Hayden.] "^^ [Fobruarj' 19, 



quartz and feldspar, showing that the materials were derived at least 

 in part from the metamorphic rocks. Many of these sandstones disinte- 

 grate by exfoliation, or exquamation, and have the rusty sioherical concre- 

 tions scattered through them. 



The ma'n trend of these ridges is N. E. and S. W. The general ap- 

 pearance of the country is extremely desolate and cheerless ; scarcely 

 any vegetation but sage and grease-wood ; with here and there a little 

 lake, which from its alkaline character only adds to the dreariness of the 

 scene. 



Near the summit of the second ridge in the burnt rocks are quite 

 abundant impressions of plants ; and more especially lower down, about 

 the middle of the ridges, there is a layer of the iron rocks about 2 feet 

 in thickness largely composed of fragments of leaves. 



A few miles west of Fort Halleck a very conspicuous hill, called Sheep 

 mountain, is composed of carboniferous limestones, red beds ; and is 

 probably capped with lower cretaceous rocks. These beds incline 25°, 

 btit a very hard bed of sandstone capping the summit dips 35°. There 

 appears to be an unusual thickness of triassic (?) rocks at this locality. 

 The average dii) of the strata is from 30° to 50°, varying between west 

 and north. 



FIG. 2. 



From Medicine Bow river to Rattle Snake Pass, a distance of about 30 

 miles, the road extends through a monoclinal valley. * For nearly our 



* Fig. 2 illustrates the character of the upheaved ridges which everywhere are seen upon the 

 inargins of the mountain ranges, extending in many cases for miles, like waves; and the geologist 

 can walk across the upturned edges of all the formations from the granite to the most recent ter- 

 tiary ini-Iiisivp. 



