206 ELEMENTARY GEOLOGY 
Rate of Movement. The rate of movement of the 
glacier is always very slow, and varies with the season, 
the slope of bed, the part of the glacier, and other 
conditions. It moves more rapidly in summer than 
in winter, and in the centre than on the margins. 
Fie. 110. 
Stream issuing from an ice cave in the Bowdoin glacier, Greenland. 
Usually the ice moves only one or two feet per day, 
though the Muir glacier traveis at the rate of about 
seven feet a day. So slow is the movement, that care- 
ful measurements must usually be made in order to 
detect it; but the ice stream flows on with constant 
