114 SCENERY OF SWITZERLAND. 
tion the square will be distorted to the lozenge- 
shaped figure T i' . Fix your attention upon the 
diagonal T i of the square; in the lower position this 
diagonal, if the ice could stretch, would be lengthened 
to T’ i . But the ice does not stretch, it breaks, and 
we have a crevasse formed at right angles to T’ i’ . 
The mere inspection of the diagram will assure you 
that the crevasse will point obliquely upward.” 
a s S' c 
Marginal crevasses then arise from the movement 
of the glacier itself; transverse and longitudinal cre- 
vasses are caused by the form of the valley. If the 
inclination of the bed of a glacier increases, even if 
the difference be but slight, the ice is strained, and, 
being incapable of extension, breaks across. Each 
fresh portion as it passes the brow snaps off in turn, 
and thus we have a succession of transverse cre- 
vasses. In some cases these unite with the trans- 
verse fissures, thus forming great curved crevasses, 
