208° ELEMENTARY GEOLOGY 
the glacier, hundreds or perhaps thousands of feet in 
depth, drags the materials along. On account of the 
weight of the ice above, it acts like a sandpaper, 
pressing down with great force. 
Fia. 112. 
Rock over which a glacier has moved, forming glacial striz. 
So the rock of the glacier bed may be carved and 
‘polished, while the fragments themselves are thor- 
oughly ground. Rocks over which ice has moved, 
(Figs. 112 and 268), and pebbles that have thus been 
dragged along (Fig. 115), are often striated by this 
