LOXOLOPHODON AND UINTATHERIUM. 



II 



ary rock ; these had not shared in the general submergence which preceded 

 the deposition of the Laramie. On the flanks of the Wahsatch hills were 

 Mesozoic and Carboniferous beds, and the same strata were exposed on the 

 Uinta slopes. 



The degradation of these older strata, if we can judge from the investigations 

 of Major Powell ' in the Uinta range, taking place pari passu with upheaval, 

 was on a grand scale. Vast quantities of water were borne by the winds from 

 the Pacific Ocean, as yet uninterrupted by the Sierra range, and were condensed 

 on the Uinta slopes. The sediments thus collected formed the Vermillion 

 Creek group of rocks — so named from their prevailing red color. They lie 

 unconformably over the Laramie strata, and are highly fossiliferous. The most 

 characteristic mammal at this period was Coryphodon, five-toed and with a full 

 dentition. The presence of this with Hyracotherium, Hyopsodus, Opisthotomus, 

 Amblyctonus, Clastes, and others, has led Prof. Cope' to indicate the close paral- 

 lelism between these beds and the Suessonian or Orthrocene of Europe, in 

 which these genera also abounded. 



The middlemost member of the Eocene series, the Green River group, 

 was deposited over a still larger area ; for after the Vermillion Creek beds 

 were formed, the western, and in some degree the eastern, borders of the Ute 

 Lake subsided, enlarging the basin to nearly double its former size. This 

 second lake, named the Gosiute Lake, in which the Green River beds were 

 slowly deposited, was an almost uninterrupted sheet of water, extending about 

 three hundred miles on the fortieth parallel, and one hundred and fifty north 

 and south. 



While the close of the Vermillion Creek deposition was marked by an 

 expansion of the basin borders, the close of the Green River deposition was 

 marked by contraction ; so that the third member of the Eocene series, the 

 Bridger beds, was deposited in a smaller basin. According to Powell, a dry- 

 land period also intervened. It followed that when the limits of the third 

 lake were defined, they were on all but the southern side within the area of the 

 Vermillion Creek beds. The oscillations of level which preceded it and the 

 contour of the present exposures of the beds, formed in this third or Washakie 

 Lake, leave considerable doubt whether it was a continuous sheet of water 

 enclosed in a single basin or several smaller basins, with a common southerly 

 outlet. This question will be resumed further on. 



A liberal estimate of the total thickness of these three groups of Eocene rocks 

 is 9500 feet. Powell estimates them at 6000 feet. They form the lower, mid- 



• Geology of the Uinta Mountains. Washington, 1876. 



' Ext. Bull. U. S. Geol. and Geog. Survey, Feb. 28th, 1879. The Relations of Horizons of Extinct 

 Vertebrata of Europe and North America. 



