X.] ICE AND ,ITS WORK. 159 



A number of pieces of ice, powerfully squeezed together 

 in a hydraulic press, are readily united into a solid lump, 

 or a single mass may be crushed, and the fragments built 

 up into a differently shaped body. In a similar manner, 

 when a glacier is forced over an obstacle, the ice, being 

 brittle, cracks and snaps, but the enormous pressure of 

 the sliding mass behind, squeezes it together again, and 

 regelation immediately heals the fractures. The glacier 

 therefore accommodates itself to irregularities in its bed, 

 not by virtue of any real plasticity, but by being succes- 

 sively fractured and frozen. Jn fact, by suitable means, ice 

 may be artificially moulded at will, as though it possessed 

 true plasticity ; and a similar operation is doubtless carried 

 on in nature. 



As it creeps down the valley, the glacier transports, from 

 higher to lower levels, any detrital matter that may happen 

 to fall upon its surface. From the neighbouring rocks, 

 fragments are constantly being loosened by atmospheric 

 agents, and these, sooner or later, tumble down upon the 

 glacier. In this way, a line of debris fringes each side of 

 the glacier, some of the stones being perhaps several tons in 

 weight. Such accumulations of detritus are known as mo- 

 raines ; and, as those which are now being described, occur 

 on the two sides of the ice-river they are distinguished as 

 lateral moraines. As the glacier moves along, the moraine- 

 matter is carried forwards, until, at length, it reaches the end 

 of the glacier ; and thus fragments of rock may be transported 

 down the valley, far from the heights above. The water 

 which issues from the melting ice, at the end of the glacier, 

 is unable to carry off this burden of stones which the ice has 

 deposited ; and, hence, we generally find, across the end of 

 the glacier, a confused heap of rubbish, known as a terminal 

 moraine. When two streams of ice unite, the lateral 



