134 AGENTS THAT DESTROY ROCKS. 



the power, especially at a high temperature, of dis- 

 solving various mineral substances. The effects of 

 this agent may be considered under four heads, viz., 

 Rains, Torrents^ Rivers, and Seas. 



The influence of rain upon rocks is not sufficient- 

 ly appreciated. Its amount, of course, will depend 

 upon the nature of the rock ; but the hardest is not 

 free from its destructive power. As it beats upon 

 the towering cliff, the rock crumbles away, and th^ 

 shattered pieces, accumulating at its base, form ex- 

 tensive beds of detritus^ which are destined to a still 

 finer division, to be eventually carried down to the 

 ocean. By the operation of rains in loosening the 

 soils on the sides of mountains, and rendering the 

 rocks slippery, land-slides often occur, carrying 

 down trees, stones, and earth to the valleys below. 

 Such slides often happen among the mountains of 

 Vermont, Massachusetts, and New-Hampshire ; and 

 one at the Notch in the White Hills, in 1826, car- 

 ried away and destroyed a whole family. This be- 

 gan near the top of the mountain, and bore down, 

 in an impetuous avalanche, the shrubs, forests, soil, 

 stones, and rocks through the space of three miles, 

 so that its desolating track is still plainly visible. 

 Mr. Lyell states that, during a tour in Spain in 

 1830, he was surprised to see " a district of gently 

 undulating ground in Catalonia, consisting of red 

 and gray sandstone, and in some parts of red marl, 

 almost entirely denuded of herbage, while the roots 

 of the pines, oaks, and some other trees were half 

 exposed, as if the soil had been washed away by a 

 flood." He however explains the appearance by 

 saying, that, being overtaken by a violent thunder- 

 storm, he saw the whole surface, even the highest 

 levels of some flat-topped hills, streaming with mud, 

 while on every declivity the devastation of torrents 

 was terrific. The effects of rain upon beds of clay 

 and sand are too w^ell known to need pointing out 

 more particularly. 



