240 ACTION OF FORESTS ON THE FLOW OF RIVEBS. 



and maintain the violence of torrents : it is, on one hand, the friability 

 of the soil ; and, on the other, the sudden concentration of a great 

 mass of water. Now, we know already that the forests render the 

 soil less liable to be washed away ; we know also that they absorb 

 and retain a portion of the rainfall, and prevent instantaneous con- 

 centration of the portion which they do not absorb. Consequently 

 they destroy both the one and the other cause. They prolong the 

 duration of the flow, and they render the floods at once more pro- 

 longed, less sudden, and less destructive. 



" It may be understood from this how forests, in invading the 

 hasdns de reception, may have contributed powerfully to stifle certain 

 torrents. Whilst the waters were creating for themselves the most 

 convenient slopes, the forests were retaining the aoU which was ready 

 to go, were rendering it more solid, were consequently diminishing 

 the mass of earth washed away, and above all were opposing them- 

 selves to the concentration of currents. They were augmenting all 

 the resisting, all the existing obstacles, and were diminishing all the 

 motive powers ; and they were coming thus to hasten by a double 

 efficacy that epoch of stability in which the force of the waters would 

 find itself in equilibrium with the resistance of the soil. There is 

 one circumstance which ought to render their triumph stiU more 

 speedy, — it is, that the torrent, in proportion as it is enfeebled, 

 abandons to them a soil more and more stable and favourable to 

 vegetation, in such a way that this augments every day their forces 

 in proportion as the torrent loses force. In fact, if the expression 

 may be allowed, it is reinforced by the effect. 



" By this I do not mean to say that the torrents can never become 

 extinct of themselves. That would be in contradiction to what I have 

 said, and at the same time to facts observed, for there are examples 

 of torrents being extinguished without the presence of forests, and 

 solely through the erosion of the mountains — as, for instance, the 

 torrent of Saint Joseph, near Monestier. But I say that the forests 

 expedite the accomplishment of this efiect, and that they can produce 

 it where the other circumstances are not yet producing it. 



" Thus nature, in summoning forests to the mountains, places the 

 remedy side by side with the evU, She combats the active forces of 

 the waters ; to the invasions of the torrents she opposes the aggressive 

 conquests of vegetation. On those mobile revers she spreads a solid 

 layer which protects them against external attack, somewhat in the 

 manner that a facing of stone protects an earthen embankment. It 

 is worthy of remark that the little cohesion of limestones, which is 



