134 AGENTS THAT DESTROY ROCES. 
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 the 
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 ia 
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 well known to need pointing out 
more particularly. 
