PHOSPHATE DEPOSITS OF THE SOUTHERN STATES. QI 



The land pebble phosphate deposits of southern Florida are 

 much more uniform in their manner of occurrence than are the 

 hard rock deposits. The phosphate is in the form of pebble rock 

 imbedded in a matrix of clay, sand and soft phosphate. Although 

 variable from place to place the phosphate bed has an average 

 thickness of from 8 to lo feet, its maximum thickness being from 

 1 8 to 20 feet. The overburden, which consists largely of sand 

 and sandy clays, with local indurated or calcareous ledges, has an 

 average thickness of from lo to 14 feet. 



The best grade of land pebble rock when properly washed, dried 

 and selected permits a guarantee of 75 or 76 per cent tricalcium 

 phosphate. Other grades on the market range from 62 to 75 per 

 cent. The hard rock phosphates average from 79 to 83 per cent, 

 although selected samples run as high as 84 or 85 per cent trical- 

 cium phosphate. 



Practically all of the hard rock phosphate mined in Florida is 

 exported, that used in America amounting to not more than 15 or 

 18 thousand tons per annum. Of the land pebble phosphate pro- 

 duced a little more than one-third is now being exported. 



KENTUCKY. 



The phosphate deposits in Kentucky resemble in a general way 

 the brown rock of Tennessee. According to Gardner* the phos- 

 phate is in the form of loose rock, consisting of thin plates and 

 finely comminuted material mixed with some clay, the whole being 

 of a dark brown color. The hard rock plates vary from light gray 

 to dark brown and are usually rather dense. These plates vary in 

 size from the granular form up to pieces that weigh several pounds. 

 The deposits as a whole occur in blanket form on limestone and 

 are covered by clay and soil. As in the case of the brown rock 

 phosphate of Tennessee the deposits are extremely irregular both 

 as to thickness and extent. Gardner states that the deposits orig- 

 inate from secondary concentration from the process of weathering 

 of phosphatic limestone. The surface of the underlying rock is 

 irregular and naturally the bottom of the phosphate conforms with 

 it; at some places it suddenly deepens and at others rock horses 

 rise in the phosphate beds. The cover of clay and soil varies from 

 about 2 to more than 10 feet, being thicker on the tops than on 

 the sides of hills and ridges. 



*Rock Phosphate in Kentucky: Mines and Minerals, Nov., 1912, pp. 207-209. 



