THE FORMATION OF GLACIERS. 
223 
fore ice is viscid because it moves. We shall 
see hereafter that the phenomena exhibited 
in the onward movement of glaciers are far 
more diversified than has generally been sup- 
posed. 
There is no chain of mountains in which the 
shape of the valleys is more favorable to the for- 
mation of glaciers than the Alps. Contracted 
at their lower extremity, these valleys widen 
upward, spreading into deep, broad, trough-like 
depressions. Take, for instance, the valley of 
Hassli, which is not more than half a mile wide 
where you enter it above Meyringen ; it opens 
gradually upward, till, above the Grimsel, at the 
foot of the Finster-Aarhorn, it measures several 
miles across. These huge mountain-troughs form 
admirable cradles for the snow, which collects 
in immense quantities within them, and, as it 
moves slowly down from the upper ranges, is 
transformed into ice on its way, and compactly 
crowded into the narrower space below. At the 
lower extremity of the glacier the ice is pure, 
blue, and transparent, but, as we ascend, it ap- 
pears less compact, more porous and granular, 
assuming gradually the charactei of snow, till in 
the higher regions the snow is as light, as shift- 
ing, and incoherent, as the sand of the desert. 
A "snow-storm on a mountain-summit is very dif- 
ferent from a snow-storm on the plain, on ac- 
