ALASKA GLACIERS 
158 
visit; they are known to me only through photographs, 
the contour maps of the Canadian Boundary Commission, 
and the soundings of the United States Coast Survey. 
As already mentioned, they are judged to be transverse 
to the strike, because they make wide angles with the 
general trend of the coast and because they are charac¬ 
terized by many short 
turns (fig. 80). Be¬ 
ing independent of 
strike, their courses 
are also independent 
of variations in rock 
texture, and this 
character makes 
them specially avail¬ 
able for the study of 
glacial erosion. 
Their walls are steep; 
photographs give the 
impression that they 
are decidedly steeper 
than those of Lynn 
Canal and its 
branches, but this 
fig. 80. mouth of speel river. impression is pos- 
The river is rapidly filling its deep trough with alluvium. gitfiy due tO the tend- 
Glacial rounding extends above the base of clouds, which ^ 
cut off the view at about 3,000 feet. ency of photOgraph- 
ers to select localities exhibiting bold scenery. The 
walls stand well apart, after the habit of glacial troughs, 
and exhibit notable parallelism (fig. 62). Hanging valleys 
abound,ranging in height up to 3,000 feet or more and being 
more numerous at the greater altitudes. Some, like the 
Stikine and Whiting, are occupied by rivers; others, like 
the Taku, Speel, Unuk and Skeena, contain rivers in their 
upper parts and admit the sea below; others, like Tracy 
