2!»4 Blachwelder — The Geologic Role of Phos2)horus. 



teracting with the iron compounds, forma the mineral pyrite, 

 which is common in certain types of black shales. In a similar 

 way, phosphoric acid in the presence of ammonia reacts with 

 various substances, and especially lime carbonates, in such a 

 way as to produce phosphatic minerals, of which the com- 

 monest is collophanite, — said to be hydrous calcium carbo- 

 phosphate. These changes have been carried out experimen- 

 tally in the laboratory by several investigators, and the neces- 

 sary conditions are such as may readily occur on the sea bottom 

 where organic decomposition is in progress. The calcareous 

 shells and fragments lying on the ocean floor thus become 

 phosphatized, and even such organic materials as excretory 

 pellets and pieces of wood are known to have been altered in 

 the same way. Bones, which initially contained about 58 per 

 cent tricalcium phosphate, have their organic matter completely 

 replaced by phosphatic minerals, thus raising the ratio to 85 

 per cent or more. In addition, collophanite is precipitated in 

 concentric layers around particles of sand or any solids, form- 

 ing round or elliptical granules which resemble the oolitic 

 grains in certain limestones. By the enlargement of these 

 coatings, the granules, shells, teeth and other objects are 

 cemented into hard nodules or even into continuous beds of 

 phosphatic rock. Such nodules have been dredged up from 

 the bottom of all the oceans in moderate depths, and are not 

 uncommon in certain kinds of marine limestones aud shales 

 now on land. 



The marine phosphatic sediments now constitute our greatest 

 bodies of commercial rock phosphates, exemplified in the 

 phosphate beds of Tunis, Algeria, England, and — most extensive 

 of them all, — those of the Rocky Mountains of Idaho, Utah 

 and Wyoming. In many other places, such as the Carolinas, 

 Florida, Belgium, and northern France, marine sediments 

 containing only 1 to 5 per cent P 2 5 have, through secondary 

 concentration in later ages, produced rich phosphatic deposits. 



Reference has already been made to the fact that, through 

 the agency of land-animals such as birds, the phosphorus may 

 escape from the charmed circle of its metamorphoses in the 

 ocean. Upon islands where they are out of reach of predaceous 

 animals, seabirds congregate in extraordinary numbers, and the 

 amount of excrement annually deposited by them upon the 

 surface of these islands is large. Ridgeway* cites evidence 

 that it accumulates locally at the rate of about 1£ inches per 

 year. The material is comparatively rich in phosphorus, owing 

 in part to the fact that the birds feed largely upon the bony 

 fishes ; but it seems to exist chiefly in the form of insoluble 

 organic phosphates which are not affected by unaided rain 



* Quoted by G. P. Merrill, Non-metallic Minerals, p. 267. 



