Lawson.] 



The Upper Kern Basin. 



361 



depends upon altitude, is, therefore, a process which automatically 

 terminates. 



The glacial reduction of mountain crests is equally well 

 exemplified on the summit of the Great Western Divide. Plate 

 43a shows a large cirque to the southwest of Sawtooth. The 

 The cirque floor descends by a series of hollow steps, each of 

 which holds a tarn. The configuration of the cirque appears to 

 be determined in a large measure by the orientation of the joint- 

 age. On the west side of the cirque is a belt of metamorphic 

 sedimentary rocks. Beyond the cirque may be seen the knife 

 edge divide which separates it from opposing cirques. In 

 Plate 43 b we have a view looking south along the crest of the 

 Great Western Divide from the summit of Sawtooth. In the 

 foreground are three cirques, that in the lower right-hand corner 

 being the same as that shown in Plate 43 a. The view is typical 

 for the divides between opposing cirques in this region, and 

 clearly illustrates the fact that such divides are due to the inter- 

 section of cirque slopes, and so proves the reduction of the main 

 divide by this process. The divide shown in the foreground of 

 this picture has been reduced not less than 1000 feet. In 

 Plate 44 a a glimpse is given of the upper wall of still another 

 cirque to the east of Sawtooth with the peak of Sawtooth 

 (12,345 feet) in the middle ground. The photograph is chiefly 

 useful as an illustration of the jointage of the granite and its 

 relation to the cirque wall. 



Not only are the mountain crests reduced by this opposition 

 of cirques, but plateaux are wholly or in part obliterated by the 

 same pi-ocess. In Plate 45 a is given a view of the plateau 

 remnant which lies to the west of Mt. Vandever, and at an alti- 

 tude of 11,200 feet. On the northern front of this plateau, as is 

 shown well in the photograph, there are no less than six shallow 

 cirques or glacial troughs, the rear walls of which have encroached 

 extensively upon the plateau and partly destroyed it. The general 

 horizontally of the sapping process in all six lines of attack is a 

 striking feature of the situation. Other glacial cirque-like 

 troughs scar the southern front of the escarpment in a similar 

 way; and the plateau itself is now but a narrow remnant. It is 

 easy to see that, if the process had been carried a little farther, 



