ALASKA GLACIERS 
I S° 
groove and are there gathered into trunks which follow 
the groove lengthwise till escape is found through some 
break in the ridge. The surfaces of trunks and tributaries 
are mutually adjusted where they join, but it is easy to 
imagine that the progressive erosion of their beds is re¬ 
lated to the volumes of the glaciers, and that the greater 
ice streams have the deeper channels. It is interesting 
to note in this connection that the bottom of this trough 
is below present tide-level — at least in part—in spite of 
the fact that there has here been a post-Pleistocene eleva¬ 
tion of land. Figure 74 shows a portion of the trough 
where it is occupied partly by glaciers and partly by an 
arm of the sea. The observer stands on the foothill ridge. 
Lituya Bay has the form of a letter T, the cross-bar ap¬ 
pearing in the view, and the shaft running through the foot¬ 
hills at the right. The large glaciers in the distance and 
foreground reach the longitudinal groove from deep 
mountain gorges. A small glacier, whose end barely 
touches the water, cascades over a sill that may be 800 
feet above tide. A hanging glacier at 2,000 feet or more 
sends a tongue down a shallow groove in the steep wall 
of the fiord. And, at the extreme left, a pocket glacier 
occupies a hanging valley at an altitude of 3,000 feet. 
The depth of the glacial excavation in the passages by 
Pitt and Princess Royal islands was probably about as 
great as in the passage by Vancouver Island. The scale 
of the topography is not far different, the evidence from 
hanging valleys is equally cogent, and the case is strength¬ 
ened by the presumption in favor of pre-glacial summit 
levels. Even with a low base-level it is not at all prob¬ 
able that pre-Pleistocene streams carried the erosion of 
any considerable part of these troughs below present sea- 
level, and the water partings within them may well have 
been a thousand feet higher. 
One of the more important passages of the Alexander 
