Vol. 6] Beid: The Qi 'omorphogeny of the Sierra Nevada. 161 



its current swift, often torrential. In times of high water the 

 low land just west of the Virginia Range becomes a lake. Upon 

 entering its canon in the Virginia Range the river resumes its 

 rapid flow and downward cutting of the rocks of the bed. The 

 conditions of deep, sluggish water changes to that of rapids over 

 shallows within a few feet. The range here seems to be rising 

 faster than the river is able to cut. The axis of greatest eleva- 

 tion appears to be a few hundred yards only within the canon. 

 At this line some river deposits exist above the present water- 

 level, and some fresh- water shells are poorly preserved in a few 

 thin beds. This may indicate an earlier axis of elevation to the 

 east of the present one, with temporary damming of the river. 

 These observations, and those relating to the Carson River, estab- 

 lish the slow elevation of the Virginia Range and the antecedent 

 characters of the two streams. The terraces suggest a wealth of 

 facts yet to be ascertained relating to the late Pleistocene and 

 Recent geomorphic history of the region. 



Transmitted May 5, 1910. 



