EVIDENCE PROM ALASKA 45 



" When it is considered that these fiords, being parallel to the coast, run athwart 

 the general movement of the ice from land to sea, the fact that their depth is 

 comparable with that of troughs lying in the direction of general movement is 

 certainly remarkable." (Page 147.) 



The absence of moraines or masses of drift over wide districts is noted 

 as follows : 



44 In the narrower parts of the inside passages we saw no accumulation of glacial 

 drift." (Page 161. ) " The glacial deposits we encountered are of trifling magnitude 

 collectively in comparison with the glacial erosion, of which we saw evidence, and 

 it was therefore inferred that the principal regions of deposition lay outside the 

 field of our observation, . . . and that its outer margin was beyond the present 

 line of coasts." (Page 162.) 



If the Alaskan glaciers could abrade their valle}^s during the Pleisto- 

 cene to enormous depths in the crystallines, then the erosional work was 

 so rapid and effective that it could not have stopped sudden^, but con- 

 spicuous recessional moraines should be left in even the higher valleys. 

 However, if the ice first cleared the stream valleys of weathered ma- 

 terials and subsequently simply slowly abraded the smoothed and firm 

 rocks, as glaciers do toda}% then there should be no massive moraines 

 in the higher valleys, and the facts are harmonious. 



Speaking of the ''inequality of glacial erosion," the author frankly 

 says: 



" The great work which it has seemed reasonable to ascribe to ice in the deep- 

 ening and widening of fiords and other troughs stands in striking contrast to the 

 feebleness of ice erosion in other places, which permitted, for example, the preser- 

 vation of the low peneplains of Annette island and the vicinity of Sitka. In the 

 one case the depth of the erosion is measured by hundreds of feet ; in the other by 

 tens." (Page 160.) 



The explanation then given of the supposed contradiction seems in- 

 volved and inconclusive ; but harmony would be secured, not merely in 

 respect to this difficulty, but with other difficulties, by abandoning the 

 idea of enormous ice-cutting anyw r here in Alaska. 



An anomalous irregularity of supposedly glaciated surfaces is ex- 

 plained by "plucking" (page 206) ; but this appeal to plucking to 

 explain rough surfaces which are assumed to have been deeply eroded 

 seems inconsistent with the following: 



" The work of rock sculpture accomplished by the middle and lower parts of a 

 glacier is performed chiefly by the processes of abrasion and plucking. ... If 

 the plucked blocks have originally stood as projections they may be broken away, 

 even if quite firm and flawless; otherwise it is probable that they can be removed 

 only if originally separated by joints or other structural partings." 



VII— Bull. Geol. Soc. Am., Vol. 16, 1904 



