38 



miles in width, is bounded on the west side by a range of low mountains, 

 whose summits are well-timbered. The valley is excavated at an acute angle 

 to the strike of the strata, so that, as far as the eye can reach to north and 

 south, successive hog-bacUs issue, en echelon, from the western side, and run 

 diagonally, striking the eastern side many miles to the southward. At the 

 cafion of the Fontanelle, six of these hog-backs occupy the valley, and the 

 number varies as we proceed down the valley. The structure changes from 

 the same cause, as we explore in either direction. The dip of all these hog- 

 back strata is, to the west and sligiitly north, less steep at the eastern side, 

 but reaching 45°, and a still higher angle at the middle and west side of the 

 valley. There appears to be an anticlinal near the base of the eastern range, 

 which has been deeply excavated ; from its western slope (in the valley), the 

 upper beds, seen in the eastern range, have been carried away, leaving only 

 probable Triassic and Carboniferous strata exposed. In one of the latter, I 

 found a well-marked horizon of carbonaceous shales, extending as far as I 

 explored them. Toward the western side of the valley, the descending strata 

 are sandstones, but, whether identical with that of the eastern hills of Creta- 

 ceous age, I could not ascertain. Lower down the valley (to the south), 

 similar beds form a high, vertical wall of very light color, the scenery resem- 

 bling that of the Garden of the Gods in Colorado. I suspect that the exist- 

 ence of more than one fold can be demonstrated in these hog-backs and 

 mountains. 



The result, which bears on the history of the Bear River group, is, that, 

 on this side of the Green River basin, the Bitter Creek epoch is either want- 

 ing, or represented by a thin layer of red quartzite (or, perhaps, Cretaceous 

 No. 1), and that no coal of Cretaceous age exists along its western rim. 

 After following the valley to Ham's Fork River, and proceeding a short dis- 

 tance along it, toward the southeast, I crossed a thin bed of coal in the 

 upturned edges of the same beds crossed in the valley above. The discovery 

 of the extension of the fish and insect beds sixty miles north of the principal 

 localities is a point of interest in Tertiary geology. 



The Ham's Fork Mountains form the divide between the waters of Green 

 and Bear Rivers, respectively, and is passed by the Union Pacific Railroad at 

 and west of Aspen station, as is described by Dr. Hay den (Annual Report 

 for 1870, p. 149). He here points out that the distinctness of the two basins 

 was marked during the Tertiary [jcriod. and lieuce names the deposits of the 



