266 
MOUNTAIN SLIDES. 
The soil that protects the lime and sand stone, the slate and 
the granite from the influence of the sun, also prevents the 
water which filters into their crevices and between their strata 
from freezing in. the hardest winters, and the moisture de¬ 
scends, in a liquid form, until it escapes in springs, or passes 
off by deep subterranean channels. But when the ridges are 
laid bare, the water of the autumnal rains fills the minutest 
pores and veins and fissures and lines of separation of the 
rocks, then suddenly freezes, and bursts asunder huge, and 
apparently solid blocks of adamantine stone.* Where the 
strata are inclined at a considerable angle, the freezing of a 
thin film of water over a large interstratal area might occasion 
a slide that should cover miles with its ruins; and similar 
results might be produced by the simple hydrostatic pressure 
of a column of water, admitted by the removal of the covering 
of earth to flow into a crevice faster than it could escape 
through orifices below. 
Earth or rather mountain slides, compared to which the 
catastrophe that buried the Willey family in New Hampshire 
was but a pinch of dust, have often occurred in the Swiss, 
Italian, and French Alps. The land slip, which overwhelmed, 
* Palissy had observed the action of frost in disintegrating rock, and he 
thus describes it, in his essay on the formation of ice: “I know that the 
stones of the mountains of Ardennes be harder than marble. Neverthe¬ 
less, the people of that country do not quarry the said stones in winter, for 
that they be subject to frost; and many times the rocks have been seen to 
fall without being cut, by means whereof many people have been killed, 
when the said rocks were thawing.” Palissy was ignorant of the expan¬ 
sion of water in freezing—in fact he supposed that the mechanical force 
exerted by freezing water was due to compression, not dilatation—and 
therefore he ascribes to thawing alone effects resulting not less from con¬ 
gelation. 
Various forces combine to produce the stone avalanches of the higher 
Alps, the fall of which is one of the greatest dangers incurred by the ad¬ 
venturous explorers of those regions—the direct action of the sun upon 
the stone, the expansion of freezing water, and the loosening of masses 
of rock by the thawing of the ice which supported them or held them 
together. 
