DEFORMATIONS. 



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Sacramento valley. This hardly seems j^ossible, 

 for we know of no such enormous mountains in 

 the country today. It seems much more probable 

 that the subsidence was not uniform. The Sacra- 

 mento valle}', which then undoubtedly existed, 

 flanked by the Sierra Nevada on one side and the 

 Coast range on the other, was a region receiving a 

 tremendous load of sediments from the moun- 

 tains on both sides. In accordance with the 

 isostatic condition of the earth's crust, it would 

 ])e expected that the loading region — that is, the 

 Sacramento valley — would sink, while the un- 

 loading region — that is, the Sierra Nevada and 

 the Coast range — would gently rise, and in this 

 way tlie enormous difference of elevation at the 

 close of tlie Shasta-Chico period would easily be 

 accounted for by supposing a much smaller origi- 

 nal difference at the beginning of that period. 



Relation of Knoxville and Mariposa Beds. 



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The Mariposa beds, as shown by Whitney and 

 others, are sometimes metamorj^hosed and in- 

 folded witli the Auriferous slates, which are un- 

 conformably overlain along the western base of the 

 Sierra Nevada by the Chico beds. Although the 

 Chico beds have not yet been found in contact 

 with tlie fossiliferous portion of the Mariposa beds, 

 their relation is such between Folsom and Mari- 

 posa that, according to Becker,* Turner and 

 Lindgren, there is no reason to doubt their 

 unconformity. This unconformity, as already 

 stated, can be traced around the northern end of 

 tlie Sacramento valley and along its western 

 border, where it passes successively beneath the 

 Horsetown and Knoxville beds. The Mariposa 

 and Knoxville beds, so far as yet known, occur 

 nowhere upon opjjosite sides of the great valley 

 within 30 miles of each other. There is good 

 reason to believe, however, from their relation to 



* U. S. Geol. Survey, Bulletin no. 19, p. 19. 



