878 M. Agassiz on Glaciers, Moraines, and Erratic Blocks. 



This accumulation of ice above all the hydrographic basins 

 of Switzerland may easily be supposed, on reflecting that when 

 lakes are once frozen to the level of their emerging cun-ent, the 

 running waters no longer drain off", and those of the atmosphere, 

 augmented by the vapours of the southern regions, which, un- 

 der the circumstances, abundantly precipitate themselves to- 

 wards the north, must have most rapidly augmented the extent, 

 and raised the level even to the height which has already been 

 established by the foregoing facts. The winter of Siberia was 

 for a time established upon a soil pi'eviously covered with luxu- 

 riant vegetation, and peopled with great Mammalia, whose fel- 

 lows in our day inhabit the warm regions of India and Africa. 

 Death enveloped nature in its winding-sheet, and the cold reach- 

 ing its extremest limit, gave to this mass of ice, at the maximum 

 of tension, the greatest hardness it could acquire. When any 

 one has frequently witnessed the congelation of a lake, he can 

 then form a conception of the vast resistance of ice in this con- 

 dition, and to what immense distances hard bodies which are 

 thrown upon its surface may glide in consequence of even a 

 feeble impulse. 



The appearance of the Alps, the result of the greatest con- 

 vulsion which has modified the surface of our globe, found its 

 surface covered with ice, at least from the North Pole to the 

 shores of the Mediterranean and Caspian Seas. This upheav- 

 ing, by raising, breaking, and cleaving in a thousand ways, ' e 

 rocks which compose the prodigiovis mass that now forms the 

 Alps, at the same time necessarily raised the ice which covered 

 them ; and the debris detached from so many deep upbreakings 

 and ruptures, naturally spreading themselves over the inclined 

 surface of the mass of ice which had been supported by them, slid 

 along the declivity to the spots where they were arrested, with- 

 out being worn or rounded, since they experienced no friction 

 against each other, and even when arrested came in contact 

 with a surface so smooth ; or after being stopped, they 

 were conveyed to the margin, or to the clefts of this im- 

 mense sheet of ice, by that action and those movements 

 which characterise congealed water when it is subjected to 

 changes of temperature, in the same manner as the blocks 

 of rock Avhich fall upon glaciers, approach their edges in 



