48 nisuMi OF buhell's study op 



■within a little of being ruined. The same observation has also been made 

 on the Lower Alps. We may cite as an example of what has been said 

 the whole of the revers which are situated on the left' bank of the 

 Durance, from Sabines to the river Ubaye. It is formed exclusively by a 

 succession of beds of dejection belonging to ancient torrents, which had 

 been extinguished after having gnawed away a great portion of the mountain 

 of Morgon. The whole of this district was covered with forests, which have 

 been cut up with clearings, and which continue to be impoverished still 

 further every day. The torrents also have coinmenced their devastations, 

 and, if the destruction of woods be continued with the same recklessness, 

 this revers, fertile to-day, will speedily be ruined, as so many others have 

 been. 



" This last fact completes all that need be said in regard to the influence 

 of forests. In seeing these show themselves almost everywhere on the body 

 of extinct torrents, one may suppose that these had first died, and that the 

 woods had then seized upon them when the extinction had been completed, 

 and when the soil of the neighbourhood, become stable, permitted vegetation 

 to develope itself in safety : the forest would then only have been one of the 

 efiects of the extinction of these, instead of being the cause of it. But then 

 the destruction of the woods would only have restored things to their pri- 

 mitive state, and the torrent ought to have been able to continue extinct 

 after the taking away of the woods as it was before their appearance there 

 — and this is exactly what does not happen. It has sufficed to clear away 

 the woods to see the devastations immediately reappear. It must be then 

 the forests which, by their permanent appearance on the soil, hindered the 

 devastations, and it is the forests, in taking possession of the soil, which 

 have again caused them to cease — and the extinction of the torrents is so 

 completely their work that it begins, continues, and disappears with them, 

 the effect ceasing immediately with the cause. 



" One sees by this that the action of forests is not confined to preventing 

 the creation of new torrents, but that it is sufficiently energetic to destroy 

 torrents already formed. One sees also that the injurious result of the 

 removal of woods is not only to open everywhere the soil to new torrents, 

 but that it augments the violence of those which exist, and resuscitates 

 those which appear completely extinct. We may then sum up the influence 

 which forests exercise on torrents already formed in two facts, parallel to 

 those which sum up tbeir influence on lands where the torrents have not 

 yet appeared. (1.) The presence of a forest on a soil prevents the formation 

 of a torrent there. (2.) The destruction of forests leaves them subject to 

 become the prey of torrents. Nor is there in this any thing for which we 

 may find it difficult to account. 



" When the trees fix themselves in the soil the roots consolidate this, inter- 

 lacing it with a thousand fibres ; their branches protect it, as would a buckler 

 against the shock of the heavy rains ; and their trunks, and at the same 

 time the suckers, brambles, and that multitude of shrubs of all kinds which 

 grow at their base, oppose additional obstacles to the currents which would 

 tend to wash it away .^. The effects of all this vegetation is thus to cover the 

 soil, in its nature mobile, with an envelope more solid and less liable to be 

 washed away. -^ Besides, it divides the currents and disperses them over the 

 whole surface of the p,round,)which keeps them from going ofi' in a body in 

 the lines of the thalweg and meeting there, which would be the case if they 

 flowed freely over the smooth surface of a denuded ground. Finally, it 



