156 ALASKA GLACIERS 



be ascribed to unequal deposition of drift, but there is 

 reason to believe that much of the inequality pertains to 

 the rock floor and is to be ascribed to glacial erosion 

 as conditioned by varying resistance of the terrane. A 

 number of islands and one long peninsula are so placed 

 that they may properly be regarded as portions of the 

 trough bottom which rise too high to be covered by the 

 sea. They are of rock, are thoroughly glaciated, and their 

 axes, as well as all flutings and other lines of sculpture, are 

 parallel to the fiord walls. Ice erosion has gone so far as 

 to destroy all semblance to the forms characteristic of 

 aqueous sculpture. Several islands and the southern 

 part of the peninsula are shown in figure 3, and the view 

 in figure 75 was made from the summit of the penin- 

 sula, 1,750 feet above sea-level. 



From these various facts, as well as from general im- 

 pressions to which it is not easy to give definite expres- 

 sion, I would draw the following tentative inferences : The 

 V-gorges at the heads of branches of Lynn Canal and in 

 the uplands bordering the canal, were made chiefly by 

 pre-glacial streams, and they have been but moderately 

 deepened by glaciers. There was a pre-glacial, com- 

 paratively narrow, valley through Lynn Canal, the floor 

 of the valley being below present sea-level and related to 

 a low base-level. Lateral V-gorges were tributary to 

 this and were largely adjusted to it in grade. The Pleis- 

 tocene glacier broadened the river valley, truncated the 

 side spurs and the tributary gorges, and at the same time 

 materially deepened the valley for the whole breadth of 

 the trough. The glacial degradation is conceived as 

 averaging hundreds of feet and possibly more than one 

 thousand. 



The lateral valleys so situated as to carry glaciers under 

 other than Pleistocene conditions, are thoroughly shaped 

 in characteristic U forms, and they now contain glaciers. 



