THE DKY MOUNTAINS. 207 



continuation of the great monoclinal ridge of Carboniferous sandstone north- 

 east of Po Canon, but, in fact, these mountains are made up of beds of Ter- 

 tiary Age, though there are outcrops of Mesozoic beds in the depths of the 

 deeper gulches. 



This range marks the continuation of the displacement that I have 

 called the great Uinta fault, and the evidences of the reverse movement are 

 complete. The first movement, which was upheaval on the Uinta side and 

 throw on the northeast side, seems to have been by monoclinal flexure, 

 while the last movement, which was throw on the Uinta side and upheaval 

 on the northeast side, was in part by flexure and in part by fracture. But 

 in the period of time separating the two movements the Brown's Park beds 

 were deposited across the zone of original flexure which had been greatly 

 degraded; still farther to the north west there is another line of displacement 

 approximately parallel to the first, with its throw also on the southwest side, 

 corresponding in this respect with the throw of the last displacement in the 

 Dry Mountain district. This northeast displacement fades out in a northwest 

 direction, and entirely disappears at the divide between the water-shed of 

 the Vermilion and the water-shed of the Snake River. When it is first seen 

 near this divide it is a gentle monoclinal flexure, and steadily increases in 

 abruptness along its line in a northeasterly direction until the bluffs of the 

 Snake River are reached, where it is seen as a dragged fault. There seems 

 to be no doubt that these displacements having throws to the southwest were 

 synchronous, while the evidence that the monoclinal flexure with throw to 

 the northeast was of earlier date is complete, for between the two periods 

 the Brown's Park beds were deposited that is, the Brown's Park beds are 

 seen to have been involved in the displacement having a southwest throw, 

 but took no part in the displacement with a northeast throw, as this last dis- 

 placement was made and the beds involved in it were truncated prior to the 

 deposition of the Brown's Park beds, and these beds were placed over their 

 upturned edges. 



In the Dry Mountains some interesting facts have been observed. 

 Along or near to the line of double or reverse displacements we sometimes 

 find an escarpment facing the southwest, composed of beds of the Bridger 

 period, or of still lower Cenozoic rocks, and dipping back toward the north- 



