330 DESCRIPTIVE GEOLOGY. 



of elevation may be considered to have marked the western Hmits of the 

 Eocene lake in which they were deposited. 



Along Bear River, from Bear River City to Evanston, the hills on 

 either side are occupied by the nearly horizontal beds of the Vermillion 

 Creek Eocene. On the east side of Bear River Valley, a short distance " 

 north of Evanston, the bluffs are formed of a series of coarse sandstones, 

 not differing- greatly in lithological habit from some of the beds of the Ver- 

 million Creek series. They are, however, more compact in general, and 

 dip from IS'' to 15° to the northeast, with a strike of north 25° to 35° west. 

 In these beds are valuable coal seams, one of which attains a thickness of 

 26 feet, which have been extensively worked by companies connected with 

 the railroad. A great number of fossil leaves have been obtained from beds 

 adjoining the coal, which have been considered by some fossil-botanists to 

 indicate rather a Tertiary than a Cretaceous horizon. There is, however, 

 no doubt, both from the stratigraphical position of the beds and their litho- 

 logical character, that they belong to the coal series of the Cretaceous, and 

 probably to the Laramie group; though, owing to the general indefinite- 

 ness of palseontological evidence and the isolated position of these beds, 

 the latter statement is only conjectural Within the mines, the dip of the 

 beds steepens considerably, attaining angles of 25°, and even 35°; and 

 the low dips at the surface, which have led some geologists to confound 

 them with the overlying Tertiaries, may be simply due to a settling-down 

 of the strata; the coal seam, which in the mine is 26 feet in thickness, for 

 instance, shows at the surface only one foot of clear coal. In the valley to 

 the east of the mines, as seen in the exposures of the stream-beds, the eastern 

 dip is continued, though on the slopes of Medicine Butte, which is the 

 highest point of the Aspen Plateau, there is some appearance of a westerly 

 dip in the strata. In the little canon to the south of Medicine Butte, how- 

 ever, the series of Cretaceous sandstones is seen at the forks to have a (Jip 

 of 45° to the northeast, and higher up, where they disappear beneath the 

 horizontal Tertiaries, there is apparently an even steeper dip. 



Region between Beae and Weber Rivers.^ — The region to the west 

 of Bear River, in the angle embraced between the Wahsatch and Uinta 



1 Prom field-notes ot Clarence King. ^ 



