254 DESCRIPTIVE GEOLOGY. 



SECTION IV. 



DESCRIPTIVE GEOLOGY OP THE MOUNTAIN REGION. 



■ 



NoETHEEN Slopes of the Uinta Range. — From Concrete Plateau to 

 Mount Corson the Mesozoic beds involved in the Uinta upheaval are, in 

 general, deeply buried beneath the Tertiary and post-Tertiary accumula- 

 tions of the Bridger Basin. The Tertiary beds, which attain an elevation 

 of over 10,000 feet, extend high up on the flanks of the ranges as far as the 

 Weber Quartzite, the lowest group of conformable sedimentary beds, which 

 form its core, so that, seen from the interior of the basin, the range presents 

 the appearance of a partially-submerged mountain-ridge. It is only in the 

 deeper canon-cuts of the streams flowing from the interior of the range that 

 the upturned edges of the Mesozoic beds may be observed, and here, even, 

 they are sometimes obscured, and their continuity broken by accumulations 

 of gravelly material, glacial moraines, and debris of the Wyoming Conglom- 

 erate. In the eastern portion of this extent, the denudation has been greater, 

 and a proportionately larger extent of outcrops of these older formations 

 may be found. The siliceous limestone beds of the Upper Coal-Measure 

 group can, in general, be more easily traced, as, on account of the resisting 

 nature of their material, and the generally steep angle at which. they stand, 

 they have formed high, narrow ridges, which frequently project above the 

 horizontal Tertiary beds, thus affording a guide to the general direction of 

 the lateral flexures, which cause deviations from the general east and west 

 strikes of the formations involved in the uplift. The difficulty of tracing 

 the outcrops of the upturned beds is enhanced by the forest-covering, which 

 extends over the upper portion of the flat, terrace-like spurs, commencing 

 at an elevation of less than 9,000 feet, and stretching up to the bases of the 

 high, castellated, rocky ridges and peaks of the interior of the range. 



Along the steep banks of the canon-like valleys at the head of Black's 

 Fork, good exposures are found of the Triassic sandstones and the Permo- 

 Carboniferous and Upper Coal-Measure limestones. 



The ridge which forms the divide between these waters and those of 

 Bear River is, as we have seen, in its lower part, a comparatively level 



