E. M. Deeley — Glaciers of the Yakutat Bay, Alaska. 81 



VII. — Glaciers of the Yakutat 1 Bay Rkgion, Alaska. 



By K. M. Deeley, Memb. Inst.C.E., F.G.S. 



rpHE United States Geological Survey has issued a paper, by 

 \_ Professor 11. S. Tarr, of Cornell University, on the Physiography 

 and Glacial Geology of the Yakutat Bay Region of Alaska. Here we 

 have high coastal ranges, culminating iu Mounts Cock and Seattle, 

 from which descend great glaciers to the sea, and also other glaciers 

 which come down to the waters of Russell Fiord. The whole region 

 shows signs of intense glaciation during quite recent times, and on 

 this account is an admirable area for the study of glaciers and 

 their work. 



That geology is still a living science is proved by the fact that 

 we are not yet quite agreed upon many important points. That 

 glacial geology is one of those matters about which there is at present 

 a great deal of difference of opinion will be seen by anyone reading 

 the Rev. Professor Bonney's Address to the British Association at 

 Sheffield last year. Of late years in this country many geologists 

 have been inclined to attribute very little erosive power to glaciers. 

 A few, on the other hand, are of opinion that glaciers are quite 

 powerful eroding agents, and consider that they have deepened 

 valleys, excavated many lake-basins, and produced physical features 

 which the ordinary atmospheric influences are now rapidly modifying. 

 Under these circumstances the views formed by Professor Tarr, after 

 a thorough study of a most instructive region, should be of considerable 

 importance. 



Although Russell considered that glaciers took immediate possession 

 of the Yakutat region as it rose from the sea, Tarr, after a more 

 thorough survey, considers "that there was profound denudation 

 before the glaciers took possession of the region is indicated by the 

 truncated folds and by the valley system in the peninsula, which 

 is distinctly a system of mountain drainage lines, later occupied and 

 profoundly deepened and broadened by ice". 



Professor Tarr, after dealing in detail with all the main valleys, 

 their glaciers, and the variable nature of their advances and retreats, 

 as evidenced by the observations of previous explorers and the deposits 

 they have left behind them, comes to the following conclusions: — 



" Of all the hypotheses proposed, glacial erosion alone appears 

 capable of explaining all the facts. It accounts for the broadened and 

 greatly overdeepened main valleys, with truncated spurs, spurless 

 walls, steepened slopes, and immature drainage lines ; the (J shape of 

 the hanging tributary valleys ; the non-progressive, irregular discordance 

 in the hanging level of these ; the difference in erosion from place to 

 place ; the irregularities of the valley bottoms and the through valleys — 

 a combination of features which has never been described, except from 

 a region which has been, or still is, occupied by glaciers. 



"Against glacial erosion little has been urged further than the 



1 " The Yakutat Bay Piegion, Alaska : Physiography and Glacial Geology," 



by Balph S. Tarr : United States Geological Survey, Professional Paper 64. 

 4to ; pp. 184, 37 plates, 10 maps, and section. Washington, 1909. 



decade v. — vol. vm. — no. ii. 6 



