GLACIATION OF THE ALASKA RANGE 419 
The north side of the range is here unsurveyed, but it is reported 
that the glaciation is less extensive on that side than on the south. 
The glacial conditions east of the pass and on the north side of the 
Wrangell Mountains have already been briefly described.* 
One of the most striking features of the map (Plate I) is the 
great development of the glaciers on the southward slope of the 
range as compared with those on the north slope, especially in the 
vicinity of Mount McKinley. Two factors are believed to be 
responsible for this unequal distribution of glacial ice. Probably 
the most important of these is the greater amount of precipitation on 
the south slope. The moisture-laden winds from the Pacific in 
passing northward over the range drop most of their content as 
snow on the south slope. On the interior slope the precipitation 
is light, and as the amount of snowfall has a controlling influence 
in the growth and continued activity of glaciers, the southward- 
~ moving ice tongues have a great advantage over the poorly fed 
glaciers on the north. The second factor which favors the Pacific 
slope glaciers is the greater area of their accumulating grounds. On 
the south slope the average distance from the crest line to the base 
of the main range is more than 25 miles, while on the north it is 
only half this distance. The area of accumulation of those on the 
north slope is therefore much more restricted and the glaciers 
are correspondingly of smaller proportion. This unequal develop- 
ment of glaciers holds in other parts of the range as well, in the 
vicinity of Mount Hayes, and east of Delta River, in regions where 
there is not the same discrepancy in the area of the collecting fields. 
The advantage is here given to the:southward-moving glaciers by 
the greater snowfall on that side of the range. 
INFLUENCE OF GLACIERS ON THEIR VALLEYS 
The erosional effects of glaciers upon their valleys have been 
so frequently and so fully discussed by many writers that it is 
unnecessary to dwell upon them here in detail. The most notice- 
able results of this erosion are the development of the great U- 
shaped troughs, with the removal of the minor irregularities seen 
1S. R. Capps, ‘Glaciation on the North Side of the Wrangell Mountains, Alaska,” 
Jour. Geol., XVIII (1910), 33-57. 
