GLACIERS 199 
slowly moving ice stream in a valley. All over the 
mountain tops the snow falls, and wherever the slope 
is moderate enough to allow it to stand, it accumulates 
to great depths; but where the mountain is precipi- 
tous, the snow slides down into the valley, often in the 
Fia. 104. 
A snow field in the high Alps. 
Ms 
form of great avalanches. Some of the snow is also 
blown by the wind from the mountain tops into the 
valleys. 
As the mass of snow in the valley deepens, and 
becomes transformed to ice, it commences to flow’ 
1 Ice is commonly said to be viscous. Some object to this term and pro- 
pose ‘‘ plastic.’ Owing to the confusion which exists, it seems well not to 
use either term, but to say that it behaves like a viscous body, of which wax 
is a good example. Moreover, there seems to be little reason for doubting 
that ice really is viscous. 
