1809.] ^^ [Haydcn. 



entire route the road seems to form the line of separation between the 

 cretaceous and tertiary rocks, the former being well displayed on our 

 left, juttino- up against the mountain sides ; the latter extending in wave 

 like ridges into the distance on our right. As we approach Pass creek 

 however about 5 miles to the east, the cretaceous beds reveal themselves 

 clearly on the right side of the road, No. 5 attaining a great thickness ; 

 while, on the left, inclining from Sheep mountain Numbers 3 and 2 are 

 very plainly shown in a series of irregular and rather low ridges. All 

 along Elk mountain the red beds are visible but not conspicuous, and 

 they do not give color to the debris at the foot of the hills. In this 

 vicinity the tertiary beds must be at least 5000 feet thick, which, with an 

 equal thickness of the cretaceous, makes in all at least 18,000 feet, a 

 larger development than I know at any other point to the eastward. 

 Indeed we shall be able to show that these formations continue to in- 

 crease in thickness as we go west. 



On the north side of Pass creek we have an uplift of rather fine grain 

 yellow sandstone, which presents a front like a wall composed generally 

 of vertical columns. On the summit are isolated piles of every form, 

 the relics of erosion. The sandstone is about 200 feet in thickness and 

 the ridge inclines northward at an angle of about 19°. The trend of all 

 these ridges varies between north and west. 



As we emerge from the hills through the Pass on the Pass creek, we 

 strike a vast open plain, and the ridges of upheaval seem to pass off and 

 die out en echelon in the plain, the ends making a gentle flexure from 

 the west northward, so as to form one side or rim of the plain. There 

 appears to be in these formations many alternate beds of brownish yel- 

 low sand and sandstones, the whole readily yielding to atmospheric in- 

 fluences, covering the hills as well as the valleys, with a great depth of 

 fine sand, from which the long lines of harder sandstone project. These 

 ridges of upheaval run at various distances from each other, from 100 to 

 1000 yards, with monoclinal valleys intervening. 



The broad plain west of Elk mountain must be a region of depression; 

 or a portion of the country left undistjirbed while the surrounding parts 

 were elevated. As far as the eye cjin reach this plain appears to be per- 

 fectly level ; and no cuts to show the character of the underlying beds. 

 A thick deposit of drift covers every thing. On its northern side the 

 mountain ridges seem to trend about north-east and south-west, the 

 southern end sloping gently down with the plain. The rusty calcareous 

 sandstones which form the inner ridges facing the plain are undoubtedly 

 cretaceous and incline 30° to 45°. These rusty sandstones here form a 

 belt about 1^ miles in width, with intercalated layers of yellow arena- 

 ceous material covered with grass, only the harder layers projecting here 

 and there above the surface. In one of these higher ridges of sandstone 

 a Baculite {B. ovatus) was found. In another ridge was a seam about 

 six inches in thickness composed entirely of a small oyster about the 

 size, "though probably distinct from" 0. Congesta. In the plain country, 



A. P. S. — VOL. XI — E 



