26 AGRICULTURAL ANALYSIS 



The third group of phosphates in order of age and assimila- 

 bility embraces the true phosphorites containing generally some 

 organic matter. They are all of organic origin. 



In caves where animal remains are deposited there is an ac- 

 cumulation of nitrates and phosphates. Not only do the bones 

 of animals furnish phosphates but they are also formed in consid- 

 erable quantities by the decomposition of substituted glycerids 

 such as lecithin. The ammonia produced by the nitrification of 

 the albuminoid bodies combines with the free phosphoric acid 

 thus produced, forming ammonium or diammonium phosphates. 

 The presence of ammonium phosphates in guanos was first noticed 

 by Chevreul. 



If such deposits overlay a pervious stratum of calcium car- 

 bonate, such as chalk, and are subject to leaching, a double de- 

 composition takes place as the lye percolates through the chalk. 

 Acid calcium phosphate and ammonium carbonate are produced. 

 By further nitrification and solution the latter becomes finally 

 converted into calcium nitrate. In like manner aluminum phos- 

 phates are formed by the action of decomposing organic matter 

 on clay. 



Davidson explains the origin of the Florida phosphates by sug- 

 gesting that they arose chiefly through the influx of animals 

 driven southward during the glacial period. 14 According to his 

 supposition, the waters of the ocean, during the cenozoic period, 

 contained more phosphorus than at the present time. The 

 waters of the ocean over Florida were shallow and the shell fish 

 existing therein may have secreted phosphate as well as car- 

 bonate of lime. This supposition is supported by an analysis of 

 a shell of lingula ovalis, quoted by Dana, in which there was 

 85.79 P er cent - f nme phosphate. In these waters were also 

 many fishes of all kinds and their debris served to increase the 

 amount of phosphatic material. As the land emerged from the sea 

 came the great glacial epoch, driving all terrestrial animals south- 

 ward. There was, therefore, a great mammal horde in the 

 swamps and estuaries of Florida. The bones of these animals 

 contributed largely to the phosphatic deposits. In addition to 

 14 Wyatt, Phosphates of America, 4th Edition, 1892 : 66. 



