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Sierra Club Bulletin 



ice erosion which one may readily recognize at a glance. In 

 the High Sierra such evidences are conspicuous, indeed they 

 fairly leap to the eye; but lower down on the flanks of the 

 range they become progressively dimmer until at last they all 

 but fade away. The Yosemite region, as fate would have it, 

 lies in this very zone of increasing obscurity. At its head 

 glacial signs are plain enough, but toward its lower end they 

 become so faint as to be easily overlooked. No wonder that 

 opinions have varied widely regarding the glacial history of 

 the valley and still more so about the extent to which it has 

 been remodeled by the ice. 



Naturally it seemed of prime importance to the investiga- 

 tors last year to make an effort to settle this question of ice 

 erosion in the Yosemite Valley, to establish definitely how far 

 the ice advanced and, if possible, how much excavational work 

 it achieved. The physiographer of the party accordingly de- 

 voted the better part of his time to a search for ice signs. 



The manner in which he went about it may be of some in- 

 terest. Other investigators have relied in no small measure 

 upon topographic indices for the determination of the limits 

 of the ice as well as for a measure of its erosional work. The 

 sculpture of the Yosemite region, however, is notably erratic 

 and as an index of ice erosion quite deceptive (for reasons 

 that will become apparent later) ; besides it is to be borne 

 in mind that there was not only one ice age, as it is popularly 

 termed, but several ice epochs, the glaciers of which differed 

 greatly in extent and eroding power. The matter is there- 

 fore much more complicated than at first it seems. For these 

 reasons the writer deemed it wiser to regard the topography not 

 as a source of information but as one of the mysteries to be 

 explained. His plan was first to trace out the glacial 

 moraines, that is, the ridges of ice-transported debris that ac- 

 cumulated along the margins and at the fronts of the ancient 

 glaciers. Previous visits had shown him that deposits of this 

 sort are abundant and fairly well preserved in many parts 

 of the Yosemite region. By mapping them systematically on 

 the large-scale map of the valley, he hoped to be able to es- 

 tablish the exact outlines of the ice streams, and thus to lay 

 a sound foundation for further glacial research. 



