300 EXTERNAL APPEARANCE OF GLACIERS. 
effort to force itself around the promontory, the 
ice was violently torn apart, and that the rent 
must take place in a direction at right angles 
with that in which the mass was moving. If 
the mass be moving inward and downward, the 
direction of the rent must be obliquely upward. 
As now the mass continues to advance, the cre- 
vasses must advance with it ; and, as it moves 
more rapidly toward the middle than on the mar- 
gins, that end of the crevasse which is farthest 
removed from the projecting rock must move 
more rapidly also ; the consequence is, that all 
the older lateral crevasses, after a certain time, 
point downward, while the fresh ones point up- 
ward. 
Not only does the glacier collect a variety of 
foreign materials on its upper surface, but its 
sides as well as its lower surface are studded 
with boulders, stones, pebbles, sand, coarse and 
fine gravel, so that it forms in reality a gigantic 
rasp, with sides hundreds of feet deep, and a 
surface thousands of feet wide and manv miles in 
%/ 
length, grinding over the bottom and along the 
walls between which it moves, polishing, grooving, 
and scratching them as it passes onward. One 
who is familiar with the track of this mighty 
engine will recognize at once where the large 
boulders have hollowed out their deeper furrows, 
where small pebbles have drawn their finer marks, 
