ICE AND GLACIERS. 117 



feet above the present level of the lake of Neufchatel. Similar 

 traces of ancient glaciers are found upon the mountains of the 

 British Islands, and upon the Scandinavian Peninsula. 



The drift-ice too of the Arctic Sea is glacier ice; it is 

 pushed down into the sea by the glaciers of Greenland, becomes 

 detached from the rest of the glacier, and floats away. In 

 Switzerland we find a similar formation of drift-ice, though on 

 a far smaller scale, in the little Marjelen See, into which part 

 of the ice of the great Aletsch Glacier pushes down. Blocks 

 of stone which lie in drift-ice may make long voyages over the 

 .sea. The vast number of blocks of granite which are scattered 

 on the North German plains, and whose granite belongs to the 

 Scandinavian mountains, has been transported by drift-ice at 

 the time when the European glaciers had such an enormous 

 extent. 



I must unfortunately content myself with these few refer- 

 ences to the ancient history of glaciers, and revert now to the 

 processes at present at work in them. 



From the facts which I have brought before you it results 

 that the ice of a glacier flows slowly like the current of a very 

 viscous substance, such for instance as honey, tar, or thick 

 magma of clay. The mass of ice does not merely flow along 

 the ground like a solid which glidas over a precipice, but it 

 bends and twists in itself; and although even while doing this 

 it moves along the base of the valley, yet the parts which are 

 in contact with the bottom and the sides of the valley are per- 

 ceptibly retarded by the powerful friction ; the middle of the 

 surface of the glacier, which is most distant both from the 

 bottom and the sides, moving most rapidly. Rendu, a Savoyard 

 priest, and the celebrated natural philosopher Forbes, were the 

 first to suggest the similarity of a glacier with a current of a 

 viscous substance. 



Now you will perhaps inquire with astonishment how it is 

 possible that ice, which is the most brittle and fragile of sub- 

 stances, can flow in the glacier like a viscous mass ; and you 

 may perhaps be disposed to regard this as one of the wildest 

 and most improbable statements that have ever been made by 



