Phosphates Their Sources 69 



in several different forms, and are procured from distinct 

 sources. 



South Carolina rock phosphates. 



These are found both on the land and in the beds of 

 rivers in the vicinity of Charleston, South Carolina, and 

 are sometimes called "Charleston phosphates." The de- 

 posits vary in thickness from one to twenty feet, through 

 which the phosphate is distributed in the form of lumps 

 or nodules, ranging in weight from an ounce to over a ton. 

 These nodules are irregular, non-crystalline masses, often 

 full of holes, which contain clay or other non-phosphatic 

 materials. That obtained from the river is called "river 

 phosphate," or "river rock"; and that from the land, 

 "land phosphate," or "land rock." The two varieties 

 do not differ materially in composition, particularly in 

 the content of phosphoric acid. 



The rock contains from 26 to 28 per cent of phosphoric 

 acid. Its uniformity, in connection with the fact that it 

 contains but small percentages of compounds of iron and 

 alumina, minerals which prevent its best use by the 

 manufacturer, make it a highly satisfactory source of 

 phosphoric acid. 



The river rock is secured by dredging; that from the 

 land is largely dug. In either case it is washed to re- 

 move the adhering matter, and then dried, when it is 

 ready for grinding or shipment. South Carolina rock 

 phosphate, when very finely ground, is called "floats." 

 It is sometimes used upon the land in this form, and 

 when used for certain crops, as turnips, for example, and 

 on certain soils, notably those wet and heavy and rich in 

 vegetable matter, very satisfactory returns are obtained. 



These deposits were first worked in 1868, though the 



