Effects of Frost and Oxidation on Rocks. 5 



clear springs, and forms a beautiful mountain stream, called the 

 Oschenen-bach. 



On comparing those cases of landslips in the Alps, which are 

 attested by living witnesses, or by written records, with similar 

 appearances, such as those now described, respecting which his- 

 tory is silent, we are enabled to draw the conclusion, that land- 

 slips have occurred very frequently in the stratified mountains. 



2. But, notwithstanding the frequency of landslips in the Alps, 

 and their very striking and terrific appearances, their supply of 

 materials for alluvial action is inconsiderable, compared with the 

 quantity furnished by those agents, such as frost and oxidation, 

 which separate rocks more gradually and more constantly. 



No clearer examples of the agency of frost in disintegration 

 can be found than in the large masses which fall upon the sea- 

 shore from our own chalk-cliffs in the course of every winter. 

 Upon all rocks, in every situation, freezing water acts in a simi- 

 lar way. But in mountains of sufficient elevation, water freezes 

 only in the summer ; and then, by melting and freezing every 

 successive day and night, it must exert a proportionably greater 

 effect in loosening the rocks, into the exposed parts of which it 

 has penetrated. Tlie more frequent freezing of water in a gx-eat 

 elevation is the necessary consequence of the nearer approach of 

 the ordinary temperature of the place to the freezing point, and 

 its effect is seen upon the glaciers, where, during summer, innu- 

 merable small pools are, in the morning, covered with a pellicle 

 of ice, and in the middle of the day converted into flowing rills. 

 We only need reflect on the corresponding daily change in the 

 surfaces of the rocks, by which these glaciers are surrounded, in 

 order to be satisfied that the effect of frost must be greater in 

 cold t|ian in temperate regions. 



The older rocks disintegrate more or less rapidly, in propor- 

 tion as they are more or less prone to oxidation. Hence we 

 sometimes find granite and other primitive rocks hard, smooth, 

 and tough, to the very moment when they fall ; and, at other 

 times, the slightest blow of the hammer separates them into 

 flakes, or with the hand alone we may reduce them to coarse 

 sand. In all their various degrees of comminution, we find these* 

 rocks upon the summits of the Alps as well as in lower situa- 

 tions, and hence we see different glaciers either eml>rowned with 



