266 ACTION OF TORRENTS. 
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. The 
simple measurement of the cubical contents of the semicircular 
hillock which he climbed before he entered the gorge, the 
structure and composition of which conclusively show that it 
must have been washed out of this latter by torrential action, 
will often account satisfactorily for the disposal of most of the 
matter which once filled the ravine. 
When a torrent escapes from the lateral confinement of its 
mountain walls and pours out of the gorge, it spreads and 
divides itself into numerous smaller streams which shoot out 
from the mouth of the ravine as from a centre, in different 
directions, like the ribs of a fan from the pivot, each carrying 
with it its quota of stones and gravel. The plain below the 
point of issue from the mountain is rapidly raised by newly- 
formed torrents, the elevation depending on the inclination of 
the bed and the form and weight of the matter transported. 
Every flood both increases the height of this central point and 
extends the entire circumference of the deposit. 
Other things being equal, the transporting power of the 
water is greatest where its flow is most rapid. This is usually 
in the direction of the axis of the ravine. The stream retain- 
ing most nearly this direction moves with the greatest momen- 
tum, and consequently transports the solid matter with which 
it is charged to the greatest distance. 
The untrayvelled reader will comprehend this the better when 
he is informed that the southern slope of the Alps generally 
rises suddenly out of the plain, with no intervening hill to 
break the abruptness of the transition, except those consisting of 
comparatively small heaps of its own débris brought down by 
ancient glaciers or recent torrents. The torrents do not wind 
down valleys gradually widening to the rivers or the sea, but 
