250 DEVASTATIONS OCOASlONED BY TOBRBNTS, 



three mountains ; and some of the affluents are 20 and 30 kilomfetres, or 14 

 and 20 miles, in length. In aU the upper parts of these, which may be 

 considered the sources of the torrent, the ground is comparatively firm, 

 and the water limpid; but when it approaches the gullet by which it 

 debouches into the plain, it traverses an extensive bed of detritus, 

 apparently a formation of the glacial period, an old morraine it may be, a 

 confused mixture of mud, and sand, and erratic blocks, torn from the far off 

 summits of the High Alps. In this quarter the torrent is enclosed in pre- 

 cipitous banks, to the depth of 100 metres, or nearly 350 feel, and these 

 banks are being eaten away unceasingly at their base, and are in a state of 

 the most complete instability. 



" Here the torrent at once changes its character ; clear thus far, here it 

 loads itself with muddy dejections — the everchanging divarications begin — 

 and the least storm of rain causes the hills to crumble down, and gives rise 

 to the most violent effects of a debdcle, or breaking up of a dam. Near to 

 this spot the principal torrent receives two considerable affluents : on the 

 right, the torrent of the Grande Combe comes down from the mountain 

 Saint-Sauvier ; while, on the left, the torrent de I'Homme tears and eats 

 away, in a great fan-shaped basin, the mountain of Baratier, These two 

 torrents wear down a black schistose earth of the worst kind, aud, between 

 the two, a single flood suffices partially to dam up the principal torrent, 

 which is then driven against one or other of the confining unstable banks. 

 Thus all the producing causes of disaster meet within a space of about a 

 kilomtoe, or two-thirds of a mile square j for this reason those desolate 

 spots have been chosen by M. Costa as the field of battle, while he is 

 satisfied with simply prohibiting the access to flocks in the upper part of 

 the basin. 



"The bold plan, which is in course of execution, consists in breaking the 

 living force of the principal torrents by a massive wall, behind which the 

 ■water-course will accumulate its dejection in such a way that the base of the 

 existing banks forming the gullet will be covered deep by these ; the crest 

 of these banks will then be broken down, and a gentle and regular slope 

 will replace the torn and ruinous surfaces which they now present. WhUe 

 these works are in course of execution, a longitudinal dike, built higher up 

 the barrages, in a situation happily chosen, prepares for the torrent an arti- 

 ficial bed, into which it will be cast when they shall have banked up the 

 ancient bed. 



" One of the two affluents mentioned above, de I'Homme, already 

 extinguished by planted banks and small barrages, has become innocuous. 

 And its counterpart, coming in an opposite direction, the torrent of the 

 Grande Combe, which now, after having flowed for some distance parallel 

 to the principal torrent, falls into this below the wear, will, by means of a 

 cutting, the locality for which is indicated by a natural depression in the 

 ground, be brought into the torrent above that barrage. And by the 

 change thus made the torrent of the Grande Combe will be led away to a 

 distance from the black schist, with which it "now charges itself to 

 repletion ; the bed which is now hollowing out will be filled, and the hills 

 between which it now flows will be laid out in banks and subjected to the 

 usual treatment. 



" M. Costa hopes, that by the new channel which he has in view for the 

 torrent of the Grand Combe, the extinction of it will be brought about as 

 bj stage effect, for in the course of a few hours the muddy waters of to-day 



