248 desceiptivp: geology. 



An analysis of this cement, made by Mr. B. E. Brewster, gave : 



Silica.- : 11.902 



Soluble silica 0.405 



Alumina and Ferric oxide 0.781 



Lime". 47.007 



Magnesia 0.489 



Carbonic acid ' J / 37.079 



Water and organic matter 2.409 



100.072 



The insoluble silica doubtless comes from a mechanical mixture of fine 

 sand. As the beds of the Wyoming Conglomerate, as far as observed, are 

 entirely devoid of all organic remains, the only evidence of their geological 

 age is obtained from their relative stratigraphical position, from which it is 

 deduced that they were deposited probably not long anterior to the Glacial 

 period. 



The molluscan remains of the Bridger beds, which are found principally 

 in the lower part of the formation, hardly distinguish them in age from the 

 other groups in this basin. Those which have been described belong to 

 the following fresh-water species : 



Unio Haydeni. 



Planorbis spedabilis. 



Planorhis spectahilis var. Utahensis. 



Limncea (LimnopJiysa) vetustus. 



Limnma similis. 



Goniohasis Simpsoni. 



Goniohasis arcta. 



Goniohasis tenera. 



Viviparus paludinm formis. 



Viviparus Wyomingensis. 



Pupa Leidyi. 



The vertebrate remains, of which large collections have been made by 

 Professor Marsh and his assistants, will be found specifically described by 

 him in a later volume. They indicate a Middle or Lower Eocene horizon, 



