228 THE WASTE AND CONSERVATION OF PLANT FOOD. 



order in age Gautier places the pbosphates of hydro-mineral origin. 

 This class not only embraces the crystalline apatites, but also those 

 phosphates of later formation formed from hot mineral waters in the 

 Jurassic, Cretaceous, and Tertiary deposits. 



These deposits are not directly suited to nourish plants. 



The third group of phosphates in order of age and assimilability 

 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 accumulation of nitrates and phosi)hates. 



Not only do the bones of animals furnish phosphates, but they are 

 also formed in considerable quantities by the decomj)Osition of substi- 

 tuted glycerides, such as lecithin. 



The ammonia produced by the nitrification of the albuminoid bodies 

 combines with the free phosphoric acid thus produced, forming aumio- 

 nium or dianimouium phosphates. 



The presence of ammonium phosphates in guanos was first noticed 

 by (Jhevreul more than half a century ago. 



If such deposits overlay a i)ervious stratum of calcium carbonate, 

 such as chalk, and are subject to leaching, a double decomposition 

 takes place as the lye percolates through the chalk. Acid calcium 

 l)hosphate, and ammonium carbonate are produced. By further nitrifi- 

 cation the latter becomes finally converted into calcium nitrate. In 

 like manner aluminum i)hos[)hates are formed by the action of decom- 

 posing 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 by the Glacial i^eriod. According to his sux)position the 

 waters of the ocean, during the Cenozoic period contained more phos- 

 phorus than at the present time. The waters of the ocean over Florida 

 were shallow, and the shellfish existing therein may have secreted 

 phosphate as well as carbonate of lime. This supposition is sujjported 

 by an analysis of a shell of TAngula oralis, quotcMl by Dana, in which 

 there was .85.70 per cent of lime phosphate. In these waters were 

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

 amount of this substance. As the land emerged from the sea, came 

 the great Glacial epoch driving all terrestrial animals southward. 

 There was therefore a great mammal horde in the swamps and estua- 

 ries of Florida. The bones of these animals contributed largely to the 

 phosphatic deposits. In addition to this, the shallow sea contained 

 innumerable sharks, manatees, whales, and other inhabitants of trop- 

 ical waters, and the remains of these animals added to the phosphatic 

 store. 



While these changes were taking place in the Quaternary period, 

 the Florida peninsula was gradually rising, and, as soon as it reached 



'Engineering and Mining Journal, quoted in the Phosphates of America, by 

 Wyatt, page 66 et sei^. 



