GLACIAL EROSION' AND TRANSPORTATION. 271 



It is the opinion of the writer that the excavation of many 

 of the valleys of the Sierra Nevada began long previous to the 

 Quaternary, and are in fact relics of a drainage system which 

 antedates the existence of the Sierra as a prominent mountain- 

 range. 



Those who seek to account for the formation of the Yo- 

 semite and other similar valleys on the western slope of the 

 Sierra by glacial erosion should be required to point out the 

 moraines deposited by the ice-streams that are supposed to 

 have done the work. The glaciers of this region were so 

 recent that all the coarse debris resulting from their action yet 

 remains in the position in which it was left when the ice 

 melted. If the magnificent valleys referred, to are the result 

 of glacial erosion, it is evident that moraines of great magni- 

 tude should be found about their lower extremities. Observa- 

 tion has shown that debris piles of the magnitude and charac- 

 ter required by this hypothesis are notably absent. 



It is perhaps not disgressing too far to state that the 

 writer, while visiting the Yosemite, could not avoid adopting 

 an hypothesis advanced some years since by J. D. Whitney, to 

 the effect that the main characteristics of the valley are due to 

 dislocation ; or, in other words, that the orographic block be- 

 neath the valley has subsided. No facts were observed, how- 

 ever, conflicting with the conclusion of Clarence King that 

 the valley was occupied at least in part by glacial ice. The 

 majestic domes of the Yosemite region have not been rounded 

 by glacial action as some writers have supposed, but have been 

 produced by the weathering of granite, in which a concentric 

 structure on a grand scale was produced when the rocks were 

 in a plastic condition.* 



Another illustration of the anomalous erosive power of 

 glacial ice is seen in the so-called cirques so abundant in gla- 

 ciated regions containing mountains. Here, again, we are 

 under great obligations to Mr. Russell for his careful report 

 upon these features of the high Sierra. Little is to be added 

 to his discussion of the subject. 



* " The Quaternary History of Mono Valley, California," pp. 350, 351. 



