IMPURITIES OF PHOSPHATE ROCK. 73 



are as a rule many intermediate stages, the load being taken up, 

 dropped again for a time, only to be once more started on its 

 journey. Among the primary results of concentration and enrich- 

 ment may be mentioned the phosphate deposits of the crystalline 

 rocks, where the mineral is found in veins, being more or less per- 

 fectly crystallized as the mineral apatite. Of deposits of this class 

 some, including those of Canada, are of economic importance, and 

 would be more extensively worked were it not that other and more 

 cheaply mined phosphate deposits are available. 



Of the phosphate taken into solution by the ground water a 

 part is taken up from the soils through the roots of plants, and thus 

 becomes a constituent of the plant life of the earth. From the 

 plants the phosphorus passes to herbivorous animals, and through 

 them to carnivorous animals. Phosphorus thus becomes a con- 

 stituent of the organic life of the earth. The bones of the verte- 

 brate animals in particular contain an appreciable amount of cal- 

 cium phosphate. It seems well established also that certain of the 

 important phosphate deposits,' as well as the guano deposits are 

 derived from excrement and remairfs of gregarious animals, par- 

 ticularly birds. It is also true that a part of the phosphate taken 

 into solution by the ground waters is again thrown out owing to 

 changed chemical conditions, and in this way important phosphate 

 deposits are formed. In any case, however, the phosphate may 

 be regarded as only temporarily delayed in its round of circula- 

 tion. . Ultimately phosphate is carried in solution in the ground 

 waters through springs and rivers to the ocean. While the amount 

 in solution at any one time is relatively small, yet, through the con- 

 tinued operation of this agency over long periods of time, a large 

 amount has been carried into the ocean. 



The phosphate carried into the ocean is again removed from 

 solution through the agency of organic life, or owing to changed 

 chemical conditions, is precipitated. Of the animals that utilize 

 phosphorus taken from the sea water in the construction of a 

 shell covering or skeleton, the best known perhaps is the brachi- 

 opod, Lingula, the shell of a recent species of- which has been 

 found to contain 85.79 P^^' cent of calcium phosphate. The test? 

 of the Crustacea, although less distincMy phosphatic than the sheP 

 of Lingula, contain an appreciable amount of phosphate. Thus 

 the shell of a recent lobster was found to contain 3.26 per cent of 



