x 4° 
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 
