72 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT, 



that while the phosphate dissolves freely in waters containing decay- 

 ing organic matter and in carbonated waters, yet when allowed 

 to stand over calcium carbonate, the phosphate is redeposited. In 

 summing up his observations Reese says : "This experiment shows 

 that phosphates may be transported in hard waters, but on stand- 

 ing on calcareous beds would tend to be given up." In speaking 

 of hard waters the author evidently has in mind waters contain- 

 ing, among other things, carbon dioxide in solution, and his con- 

 clusion is that such waters will or may drop the calcium phosphate 

 from solution when they stand over limestone. These observa- 

 tions, if true, have two important corollaries, one of which has been 

 noted by Clarke, (U. S. Geol. Surv. Bull. 330, p. 443, 1908) namely, 

 that in the presence of the carbonate, the phosphate would prob- 

 ably not be dissolved, while the carbonate could pass into solution, 

 thus leaving the enriched residue of phosphate. The second corol- 

 lary is that calcium phosphate taken into solution by the soil waters 

 at and near the surface may be thrown out of solution in case the 

 water stands for a time at a lower level in the earth on or over 

 limestones. That this process may have been and probably was a 

 factor in the formation of large phosphate deposits resting upon 

 limestone will be shown in the subsequent pages of this paper. 



The rain water, in passing through the soil and surface mate- 

 rials, receives organic acids from the decay of vegetable and ani- 

 mal matter. It also receives carbonic acid which is held in solu- 

 tion, the water thus becoming carbonated, and hence more efficient 

 as a solvent. The original rocks and the soils derived from them 

 contain particles of the phosphate minerals, which when acted 

 upon by the ground waters pass slowly into solution. It is through 

 the solution of the mineral, its removal and subsequent redeposi- 

 tion that workable phosphate deposits are formed. When it is 

 remembered that the phosphorus in the igneous rocks amounts to 

 merely a fractional part of one per cent of the whole,* and was 

 without doubt originally widely disseminated, the importance of 

 the processes of concentration of the mineral by ground water and 

 the extent to which they have operated becomes evident. 



The removal of the mineral from the original rocks and its con- 

 centration in later rocks is by no means a simple process. There 



♦According to Clarke, Bulletin 330, U. S. Geological Survey, p. 32, 1908, 

 the phosphorus in the lithosphere amounts to only .11 per cent. 



