HE YOSEMITE. 2G9 



studies, the leaders among the ranks of the glacialists fell 

 into another error equally great by their non-appreciation 

 of the fact that the present glaciers are only the weaker 

 representatives of ice masses which, up till a very recent 

 date, have occupied the same thalwegs and valleys. This 

 error in turn was the result of environment. Whereas the 

 error of the " non-glacialists " had arisen mainly through 

 lack of observations in space, that of the "glacialists " arose 

 through lack of appreciation of the sequence of events in 

 stream action. They simply took glacial corrasion as they 

 found it and assumed that, as now, so glaciers must always 

 have worked. But by reason of such error they found 

 themselves unable to answer the objections of the " non- 

 glacialists." " How," asked the latter "is the idea of the 

 overdeepening of valleys, the formation of lake and fiord 

 basins, the facetting and removal of valley spurs by ice 

 action to be reconciled with the knowledge that present- 

 day glaciers appear least competent at just those spots 

 where they should have been most energetic on the hypo- 

 thesis of ice erosion." "How," said they, "can a glacier 

 be said to have excavated a fiord basin when it may be seen 

 overriding its moraine lying in the fiord basin; how be said 

 to have made wide embayments in a valley when tliose 

 very embayments are to day occupied by uncompacted 

 moraine terraces; how be said to have quarried the 

 mountain sides when they to day only scratch, abrade, or 

 pass gently over a rock surface ; how have cut the valley 

 floor down for several thousands of feet when the roches 

 moutonnees dotting that floor show abraded surfaces up- 

 stream only, the downstream faces being frequently not 

 even scratched ; how have overdeepened canons for 

 thousands of feet when no moraines have been left there 

 to evidence the destructive action ; or how be said to have 

 been such engines of destruction when they yield now only 

 as flow by abundant crevassing, by shearing action of the 



