GLACIAL DEPOSITS 
161 
levels than at high is probably due to the concurrence of 
several causes rather than to a single one. First may be 
mentioned the difference in pressure. The rate of abra¬ 
sion, and of other forms of erosion, is probably enhanced 
by pressure, and during the height of the glacial flood all 
low-lying surfaces were subjected to greater pressure than 
those at higher levels. A second cause is connected with 
duration. The coming on and the passing of each Pleisto¬ 
cene epoch of glaciation was probably gradual, and there 
were doubtless glacial epochs of less intensity than the 
maximum. Thus the crests of low hills were subjected 
to glacial wear for longer periods than those of high spurs, 
and the difference may have been very great. Some al¬ 
lowance may also be made for subsequent modification at 
high levels. Ever since the last great ice flood began to 
wane, the valleys between high spurs have been occupied 
by small glaciers, and these have tended, by the develop¬ 
ment of their valleys, to reduce the width of the separat¬ 
ing ridges. Thus, while the rounding at low levels was 
still in progress, a work had been begun which tended to 
reduce the effect of the rounding at high levels. 
Glacial Deposits . — In the narrower parts of the inside 
passages we saw no accumulation of glacial drift. It is 
possible that drift masses were concealed here and there 
by the dense forest, but usually the spaces between cliffs 
and other visible outcroppings of rock were not large. It 
is probable that drift masses are concealed by the water, 
and have share in the production of the irregularity of the 
bottom; and a few bars and dams which are known to 
interrupt the continuity of other fiords are presumably 
morainic. As it is natural that the routes of travel should 
avoid such obstructions, it would be rash to infer the ab¬ 
sence of local moraines from our failure to observe them. 
The only important bodies of Pleistocene drift which we 
saw are on the shores of the Gulf of Georgia, where 
