FURTHER DISCUSSION AS TO ORIGIN 87 



sonal observation, that certain other isolated mountains in the Great 

 basin, as, for example, mount Newberry* Oregon, and Jeff Davis peak, 

 Utah, are similar to Stein mountain so far as their records of climatic 

 changes are involved, and, as is well known, are similarly situated in 

 reference to the Cascade range and the Sierra Nevada. 



RELATION OF PRE-GLACIAL EROSION TO HANGING VALLEYS 



It is exceedingly difficult to formulate and duly evaluate the evidence 

 just considered, but when it is correlated with other evidence, such, for 

 example, as the facts presented by Le Conte and others, showing the 

 occurrence of a Sierrian epoch of stream erosion preceding the Glacial 

 epoch, the only consistent conclusion seems to be that the Sierra Nevada 

 and Cascade ranges were deeply dissected by streams previous to their 

 occupancy by glaciers. 



In reference to hanging valleys, this conclusion favors the idea that 

 they have been excavated on the sides of pre-Glacial canyons, chiefly 

 because of the establishment of a baselevel of ice erosion in such canyons 

 by large valley glaciers, which determined the lower limit to which the 

 secondary glaciers on their sides could excavate, and does not favor the 

 idea that differential ice erosion should be held accountable for the 

 entire amount of discrepancy in depth between a receiving and its lateral 

 hanging valleys. 



FURTHER DISCUSSION OF ORIGIN OF GLACIATED HANGING VALLEYS 



As stated on a previous page, two classes of evidence may reasonably 

 be appealed to in seeking an explanation of the mode of origin of glaci- 

 ated hanging valleys. One of them, namely, the topographic changes 

 produced by excavation, has been briefly considered. The other, namely , 

 the character and distribution of the material removed in order to make 

 the excavation referred to and redeposited in recognizable form, remains 

 to be reviewed. 



If the hanging valleys of such mountains as the Sierra Nevada and 

 Cascade ranges are due to differential ice erosion, as claimed by several 

 geologists and geographers, it implies a vast amount of ice work. For 

 example, a conservative estimate of the volume of rock necessary to fill 

 the valley of lake Chelan up to the level of the hanging valleys on its 

 borders is in the neighborhood of 50 cubic miles. To perform a similar 

 task in several other valleys of the Cascade range and Sierra Nevada 

 would require the removal of similarly great quantities of material. Sev- 

 eral of these trunk valleys with hanging valleys along their sides are 40 



♦Mount Newberry is described and named in U. S. Geological Survey Bull. no. 252. 



