CRUSHING FORCE OF TORRENTS. o71 
of such causes to replace, by a new creation, the Iden he has 
wasted. 
Crushing Force of Torrents. 
I must here notice a mechanical effect of the rapid flow of 
the torrent, which is of much importance in relation to the des- 
olating action it exercises by covering large tracts of cultivated 
ground with infertile material. The torrent, as we have seen, 
shoots or rolls forwards, with great velocity, masses and frag- 
ments of rock, and sometimes rounded pebbles from more an- 
cient formations. Every inch of this violent movement is 
accompanied with crushing concussion, or, at least, with great 
abrasion of the mineral material, and, as you follow it along 
the course of the waters which transport it, you find the stones 
gradually rounding off in form, and diminishing in size, until 
they pass successively into grayel, and, in the beds of the rivers 
to which the torrents convey it, sand, and lastly impalpable 
slime. 
There are few operations of nature where the effect seems 
more disproportioned to the cause than in this crushing and 
comminution of rock in the channel of swift waters. Igneous 
rocks are generally so hard as to be wrought with great dif_i- 
culty, and they bear the weight of enormous superstructures 
without yielding to the pressure; but to the torrent they are 
as wheat to the millstone. The streams which pour down the 
southern scarp of the Mediterranean Alps along the Riviera di 
Ponente, near Genoa, have short courses, and a brisk walk of a 
couple of hours or even less takes you from the sea-beach to 
the headspring of many of them. In their heaviest floods, they 
bring rounded masses of serpentine quite down to the sea, but 
at ordinary high water their lower course is charged only with 
finely divided particles of that rock. Hence, while, near their 
sources, their channels are filled with pebbles and angular frag- 
ments, intermixed with a little gravel, the proportions are re- 
versed near their mouths, and, just above the points where 
their outlets are partially choked by the rolling shingle of the 
