50 
MOUNTAINOUS COUNTRIES-CHANGE OF CLIMATE. 
In mountainous countries, on the other hand, various 
causes combine to expose the soil to constant dangers. The 
rain and snow usually fall in greater quantity, and with much 
inequality of distribution ; the snow on the summits accumu¬ 
lates for many months in succession, and then is not unfre¬ 
quently almost wholly dissolved in a single thaw, so that the 
entire precipitation of months is in a few hours hurried down 
the flanks of the mountains, and through the ravines that 
furrow them; the natural inclination of the surface promotes 
the swiftness of the gathering currents of diluvial rain and of 
melting snow, which soon acquire an almost irresistible force, 
and power of removal and transportation ; the soil itself is 
less compact and tenacious than that of the plains, and if the 
sheltering forest has been destroyed, it is confined by few of 
the threads and ligaments by which nature had bound it 
together, and attached it to the rocky groundwork. Hence 
every considerable shower lays bare its roods of rock, and the 
torrents sent down by the thaws of spring, and by occasional 
heavy discharges of the summer and autumnal rains, are seas 
of mud and rolling stones that sometimes lay waste, and bury 
beneath them acres, and even miles, of pasture and field and 
vineyard.* 
Physical Decay of New Countries. 
I have remarked that the effects of human action on the 
forms of the earth’s surface could not always be distinguished 
from those resulting from geological causes, and there is also 
much uncertainty in respect to the precise influence of the 
* The character of geological formation is an element of very great im¬ 
portance in determining the amount of erosion produced by running water, 
and, of course, in measuring the consequences of clearing off the forests. 
The soil of the French Alps yields very readily to the force of currents, 
and the declivities of the northern Apennines are covered with earth which 
becomes itself a fluid when saturated with water. Hence the erosion of 
such surfaces is vastly greater than on many other mountains of equal 
steepness of inclination. This point is fully considered by the authors re¬ 
ferred to in chap, iii, post. 
