Mansfield — W estern Phosphates of United States. 593 



tive account of the cycle of changes undergone by phos- 

 phorus from apatites through solution, assimilation by 

 plants or animals, deposition on sea bottom or on land, 

 accumulation into deposits, burial, deformation, and 

 metamorphism back to apatites again. Many subcycles 

 are included and individual atoms of phosphorus may 

 have had widely different histories. In the second 8 he 

 gives in abbreviated form, as derived from available 

 literature, a view of organic accumulation, which is sub- 

 stantially repeated here for reference. In the ocean 

 special conditions of currents, temperature, etc., not yet- 

 understood, may have induced wholesale killing of 

 animals over large areas and accumulation of putrefying 

 matter on the sea floor in moderate and shallow depths. 

 Decomposition through the agency of bacteria produced 

 ammoniacal solutions which dissolved the solid calcium 

 phosphate in bones, teeth, brachiopod shells, and tissues. 

 Putrefactive conditions also prevented the existence of 

 organisms attached to the bottom and most calcareous 

 shells descending from the surface were probably dissolved 

 by the abundant carbonic acid arising from decay. For 

 physico-chemical reasons, already partly understood, the 

 phosphatic material was quickly redeposited in the form 

 of hydrous calcium carbo-phosphates, locally filling, 

 incrusting, and replacing shells, teeth, bones, etc., but 

 especially forming small rounded granules of colophanite 

 and finally a phosphatic cement among all particles. The 

 granular texture is ascribed chiefly to physico-chemical 

 conditions, such as result in oolitic greenalite, limonite, 

 aragonite, etc. After having been formed in quiet water 

 some of the granules were reached by bottom-scouring 

 currents and incorporated in clastic deposits and in some 

 instances were strewn over eroded rock surfaces and so 

 became constituents of basal conglomerates. 



The latest contributor to the origin of the Western 

 phosphates is Pardee, 9 who is inclined to look with dis- 

 favor upon the view that unusual or abundant sources 

 supplied phosphates rapidly to the sea. He points to 

 the existence of glacial conditions elsewhere in Permian 

 times, and suggests that cool temperatures may have pre- 

 vailed during the deposition of the Western phosphates. 



s Blackwelder, Eliot, Origin of the Bocky Mountain phosphate deposits, 

 Bull. Geol. Soc. America, vol. 26, pp. 100-101, 1915. (Abstract.) 



9 Pardee, J. T., The Garrison and Philipsburg phosphate fields, Montana, 

 U. S. Geol. Survey, Bull. 640, pp. 225-228, 1917. 



