322 DESCRIPTIVE GEOLOGY. 



more metamorpliism than in the eastern portions of the range, being gen- 

 erally white in color, and frequently of an almost vitreous texture. 



Between the heads of the Weber and Bear Rivers, the ridges are cov- 

 ered with Tertiary conglomerates and glacial debris; and few exposures of 

 beds higher than the quartzites, which form the core of the range, were 

 found. At the head of Bear River itself are evidences of more extensive 

 glacial action than at any point of the north slopes of the range. Here 

 terminal and lateral moraines are found along the broad valley, down to 

 within 10 miles of the railroad. 



The main fork of Bear River heads in a similar amphitheatre to that 

 of the Duchesne, but of somewhat less extent, under the northern slopes 

 of Mount Agassiz. The general character of these high glacial basins 

 and the effects of n^v^-erosion are seen in Plate X, which represents a view 

 of Mount Agassiz, taken from the shores of Lake Lai, the eastern of the 

 two little lakes at its northern base. This peak, which may serve as a type 

 of most of the peaks of the range, consists of a sharp wedge-shaped ridge, 

 whose summit is but a few feet in width, formed of horizontal beds of the 

 Weber Quartzite, which have been cracked and broken by the combined 

 action of sun and ice, and ground into fine sand by the trituration of its 

 falling masses. The enormous extent of the debris falling from one of 

 these peaks is shown in the talus-slopes along the northern face of the 

 peak. The summit of this peak is formed of a coarse white quartzite, 

 containing round pebbles, beneath which is a gritty zone 800 or 900 feet 

 thick, containing quartz up to the size of a hazel-nut, the general hue of 

 which is a pale green. Under this is a reddish-brown rock, containing 

 similar pebbles, with beds of slate and shaly sandstone. The mud and 

 shale beds are scarcely «,ltered, and closely resemble. the beds of the Con- 

 necticut River sandstone. Li the quartzites themselves are a few sheets, 

 never over 3 or 4 feet in thickness, of green slates, which contain a little 

 finely-comminuted mica. 



From the debris of the quartzite beds, on the ridge to the east of 

 Mount Agassiz, about 1,000 or 1,.500 feet below its summit, was obtained 

 a fossil, which, though not absolutely broken out from the quartzite beds 

 in place, would seem necessarily to have come from these beds, being 



