250 
EXCAVATION BY TORRENTS. 
Tlie traveller who visits the depths of an Alpine ravine, 
observes the length and width of the gorge and the great 
height and apparent solidity of the precipitous walls which 
bound it, and calculates the mass of rock required to fill the 
vacancy, can hardly believe that the humble brooklet which 
purls at his feet has been the principal agent in accomplishing 
this tremendous erosion. Closer observation will often teach 
him, that the seemingly unbroken rock which overhangs the 
valley is full of cracks and fissures, and really in such a state 
of disintegration that every frost must bring down tons of it. 
If he compute the area of the basin which finds here its only 
discharge, he will perceive that a sudden thaw of the winter’s 
deposit of snow, or one of those terrible discharges of rain so 
common in the Alps, must send forth a deluge mighty enough 
to sweep down the largest masses of gravel and of rock.* 
which they flow. The bed of the Fersina is elevated high above the city 
of Trient, which lies near it. The Villerbacli flows at a much more 
elevated level than that of the market place of Neumarkt and Vill, and 
threatens to overwhelm both of them with its waters. The Talfer at 
Botzen is at least even with the roofs of the adjacent town, if not above 
them. The tower steeples of the villages of Schlanders, Kortsch, and 
Laas, are lower than the surface of the Gadribach. The Saldurbach at 
Schluderns menaces the far lower village with destruction, and the chief 
town, Schwaz, is in similar danger from the Lahnbach.” —Stkeffleuk, 
Ueber die Wildbache , etc., p. 7. 
* The snow drifts into the ravines and accumulates to incredible depths, 
and the water resulting from its dissolution and from the deluging rains 
which fall in spring, and sometimes in the summer, being confined by 
rocky walls on both sides, rises to a very great height, and of course 
acquires an immense velocity and transporting power in its rapid descent 
to its outlet from the mountain. In the winter of 1842-’3, the valley of 
the Doveria, along which the Simplon road passes, was filled with solid 
snowdrifts to the depth of a hundred feet above the carriage road, and the 
sledge track by which passengers and the mails were carried ran at that 
height. 
Other things being equal, the transporting power of the water is great¬ 
est where its flow is most rapid. This is usually in the direction of the 
axis of the ravine. As the current pours out of the gorge and escapes 
from the lateral confinement of its walls, it spreads and divides itself into 
numerous smaller streams, which shoot out from the mouth of the vallev. 
