EARLIER TERTIARY (EOCENE AND OLIGOCENE). 



767 



Generalized section of coal-bearing rocks in western portion of tJie Little Snake River coal field, 



Wyoming. 



"The three lower members of the upper coal group have the stratigraphic position of the "Upper Laramie "of 

 A. C. Veatch (Coal fields of east-central Carbon County, Wyo.: Bull. U. S. Geol. Survey No. 316, 1907, pp. 244-260). , 



Osborn correlates the upper part of the section in the Washakie Basin as later 

 Eocene, Uintatherium and Eobasileus zones. The strata are largely volcanic ash. 

 The lower zone (250 feet) is widely distributed. The upper zone (250 feet or more) 

 is restricted to Haystack Butte and the surrounding badlands. 



E. E. Smith ''^^ gives the following section of the Tertiary in southern Wyoming, 

 on the eastern margin of the large area mapped as Eocene. (See Chapter XV, 

 p. 680, for the Cretaceous section.) 



The Great Divide Basin coal field is situated along and north of the Union Pacific Rail- 

 road in south-central Wyoming and embraces portions of the northeast end of Sweetwater 

 County, the northwest end of Carbon County, and the southeast corner of Fremont County. 



^ ^ -fC *lC ?fC Jp Jp 5p ^ 



The coal-bearing rocks of the area here described are of Upper Cretaceous and Tertiary 

 ages. They consist of the Colorado, Montana, Laramie, undifferentiated Tertiary, and Wasatch 

 formations. Of these, only the last four contain workable coal beds. Thin beds of coal occur 

 in the basal portion of the Colorado, but at no place within the area treated do they reach min- 

 able thickness. The coal-bearing formations show considerable change in character from the 

 southern to the northern edge of the field. Those of the Cretaceous system thin rapidly toward 

 the north and the outcrops of the beds of the undifferentiated Tertiary become more and more 

 narrow, owing to the overlap of Wasatch conglomerate. The accompanying section shows 

 the thickness and general characteristics of the coal-bearing formations near the Union Pacific 

 Railroad and in the gap between Wliisky Peak and the Ferris Mountains. 



