufficiently small size, and passing it, together with all the débris that comes from the mine, through washers of the type known as the Tennessee log-washer. After being

thus entirely freed from sand and clay, and passed through screens of various sizes, it is finally dried in open kilns, built up on logs of pine. The cost of production in this method of mining when economically carried out, as it is, for instance, in the washing-plants built by McLanahan & Stone, averages about $3.50 per ton and there is no waste of phosphate.

The land pebble phosphates have not yet been extensively worked, and as they are even more intimately mixed up with clays than the hard rock phosphate, there is still some doubt as to the most economical way of winning them. Some of the large concerns in Polk County employ a floating dipper-dredge set in a deep trench, which is deepened and extended as the deposit is removed. The entire mass of phosphate and matrix is brought up to the surface by the dredge, and, as in the case of the bowlder rock mines, is first dropped into a species of disintegrator or crusher. Thence it passes on into a revolving-washer mounted on the same structure. From the washer, the matrix and water return to the trench, while the clean nodules are carried by a spiral conveyor to a steam-heated dryer on a barge alongside. From the dryer they fall into a revolving-screen, which removes any remaining particles of adhering sand, and the now marketable phosphate is caught up by elevators and delivered on board railway-cars standing on a track parallel with the trench.

The exploitation of the "river pebble" is performed by means of a ten-inch centrifugal steam suction-pump placed upon a barge. The pipe of the pump having been adjusted by ropes and pulleys, is plunged ahead from the deck of the dredge into the water. The mixture of sand and phosphate sucked up by it is brought into revolving-screens of various degrees of fineness, whence the sand is washed back into the river. The cleaned pebbles can be discharged from the screen into scows at the rate of about twelve tons per hour, and the product is floated down to the drying-house, where it is taken up by an elevator and dried by hot air.

The total cost of raising, washing, drying, screening and loading "pebble" phosphates on cars, is stated to be $2 per

ton.

As in the case of South Carolina, I have compiled the following table, showing the quantity of

PHOSPHATE (ROCK AND PEBble) of all GRADES MINED BY THE LAND AND

RIVER COMPANIES OF FLORIDA SINCE THE DISCOVERY OF

I have now finished what is, at the best, only a very brief and rough description of our phosphate beds, and I should probably best recognize your endurance by at once releasing you. While I freely recognize, however, that I shall be imposing on your good nature if I crave your indulgence for a few moments longer, I venture to do so because I much wish to touch upon two very important points bearing on my subject. The first of these relates to the practical use of phosphate of lime by the agriculturist, and the second to the desirability of universally adopting some correct and definite method for its analysis.

The phosphate miner, as we have seen, does not sell his product to the farmer, but to the manufacturers of fertil izers, who first grind it to an extreme fineness, and then mix the powder with about its own weight of weak sulphuric acid. Two out of the three molecules of lime originally combined with the phosphoric acid, being thus transformed into gypsum, a more or less soluble article is obtained which is the basis of all artificial fertilizers, and which is popu. larly known as superphosphate. The reason why this acidulated compound is preferred to the raw material is to be found in the generally admitted fact that tricalcium phosphate is very sparingly and very slowly soluble in the water of the soil, and that no element can penetrate into the interior of a plant unless it be in solution.

A great many attempts to use it as a direct fertilizer have demonstrated that the availability of raw mineral phosphate entirely depends upon the fineness of the powder to which it may be reduced, and the nature and composi