598 Mansfield — Western Phosphates of United States. 



of marine currents, checked the activities of the denitri- 

 fying bacteria and hence the conditions favorable for the 

 formation of oolitic limestone. At the same time plant 

 and animal life increased in the waters and furnished the 

 decaying matter necessary for the phosphatization of the 

 oolitic limestone in the general manner set forth in Black- 

 welder's account given above. Perhaps Pardee's idea of 

 glacial climate may have a bearing in this connection. 



6. The temperature change may have been sufficiently 

 abrupt to cause the wholesale killing of certain marine 

 animals, as suggested in Blackwelder's account. This 

 would supply material for a fairly rapid phosphatization 

 of the oolitic limestone. Such an assumption, however, 

 is not compulsory because the phosphatic shales as a 

 whole were doubtless formed slowly and there was time 

 for sufficient accumulation and trituration of organic 

 remains to produce the observed phosphatization before 

 the moderate crustal changes that permitted the introduc- 

 tion of the clastic material that buried the phosphate bed. 



7. The conditions set forth above, which were out- 

 lined particularly with reference to the main phosphate 

 bed, probably were repeated on a less extensive scale for 

 the lesser beds. Shaly partings or minor shale beds in 

 the phosphate might be explained as the result of occa- 

 sional seaward drift of land-derived silts after some 

 unusual or protracted storm. 



8. The sea in which the phosphate was deposited was 

 closed off on the east, south and west, but may have had 

 connections with the ocean northward and northwest- 

 ward, for Girty 22 notes f aunal resemblances traceable into 

 Alaska, Asia, and eastern Europe, and Adams and Dick 23 

 report the discovery of phosphate at apparently the same 

 horizon in Alberta. 



22 Girty, G. EL, op. cit., p. 9. 



23 Adams, F. D., and Dick, W. J., Discovery of phosphate of lime in the 

 Eocky Mountains, Commission of Conservation, Canada, Ottawa, 1915. 



