G4 M. Ch. Martins on the 



it, and often impresses on them a particular and characteristic 

 form. By destroying all the asperities of these rocks, they 

 level the surface, and give them a rounded form in front, 

 while, behind, they sometimes preserve their abrupt, unequal, 

 and rugged forms. It will be understood that the effect of 

 the glacier is exerted principally on the side turned towards the 

 amphitheatre from which it descends, in the same manner as 

 the piers of a bridge are more damaged in front than behind by 

 the ice carried down the river in winter. Seen at a distance, 

 a group of rocks rounded in this manner reminds the spec- 

 tator of the appearance of a flock of sheep ; hence the name 

 roches moutonnees given them by Saussure, and which has 

 continued to be applied to them. 



3. Moraines and Erratic Blocks of existing Glaciers. 



There is another class of phenomena of great importance 

 in the history of existing glaciers, and of those which formerly 

 covered Switzerland. I speak of the fragments of rock of 

 every size and nature which a glacier carries along with it. 

 The appearance of the Alps seems to intimate to us that they 

 are immense ruins. Everything conspires for their destruc- 

 tion ; all the elements seem combined to abase their haughty 

 peaks. The masses of snow which rest upon them in the 

 winter, the rain which filters into their strata in summer, the 

 sudden action of the waters of torrents, and the slower, but still 

 more powerful, influence of chemical affinities, degrade, dis- 

 integrate, and decompose, the hardest rocks. Their debris fall 

 from the summits into the amphitheatres occupied by glaciers, 

 in considerable masses, accompanied by a frightful noise, and 

 large clouds of dust. Even in the middle of summer, I have 

 seen these avalanches of stones precipitated from the top of 

 the peaks of the Schreckhorn, and form on the spotless snow a 

 long black track, composed of enormous blocks, and an im- 

 mense number of smaller fragments. In spring, the rapid 

 melting of the winter's snow often gives rise to accidental 

 torrents of extreme violence. If the melting be slow, the 

 water insinuates itself into the smallest fissures of the rock, 

 becomes frozen there, and splits the most refractory masses. 



