Influence of Watev and Ice on the Earth's Features. 359 



can do, lofty mountains have struggled into existence, jagged 

 peaks and open valleys being formed, and the elevation being- 

 great enough to secure a temperature in which ice formed 

 in winter can accumulate from year to year, without being de- 

 stroyed by summer heat ? The circumstances under which ice 

 will thus become a part of the mountain system, must depend 

 on the climate of the locality ; but the ice once formed above, 

 will move down into the lower regions, and there continue to 

 advance till a balance is struck. 



Ice, under such circumstances, is a glacier. It moves, as 

 we have said, like a tenacious fluid, adapting itself in some 

 measure to the walls of rock within which it is shut in. But 

 it rubs both the walls themselves and the bottom over which it 

 passes ; for it is not only solid, but contains innumerable rocks 

 and stones, often large and heavy, and with these it erodes and 

 excavates to an extent and in a way which fluid water can never 

 accomplish. The motion is slow, but continuous. It is, however, 

 variable, and in different parts of the same glacier is often alto- 

 gether different. From a few inches to a few feet per day is an 

 ordinary rate. But with this motion it can carry away obstacles 

 very effectually, as is seen in the Alps and in all other glacier 

 mountains. 



We may well admit that ice can scratch and even tear up 

 and destroy rocks in moving over them ; but a mere study of 

 glaciers, as they now exist in Europe or even in the Himalayan 

 chain, would hardly enable us to understand what moving 

 rivers of ice are capable of doing under favourable circum- 

 stances. We must revert to geological observations to discover 

 this. In the Alps, where there is proof of glaciers having 

 existed formerly, whose extent in length alone was more than 

 fifty miles — when we see and measure the vast accumulation of 

 moraines or glacier- gravel, and the magnitude of the blocks 

 moved, we begin to understand that the force is a very active 

 one. But still it seems a bold assertion that ice, and ice alone, 

 has scooped out deep hollows, in some cases below the level of 

 the Mediterranean ; that the great lakes, not only those of Swit- 

 zerland and North Italy, but even those of North America, are 

 due to the same cause, and that generally we must look to ice 

 as having greatly helped to produce the existing physical 

 features of the temperate zones. 



It is objected to this view (1), that ice does not erode and 

 excavate, under ordinary circumstances, at its extremity, but, 

 on the contrary, sometimes rides over an ancient moraine with- 

 out removing it; (2), that it must, therefore, be yet more 

 powerless to excavate a deep hollow ; and (3) , that it must be 

 almost if not quite impossible that ice should first excavate 

 and then rise out of a deep hollow, on its way from the moun- 



