i 9 6 
ALASKA GLACIERS 
of wear below sea-level, and (4) to the parallelism of gla¬ 
ciers and rivers. 
THE SURFACE OF A GLACIER 
Evenness as Compared to Rock Floor .-—The parts of 
glaciers which came under my observation were the lower 
or distal portions, with surfaces usually less than 1,000 
feet above sea-level. In these lower parts the master 
characters of the surface are a forward slope in the direc¬ 
tion of flow and horizontality in the direction normal to 
the flow, the direction of flow being inferred from the 
courses of medial moraines. 
The configuration of the rock floors beneath the glaciers 
could not be directly observed, but it was possible to infer 
their general characters, with high probability, from what 
could be seen of the rock floors in front of the glaciers. 
Such rock floors are in all cases abandoned glacier beds, 
having been covered by the ice not only in Pleistocene 
times but, in many instances, in historic time also. As 
a rule these bared portions of the glacier troughs exhibit 
much irregularity. The fiords vary rapidly in depth; in 
places they are diversified by islands. The land troughs 
have hills and hollows; and other hills jut through the 
glaciers as nunataks. It is therefore believed that the 
bottoms of the glacier channels have in general consider¬ 
able inequalities. 
These irregularities are only slightly represented in the 
configuration of the glacier surface. The greater inequali¬ 
ties of the longitudinal profile of the bed are shown by 
cascades of the glacier, but inequalities of the cross-pro- 
file are rarely indicated by visible shapes of the ice, and 
bosses or hills hundreds (perhaps thousands) of feet high 
may fail to influence the surface. If the summit of a boss 
approaches the surface it produces crevasses, but the 
broader features of the surface contours are not changed. 
