Ice ami its Natural History 271 



glacier, however, the flow of the ice in all its parts continues: 

 but its effect outside of the glacier is almost if not quite nil. 

 In the stationary state its function in nature is conservation. 

 In the advancing state it adds the function of distribution. Its 

 destructive effect is very small. It protects the rock beneath 

 it from weathering, which is a chemical process, by the con- 

 stant maintenance of a low temperature and the practical 

 exclusion of the atmosphere. Any destructive action which 

 it exerts must therefore be mechanical. 



When two substances meet each other in mechanical strife 

 it is the harder that wears the softer, and in the strife between 

 rock and ice Nature makes no exception to this law. We 

 have seen from Hugi's description of a strife between rock 

 and ice which went on under his own eyes, what the effect 

 was on the ice, which was at a temperature much below that 

 of melting. In a week or two, however, the evidence of the 

 effect on the ice would be obliterated, great though it was, 

 while the reactive effect on the rock would remain, but it 

 is doubtful if it would be perceptible. In the battle between 

 ice and rock, the ice suffers much ; the rock comes out with a 

 scar or two. The scars abide, but the destruction disappears 

 and leaves no record ; hence the neglect of the major effect 

 and the exaggerated importance generally attached to the 

 minor. 



It has been said above that when the glacier begins to 

 advance, it performs a distributive function by digging up 

 and pushing before it the rock debris which it finds in front 

 of it in the valley. This debris consists partly of matter 

 which has been brought down by the glacier at some previous 

 time when its dimensions were greater, and partly from the 

 general wasting of rock on the faces of the mountains, which 

 form the sides of the valley. This is the source of the detritus 

 which gravitates surely into the valley, whether it be occupied 

 by glacier or river. The function of the river also is mainly 

 distributive: it has very little share in the duty of procuring 

 or shaping the pebbles in its bed. The stones in the river-bed 

 are furnished by the chemical process of weathering on the 

 rocks above. This loosens and separates, and, in many cases, 



