EXTERNAL APPEARANCE OF GLACIERS. 299 
R mile oi more in length, and often measuring 
several hundred feet in width, the terror, not 
only of the ordinary traveller, but of the most 
experienced mountaineers. There is a variety 
of such crevasses upon the glacier, but the most 
numerous and dangerous are the transverse and 
lateral ones. The transverse ones were readily 
accounted for after the motion of the glacier 
was admitted ; they must take place, whenever, 
in consequence of the advance of the glacier 
over inequalities or steeper parts of its bed, the 
tension of the mass was so great that the cohe- 
sion of the particles was overcome, and the ice 
consequently rent apart. This would be espe- 
cially the case wherever some steep angle in 
the bottom over which it moved presented an 
obstacle to the even advance of the mass. But 
the position of the lateral ones was not so easily 
understood. They are especially apt to occur 
wherever a promontory of rock juts out into 
the glacier ; and, when fresh, they usually slant 
obliquely upward, trending from the prominent 
wall toward the head of the glacier, while, when 
old, on the contrary, they turn downward, so 
that the crevasses around such a promontory are 
often arranged in the shape of a spread fan, 
diverging from it in different directions. When 
the movement of the glacier was fully under- 
stood, however, it became evident, that, in its 
