GLACIAL DEPOSITS l6l 



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 



