592 Mansfield — Western Phosphates of United States. 



ary origin, they might be expected to pass at compara- 

 tively shallow depths into unleashed low grade phosphate 

 or even into phosphatic limestones. Tims the valuable 

 deposits would be limited to a comparatively short dis- 

 tance from the outcrop and the great body of rock under 

 cover in the synclines would be valueless. ' Probably 

 absolute certainty on this point cannot be reached without 

 deep drilling. On the other hand the phosphate beds 

 have been observed in many parts of the region and under 

 many conditions by a number of geologists and every- 

 where they appear to be true bedded deposits analogous 

 to coal or limestone, retaining their thickness and quality 

 over wide areas. For these reasons they are regarded 

 as original sedimentary deposits and it is considered 

 probable that they maintain at depth the characteristics 

 displayed at the surface. Upon this assumption rest the 

 estimates given for the Western field. 



The sources of the phosphoric acid and the methods 

 of accumulation are to a considerable degree subjects of 

 speculation, but it will perhaps be helpful to summarize 

 opinions thus far advanced and to indicate the probable 

 direction of solution of the problems involved. 



The first detailed accounts of the Western phosphates 

 are contained in papers of Gale and Richards 3 and Black- 

 welder. 4 These authors regard the phosphates as orig- 

 inal marine sedimentary deposits and the first two give 

 a very brief summary of the hitherto recognized sources 

 of phosphorus and the means of its accumulation as 

 phosphates 5 through the agency of organic and physico- 

 chemical processes, Because of the relative scarcity of 

 organic remains in the actual phosphate beds, Richards 

 and Mansfield 6 were inclined to place greater emphasis 

 on physico-chemical than on organic sources and agencies. 



Blackwelder has contributed two important later 

 papers. In the first 7 he gives an interesting and sugges- 



3 Gale, H. S., and Richards, R. W., Preliminary report on the phosphate 

 deposits in southeastern Idaho and adjacent parts of Wyoming and Utah, 

 U. S. Geol. Survey, Bull. 430, pp. 457-535, 1910. 



* Blackwelder, Eliot, Phosphate deposits east of Ogden, Utah, U. S. Geol. 

 Survey, Bull. 430, pp. 536-551, 1910. 



5 Gale, H. S., and Richards, R. W., op. cit., pp. 461-462. 



6 Richards, R. W., and Mansfield, G. R., Preliminary report on a portion 

 of the Idaho phosphate reserve, U. S. Geol. Survey, Bull. 470, pp. 376-377, 

 1911. 



Geology of the phosphate deposits northeast of 



Georgetown, Idaho, U. S. Geol. Survey, Bull. 577, p. 74, 1914. 



7 Blackwelder, Eliot, The geologic role of phosphorus, this Journal, vol. 

 42, pp. 285-298, 1916. 



