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University of California. 



[Vol. 3. 



all formed by the intersection of cirque slopes at points far below 

 the pre-glacial surface of the Summit Upland, as represented by the 

 remnants at the summit of Mt. Whitney and Sheep Mountain. 

 The general reduction of the altitude of the divide five miles in 

 length, between Whitney and Sheep Mountain, by this process, 

 has been certainly not less than 1000 feet for a belt three or four 

 miles wide; and this refers simply to the altitude of the crests 

 and not to the average reduction of the surface, which would be 

 much greater. In this reduction of the divide the latter has 

 clearly migrated westward, or away from the steeper side of the 

 mountains, for a distance of from half a mile to a mile. From 

 Sheep Mountain to Cirque Peak, the reduction and migration of 

 the divide have been effected by cirque aggression from the east 

 side only, the western side of this part of the range being ungla- 

 ciated for the most part. Looking north from Mt. Whitney, the 

 same reduction and migration of the summit divide is apparent 

 to an even greater degree. The recession of the eastern scarp of 

 the Sierra Nevada by the sapping of glacial cirques has left 

 Mt. Williamson an isolated stack, in the same sense that stacks 

 are left upon a wave-cut terrace by the recession of the sea-cliff. 

 The summit of this mountain is now a mile out from the ci'est 

 line at Mt. Tyndall, and half a mile out from the general line of 

 the summit divide. It has been severed from the main mass of 

 the mountains by cirque encroachment from the north. Lone 

 Pine Peak, which stands as an isolated mass over two miles from 

 the eastern scarp of the summit range, appears to be an even 

 more striking illustration of the recession of that scarp. 



In viewing from Mt. Whitney the revolution in the geomorphy 

 of the High Mountain Zone which has been wrought by ice sculp- 

 ture, and particularly by the gnawing of the cirques into the 

 heart of the mass, one cannot but reflect that, had glacial con- 

 ditions continued for twice as long as they actually did, or at 

 most three times as long, the entire summit tract would have 

 been obliterated, in the sense of being truncated to the level of 

 the cirque floors. It is interesting to reflect further that this 

 process of truncation, as it approaches completion, would not 

 only remove the mountain tops, but thereby, also, do away with 

 glaciation. Glaciation in the high mountains, in so far as it 



