3° 2 



LEWIS G. WESTGATE 



IC«. rnorim-n 



Fig. 6. — Glaciated and jointed ledge. 



seems to have been above the ice-level, and to have been formed by 

 undercutting, or sapping, of that part of the Valley side above the 

 glacier surface. The ridges between some of the more vigorous 

 lateral valleys, as between Crystal Lake and Willis gulches, seems 

 to show this intermediate slope due to glacial sapping. The pre- 



glacial slope has been 

 destroyed by valley- 

 cutting, but the steep 

 slope of the upper glaci- 

 ated valley gives place to 

 a gentler, but still steep, 

 slope, which is best ex- 

 plained by glacial sap- 

 ping. The same element 

 in the valley slope is 

 shown in the upper angle 

 of the truncated spur in the main valley shown in Fig. 9. 



2. Glaciated surfaces. — Glacially smoothed surfaces are common 

 in the main valley, especially so on the rock-barriers and rock-bosses 

 which were peculiarly exposed to glacial erosion. In the matter 

 of abundance of glaciated surfaces there is a great difference between 

 the main valley and its tributaries. The larger lateral valleys, such 

 as Willis Gulch and Crystal Lake Gulch, have suffered an almost 

 complete destruction of their glacial surfaces. At one point on the 

 wall of Willis, glacial smoothing was recognized, and in Crystal 

 Lake Gulch a small area on the west wall, and a certain amount of 

 smoothing on the hummocky surface of the cirque floors, are all. 

 Some of the other gulches show even less remnants of glacial sur- 

 faces than do these two. Glacial striae are found only on the more 

 perfectly preserved surfaces in the granite of the main valley. 



A matter of importance is the proportional amount of erosion due to 

 glacial abrasion or glacial plucking. In almost all cases rock-ledges 

 and rock-bosses show a great difference between the stoss and lee ends. 

 The former are apt to be well-rounded; the latter, almost invariably 

 steep and coarse-hackly. The jointed structure of the granite in 

 the main valley is such as to favor plucking. The accompanying 

 figure (Fig. 6) of a glaciated ledge on the north side of the valley 



