MOUNTAIN SLIDES. 277 



Moimtam Slides. 



Terrible as are the ravages of the torrent and the river-flood, 

 the destruction of the woods exposes human hfe and industry to 

 calamities even more appalling than those which I have yet de- 

 scribed. The shde in the JS'otch of the White Mountains, by 

 which the "Willey family lost their hves, is an instance of the sort 

 I refer to, though I am not able to say that in this particular case 

 the shp of the earth and rock was produced by the denudation of 

 the surface. It may have been occasioned by this cause, or by 

 the construction of the road through the IS'otch, the excavations 

 for which perhaps cut through the natural buttresses that sup- 

 ported the sloping strata above. 



ITot to speak of the fall of earth when the roots which held it 

 together, and the bed of leaves and mould which sheltered it 

 both from disintegrating frost and from sudden drenching and 

 dissolution by heavy showers, are gone, it is easy to see that, in a 

 climate with severe winters, the removal of the forest, and con- 

 sequently of the soil it had contributed to form, might cause the 

 displacement and descent of great masses of rock. The woods, 

 the vegetable mould, and the soil beneath, protect the rocks they 

 cover from the direct action of heat and cold and from the ex- 

 pansion and contraction which accompany them. Most rocks, 

 while covered with earth, contain a considerable quantity of 

 water.* A fragment of rock pervaded with moisture cracks and 



imposture ; and those founded, not on direct estimation by competent observ- 

 ers, but on the report of persons who have no particular interest in knowing 

 the truth, are often a motive for distorting it, are commonly to be regarded as 

 but vague guesses at the actual fact. 



* Eock is permeable by water to a greater extent than is generally supposed. 

 Marble, and even granite, as well as most other stones, when freshly quarried, are 

 sensibly heavier, as well as softer and more easily wrought, than after they 

 are dried and hardened by air-seasoning. Many sandstones are porous enough 

 to serve as filters for liquids, and much of that of Upper Egypt and Nubia 

 hisses audibly when thrown into water, from the escape of the air forced out 

 of it by hydrostatic pressure and the capillary attraction of the pores for 

 water. The purest water near London is that derived from precipitation 

 and stored up by nature in the dense chalk formations of the interior of the 

 country. 



Even the denser silicious stones are penetrable by fluids and the coloring 

 matter they contain, to such an extent that agates and other forms of silex 



