338 DESCEIPTIVE GEOLOGY. 



fragments of feldspar and quartz grains, with thin laminae of dark biotite 

 plates and some bronze-colored mica. 



On the west side of Bear Eiver, the Tertiary beds conceal all the 

 underlying formation, the river itself, as far as the Narrows, running in a 

 narrow valley of fluviatile Quaternary. Below the Narrows, this valley 

 expands into an open level country, from 4 to 6 miles in width, entirely on 

 the west side of the stream. On the east side, from the Narrows northward 

 beyond the limits of our map, heavy dark-blue limestones come down 

 to the water's edge in steep precipitous slopes, which present a rugged 

 broken surface cut through by deep rough canons. The formation rises 

 some 2,000 feet above the river, extending to the eastward in irregular 

 undulating ridges until concealed beneath the Tertiaries. At the Narrows 

 the limestone falls off abruptly, the beds standing nearly vertical, and, on 

 the west side of the river, the Vermillion Creek beds come close up to the 

 limestones. The river, which has run due north for a long distance, is 

 curiously deflected on reaching the limestone, and takes a due west course 

 for 5 or 6 miles, then bending sharply to the north again, hugs closely the 

 flanks of the hills. But little opportunity was afforded for the examination 

 of this somewhat isolated body of limestone, and it has been referred to the 

 Upper Coal-Measure limestone, on no palasontological or direct stratigraph- 

 ical evidence, but solely from its relative position with regard to the Silurian 

 and Cambrian bodies on the west side of Bear River Plateau. 



The greater part of Bear River Plateau is covered with a considerable 

 thickness of the Vermillion Creek beds, which are here in general rather 

 coarser, and more conglomeratic than those of the Aspen Plateau. Its sum- 

 mit varies in width from 2 to 4 miles, beyond which to the eastward these 

 beds are well exposed by the deep canons of Woodruff, Randolph, and Sal- 

 eratus Creeks. They lie inclined at an angle of 1° to 2°, and a probable 

 thickness of 2,000 to 2,800 feet is exposed in the canons. They exhibit 

 considerable differences in their lithological habit, but are characterized by 

 a prevailing reddish-gray tint and coarse arenaceous texture. Most of the 

 beds would be denominated sandstones, the fragmentary material being 

 too small to be classed as a conglomerate. There are occasional beds of 

 white sandstone, but even these are more or less stained by oxide of iron, 



