74 



a. F. BErKP:R — structure of the sierra NEVADA. 



the great valley is about northwest to southeast, and it would be natural to 

 suppose that the right line connecting the center of inertia of the eroded 

 area and the center of inertia of the sediments of the great valley would 

 strike at right angles to this trend. The strike of the thrust, on the other 

 hand, was determined at south-southwest to north-northeast. 



At present the rain-fall is far smaller towards the southern end of the 

 range than in its more northerly portion, and such, too, seems to have been 



Figure 13 — Forces involved in vphearni and subsidence. 



the case during the period of glaciation, for the glaciers were much less ex- 

 tensive to the south than to the north. During the Tertiary the greater 

 abundance of gravel to the northward is at least consistent with a similar 

 distribution of precipitation. Hence erosion was probably greater towards 

 the north. The deposits of the great valley, on the other hand, form an 

 almost level plain, seemingly the bottom of a shallow Tertiary gulf. 



It seems, then, that much of the material derived from the northern end 

 of the range must have moved down the valley to the southeast. This trans- 

 fer would evidently deflect the line of thrust towards the meridian. 



Thus the theory that the earth is a solid, highly viscous mass is in all 

 respects compatible with the observations, fully explaining every one of the 

 six fissure systems, the faults observed, and the enormous resistance to tilting 

 which the range has displayed. 



Washington, D. C, November, 1890. 



