DEAETH OF FOSSILS. 1 39 



evaporation of saline waters The degree of saline concentration which 

 the precipitation of gypsum indicates would be highly inimical to life 



The presence of the gypsum helps to account for the absence of life, 

 and the absence of life accounts for the brilliant color. The three promi- 

 nent characteristics of the formation are therefore quite in harmony with 

 each other. 



In passing now to the details of the exposures of the formation there 

 seems little need to linger. There is so great uniformity of relation and 

 structure that one or two local sections will illustrate the whole, while 

 nearly everything of importance has been anticipated by the description of 

 the several members and of the general topography. 



x4t the headwaters of the east fork of the Beaver the Red Valley is 

 1,000 feet higher than it is at Camp Jenney, fifteen miles farther south, and it 

 has a total elevation above the sea of about 5,000 feet. The purple lime- 

 stone is well exhibited all along the valley, rising to the eastward and lap- 

 ping against the side of the plateau, and near the head of the creek it covers a 

 considerable area The main stream and several tributaries from the east cut 

 through it to escape from the plateau to the Red Valley, and in their canons 

 excellent sections are exposed of the upper Carboniferous and the contiguous 

 Red Beds. The valley is here three or four miles in width, and its western 

 rampart — the Cretaceous and Jurassic foothills — is less prominent than 

 usual. To the southward Beaver Creek cuts a channel of increasing depth 

 into the red clay ; the Red Valley becomes narrower, and the western 

 escarpment becomes more pronounced, acquiring a height above the valley 

 of two or three hundred feet. In the vicinity of Camp Jenney and Fanny 

 Peak the purple limestone shows the double curvature represented in the 

 section. It laps steeply against the foot of the plateau, sometimes rising a 

 thousand feet or more above the valley. Then at the base it quickly curves 

 to the horizontal and in a mile or less it bends down again, disappearing 

 beneath the gypsiferous claj. Where it disappears its dip is 25° to i,0°, 

 and its eastern edge is upturned to 75° to 85°. Its thickness is 40 feet. 



Immediately east of Camp Jenney the lower red clay appears as a 

 soft sandy clay 50 or 75 feel thick, separating the purple limestone from the 



