SOUTHERN FLANKS OF THE UINTA RANGE. 299 



West of Obelisk Plateau, the first good exposures of the Mesozoic beds 

 are found at the gateway-like entrance to Antero Canon, through which 

 flows the eastern branch of the Ute Fork. Between these two points, the 

 Upturned beds curve inward toward the centre of the range in a long, 

 rounded curve, the upper branches of the West Fork of Ashley Creek run- 

 ning in general with the strike of the beds, while at Antero Canon they 

 bend outward in a shai-p, narrow fold; in part obliquely, and in part trans- 

 versely, this canon has been cut through the beds involved in this fold, and 

 the section exposed presents some striking complications of structure, which, 

 taken by themselves, might look like nonconformities, except that, as is usual 

 in^ the Uinta uplift, the flanking and more recent beds stand at a steeper 

 angle than the older ones. 



The gateway of the canon, as of most of those of the southern slope, 

 is formed by the massive cross-bedded sandstones of the Triassic, which, 

 owing to their infrequency of bedding-planes, offer a greater resistance to 

 erosion, when inclined at a considerable angle, than even the harder siliceous 

 limestones of the Upper Coal-Measure group. On the eastern side of the 

 gateway were found about 1,500 feet of white and brown sandstones, stand- 

 ing at an angle of 70° south, in the upper part of which was a bed of bitu- 

 minous sandstone, like that found on the Wonsits Ridge, having the same 

 blackish-brown fracture and musky odor, containing, however, only 6 

 per cent, of carbonaceous matter, with 90 per cent, of silica. The 

 summit of the ridges on either side of the canon-gateway being formed 

 of horizontal beds of Tertiary, the outcrops along the slopes are fre- 

 quently concealed beneath their debris and cannot be followed continu- 

 ously; but in the soft slopes, at a higher geological horizon than the sand- 

 stones, were found some limestones included in argillaceous strata, from 

 which were obtained two undetermined species of Tancredia and an Astarte, 

 not in a very good state of preservation, but sufficient to determine the 

 horizon of the beds as Jurassic. Above these were ^ few indistinct out- 

 crops of sandstones, supposed from their position to be Cretaceous. On the 

 western side of the gateway, the outcrops of the same white and brown 

 sandstones could be seen under the horizontal Tertiaries, standing at an 

 angle of 60° south, below which were the red sandstones of the Triassic, 



