CHAPTER yil. 



STEATIGEAPHY — CENOZOIC FORMATIONS. 



In the present chapter I shall take up the remaining members of the 

 sedimentary series as exposed in our district. These consist mainly of 

 beds referable to the Green Eiver and Bridger groups of the Tertiary, 

 and I shall consider them without entering into any extended discussion 

 as to the exact names that should be given them, whether Eocene or 

 Miocene. Professors Cope, Leidy, and Marsh consider them Eocene, 

 basing this conclusion on the discovery of vertebrate organic remains ; 

 while Lesquereux relers there to the Miocene from his investigations of 

 their fossil flora, calling the "Lignitic" group Eocene. I shall simply 

 describe the beds, giving the local names of the groups to which they 

 are referred. 



In regard to the "Lignitic" group, I am unable to present any details. 

 Farher discussion as to the exact age of the group will be found in the 

 other reports. 



As to the Post-Tertiary formations, I am able to speak only in the 

 most general way, and am unable to separate them into groups. 



TERTIAE.Y. 



A bove the beds characterized as Cretaceous by their lithological pe- 

 culiarities and the occurrence of typical fossils, is a series of beds from 

 7,000 to 8,000 feet in thickness, covering a large area extending from 

 the Grand Eiver to the Gunnison beneath the basaltic plateaus west of 

 Eoaring Fork. This area is marked on map E. 



The best exposures are seen on Plateau Creek. I had time only to 

 make a partial detailed section. The strata are conformable to the un- 

 derlying Cretaceous, and it is difiQcult to determine where one forma- 

 tion ends and the next begins. I have arbitrarily chosen as the base of the 

 Bridger series a bed of red sandstone that is tolerably persistent beneath 

 the variegated beds above which the fossils were found. Another year 

 I hope to define the limits of the formation. The lower portion of the 

 series is referred to the Tertiary with soine hesitation, as the fossils, » 

 which were few in number, were found too far above to predicate any- 

 thing very definitely. Before entering into any description of the groups 

 as they occur in our district, I will give in tabular form the various 

 views held by different authorities in regard to the beds that have been 

 referred to the Te]|fiary formations with the exception of those referred 

 to the Pliocene. 



140 



