PHOSPHATE ROCK 441 



Tho various doposits of phospliatir niatfrial liavo not yot 

 been classified geologically owing to the ililliculty in dctennin- 

 ing the position of several of the deposits, augmented hy the 

 large number of forms which the phosphate assumes and the 

 complex blending of certain varieties. The common technical 

 classification makes the l)road distinction between mineral 

 phosphates, whose origin can not be traced to animal life, and 

 rock phosphates, more or less mineralized, but directly trace- 

 able to an organic origin. On this Ijasis the only mineral phos- 

 phates are those containing crystalline apatite, which occur in 

 Canada, Norw^ay, and a few localities in Spain. The deposits 

 at Nassau, Germany, Lot-et-Garonne, Tarn-et-Garonne, and 

 Aveyron in France, and Logrosan and Caceres in Spain are us- 

 ually included in the mineral phosphates under the arbitrar>' 

 and indefinite term phosphates. The term rock phosphates 

 includes the remaining varieties of phosphatic limestone, coi>- 

 roHtes, nodular phosphates, concretionary phosphates, arena- 

 ceous phosphates, sheet rock phosphates, and Ijone beds. 



The value of phosphate rock in the United States lies sole- 

 ly in its use as a fertilizer to enrich land impovtn'ished by con- 

 tinual removal of crops that have grown thereon, or land which 

 did not originally possess the components necessary for the 

 normal growth and development of plant life. 



It has been only within comparatively recent years that 

 the relation between plants and soils has been scientifically 

 studied. In general the manner of life in plants resembles 

 that of animals or man, in that they require certain footls in 

 stated proportions which are digested or assimilated, they 

 must breathe a certain atmosphere, and they are subject to 

 the influence of heat and cold, light and darkness. The t issues 

 of plants, like those of animals, are composed of carbon, hydro- 

 gen, oxygen, nitrogen, and certain mineral acids or bases, not- 

 ably phosphoric and sulphuric acids, lime, magnesia, iron and 

 potash; and the growth of a plant bears a close relation to that 

 of an animal for the reason that it constantly absorbs elements 

 from the soil and air to build up its structure. The relation 

 of plant Hfe to animal hfe is reciprocal. Animals breathe 111 

 the oxygen of the air and convert a small part of it into carbon 

 dioxide, which is exhaled and returned to the air, while plants, 



