40 THE CANADIAN NATURALIST. [Feb. 



the Rhine, about which Gaul and German have contended since 

 the dawn of European history, is of similar origin. The mass of 

 material which has thus been carried off from the Alps, would 

 suffice to build up a great mountain chain. Thus by the action 

 of ice and water — 



" The mountain falling cometh to naught 

 And the rock is removed out of its place." 



Many observers who have commented on these facts have taken 

 it for granted that the mud thus sent off from glaciers, and which 

 is so much greater in amount than the matter remaining in their 

 moraines, must be ground from the bottom of the glacier valleys, 

 and hence have attributed to these glaciers great power of cutting- 

 out and deepening their valleys. But this is evidently an error, 

 just as it would be an error to suppose the flour of a grist-mill 

 ground out of the mill stones. Glaciers it is true groove and 

 striate and polish the rocks over which they move, and especially 

 those of projecting points and slight elevations in their beds, 

 but the material which they grind up is principally derived from 

 the exposed frost-bitten rocks above them, and the rocky floor 

 under the glacier is merely the nether mill-stone against which 

 these loose stones are crushed. The glaciers in short can scarcely 

 be regarded as cutting agents at all, in so far as the sides and 

 bottoms of their beds are concerned, and in the valleys which the 

 old glaciers have abandoned, it is evident that the torrents which 

 have succeeded them have far greater cutting power. 



The glaciers have their periods of advance and of recession. 

 A series of wet and cool summers causes them to advance and 

 encroach on the plains, pushing before them their moraines, and 

 even forests and human habitations. In dry and warm summers 

 they shrink and recede. Such changes seem to have occurred in 

 by-gone times on a gigantic scale. All the valleys below the pre- 

 sent glaciers, present traces of former glacier action. Even the 

 Jura mountains seem at one time to have had glaciers. Large 

 blocks from the Alps have been carried across the intervening 

 valley and lodged at great heights on the slopes of the Jura, lead- 

 ing the majority of the Swiss and Italian geologists to believe that 

 even this great valley and the basin of Lake Leman were once 

 filled with glacier ice. But unless we can suppose that the Alps 

 were then vastly higher than at present, this seems scarcely to be 

 physically possible, and it seems more likely that the conditions 

 were just the reverse of those supposed, namely, that the low land 



