140 ALASKA GLACIERS 



mediate crest line is normally acute and serrate. The 

 association of steep slopes with rounded summits is an 

 abnormal condition requiring special explanation, and in 

 glaciated districts there is a strong presumption that the 

 rounding has resulted from the removal by ice of the 

 salient parts of the spurs. The rounding, therefore, serves 

 to show the extent of the district which has been subjected 

 to glaciation. It also affords a rough measure of the depth 

 to which the erosion has locally extended, for the imagi- 

 nation restores, more or less truthfully, the original sharp- 

 crested form, and thus realizes the difference between 

 that and the rounded form presented to the eye. 



In the district under consideration the work of round- 

 ing has been extensive. Below certain levels the crests 

 and profiles of hills, mountains and mountain spurs are 

 devoid of crags and sharp angles and have curved outlines. 

 From this general rule there are no deviations within the 

 range of our observation, except where it is evident that 

 the forms of glacial sculpture have been modified by later 

 work of torrents or breakers. The rounding is more 

 thorough at low levels than at high. Near its upper limit 

 it often amounts only to the removal of pinnacles and the 

 blunting of angles which would otherwise be sharp; 

 farther down it has not infrequently been carried so far 

 that no suggestion remains of the pre-glacial forms. In 

 many places the depth of rock pared away in the mere 

 smoothing of a rough topography must have amounted to 

 several hundred feet. 



The upper limit of rounding was estimated to range 

 from 3,000 to 5,000 feet in the region of the inside pas- 

 sage, and these estimates are in substantial agreement 

 with data given by the maps and photographs of the 

 Canadian Boundary Commission. From the latter I esti- 

 mate the height at 4,500 feet near Behm Canal (fig. 63) 

 4,000 feet near Berner Bay (fig. 62), 5,000 feet above 



