126 EFFECTS OF WATER. 



quantity than at other times, in consequence of its low temperature ; 

 and running over calcareous masses, it forms furrows which gra- 

 dually deepen, and sometimes cause very considerable falls of rock. 

 These slow effects of water are particularly remarked in the Alps 

 and Pyrenees, where the snows remain a part of the year, and 

 melt by degrees in the fine season. 



7. Softening power. Water, by penetrating argilla'ceous beds, 

 sometimes softens them so much, that they cannot remain on the 

 slopes they occupied, and fall from their own weight; this is the 

 cause of many falls or slides in sedimentary formations. One of 

 ihe most remarkable catastrophes of this kind happened in 1806 

 at Ruffiberg or Rossberg in Switzerland, after a very rainy sea- 

 son. The argillaceous matters which cemented the rolled flints 

 forming the mountain becoming softened, a mass of more than 

 50,000,000 of cubic yards was suddenly detached, and precipitated 

 into the valley, forming in it hills sixty yards high, and burying 

 several villages under masses of mud and flints. We often see, 

 on a small scale, thick beds of rock gently slide to the bottom of 

 valleys, on softened argilla'ceous beds which supported them, and 

 tranquilly displace plantations and even the inhabitants on them, 

 without the proprietors perceiving it at the first moment. 



8. Waters which filter through rocks to argilla'ceous layers 

 which may arrest them, and on the plane of which they are 

 directed to the surface, sometimes soften these substances also, 

 carrying away parts successively, and especially sands that may 

 rest on them, laying bare in this way underlying beds: this is 

 termed denudation. There results from this, at the point where 

 the w r ater breaks forth from the declivity of hills, more or less ex- 

 tensive voids, which leave the solid superposed masses without 

 support, which are then dislocated in different ways (fig. 209) and 



- 209. Fig. 210 



Escarpments produced by the action of water. 



*oon overthrown. This is frequently seen in certain escarpments, 

 Dt the base of which are found argilo-arena'ceous layers which con- 

 iuct tne springs externally. 



7. What are the effects of the softening power of water on rocks ? 



8. What is meant by denudation ? 



