SNOW AND ICE. 
103 
sensation of complete repose to the eye, the snowy 
white with an occasional tinge of the most delicate 
pink, make up a scene of which no picture or photo- 
graph can give more than a very inadequate impres- 
sion, and form an almost irresistible attraction to all 
true lovers of nature. 
The snow would accumulate and increase in 
thickness indefinitely if it were not removed, (1) by 
melting and evaporation, (2) by avalanches, and (3) 
by slow descent into the valley. 
Avalanches. 
Avalanches may be divided into two principal 
classes; dust avalanches, and ground avalanches. 
Dust avalanches generally occur after heavy snow- 
falls and in still weather, because the snow ac- 
cumulates on steep slopes until it finally gives way; 
first in one place and then in another; first slowly, 
then more rapidly, until at last it rushes down with 
a noise like thunder. 
The falling mass of snow compresses the air, 
and makes a violent wind, which often does more 
mischief than the actual avalanche itself. A great 
part of the snow rests at the foot of the declivity 
from which it falls, but a part is caught up by the 
wind and carried to a considerable distance. Such 
