﻿170 J. LeConte — Elevation of the Sierra Nevada. 



duced at the beginning of the Quaternary — we now proceed to 

 give further evidence. 



Mr. Russell, in a recent very excellent and suggestive paper 

 on Southern Oregon,* has shown that the country rock of this 

 region consists wholly of successive sheets of lava several 

 thousand feet thick, originally level, but now broken by N". and 

 S. fissures into oblong blocks, which are mostly tilted in such 

 wise as to produce a series of faults, the uplifted sides forming 

 ridges while on the downthrows have accumulated lakes. This 

 is shown in fig. 9. In all cases the faults are normal, and there- 

 fore when the fissures dip in opposite directions, the wedge- 

 shaped blocks thus produced may drop bodily down, or be 

 raised bodily up, as shown in fig. 10, according as the base of 



Section showing Basin region structure. After Howell. 



Sketch sections across Warner valley. After Russell. 



10. 



SkiuM-ts. 



Sketch section across Stein Mts. After Russell. 



the wedge is upward or downward. We have in this region 

 therefore, on a smaller scale but in very simple and perfect con- 

 dition, the characteristic Basin structure, except that only in this 

 case the country being in the region of the great lava-flood, the 

 broken and displaced layers are lava-sheets instead of sediments. 

 As to the age of these faults, although he acknowledges some 

 discrepancy in the evidence derived from vertebrate and inver- 

 tebrate fossils, Mr. Russell decides with great positiveness that 

 the old or enlarged lakes of which the present lakes are the resi- 

 dues belong to the same period as Lake Lahontan and Lake 

 Bonneville, i. e. to the Quaternary. The fissures were therefore 

 formed and the displacements commenced at the beginning of 

 the Quaternary, doubtless by the same orographic movement 

 which so greatly increased the elevation of the Sierra. 



I have referred above to the supposed discrepancy between 



* U. S. Geol. Rep., 1882-'83, p. 435. 



