*5 6 
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. 
