THE 



JOURNAL OF GEOLOGY 



OCTOBER-NOVEMBER, 1904 



THE PROFILE OF MATURITY IN ALPINE GLACIAL 



EROSION.^ 



The literature of glaciation has not escaped the blemish of too 

 free generalization. It was early asserted of the Sierra Nevada, for 

 example, that Pleistocene glaciers of the alpine type, descending 

 from an ice- cap in the summit region of the range, had reached to 

 the range foot, and that the abnormally large canyons, particularly 

 of the western flank, were the products, from head to foot, of glacial 

 erosion. Such a statement made of southeastern Alaska, of the 

 Scandinavian peninsula, or of the Patagonian Andes woul(f not on the 

 face of it be absurd. Nor was it absurd of the Sierra Nevada. It 

 was possible, despite the low latitude, that ice-streams should have 

 descended to the range foot, and it was theoretically not impossible 

 that they should have excavated deep canyons. The matter, espe- 

 cially of glacier efficiency in erosion — a vexed question — is one mainly 

 of the evidences. It cannot safely be handled deductively; and it 

 need not be, since in glaciated mountains the evidences crowd the 

 field. But the announcement was unscientific, because unsupported 

 by facts of observation. Its author had no right to make it. On 

 the other hand, it was no less unwarrantable and dogmatic to assert 

 the contrary, which also was freely done. 



My own acquaintance with the phenomena of glaciation of the 

 alpine type had its beginning in the Sierra Nevada, in 1883, in the 

 latitude of the Yosemite Valley — the so-called High Sierra. Pre- 

 vailing opinion as to that region, it appeared, ranged between the 



, iRead at the International Congress of Arts and Science, St. Louis, September 

 21, 1904. 

 Vol. XII, No. 7. 569 



