52 BBSUm£ op STrKELIi'S STUDY OF 



would call a z6ne de defense, enclosed against flocks and herds. The zones 

 of the two banks, following the outline of the basin, would meet in the heights, 

 and would begird the torrent like a girdle. The breadth, Tarying with the 

 slope and with the consistency of the soil, would be about 40 metres, or 130 

 feet, below, but it would increase rapidly as the zone rose on the mountain 

 side', and it would end in embracing a space of 400 or 500 metres, or from a 

 quarter to a third of a mile. 



" This outline would require to follow, not only the principal branch of the 

 torrent, but also the different secondary torrents which degorge into the first ; 

 following then the ravines which each of the secondary torrents receives, and 

 going on thus, from branch to branch, it would go on to the birthplace of 

 the last threadlet of water. In this way the torrent would find itself begirt 

 thoughout the most minute of its ramifications. These zones of defence, in 

 penetrating the hassin de reception, will be enlarged ; while, on the other 

 hand, as the ramifications are in this part more multiplied and more approxi- 

 mated, it will come to pass that neighbouring zones will join and even over- 

 lap each other, and their outlines will be lost in a common region, which will 

 cover the whole of this part of the mountain, without leaving there a void 

 space. The zones of enclosure being thus determined, the first part of the 

 operation is finished. But this is in some respects only the outline of the 

 periphery of the work which is to be done. 



" We have next to do with what may be the most active and prompt 

 means of drawing vcpcetation over the whole surface of this enclosure. For 

 this purpose it should -be sown and planted with trees ; where it may be 

 impossible to raise trees at once, the growth of shrubs, bushes, and thorns 

 should be stimulated ; but on the height, where the zones include the whole 

 extent of the hassin de riceiJtion, it is a forest which must be created. The 

 best adapted kind of trees must be selected ; recourse must be had to all 

 modes of procedure, indeed, even to modes of procedure which have yet to 

 be discovered, and which go beyond experience. The work must be done 

 any way and every way ; and the end aimed at in these works ought to be to 

 cover the hassin de reception by a forest which will every day become more 

 dense, and which, extending itself step by step, will end in spreading even 

 into the most hidden depths of the mountain, i 



" If the vegetation thus developed over the zones of defence be protected 

 against flocks, if it be protected against the depredations of the inhabitants, 

 if it be tended, maintained, stimulated by all means possible, it will ulti- 

 mately envelope all the parts of the torrent by a very dense thicket, and 

 thereby will be realized two efiects at once, both of them equally salutary. 



" First, this will arrest the waters which trickle down the svirface of the 

 soil, and will keep them from entering the torrent ; or, if it do not prevent 

 them doing this, it will at least retard them, and we know that this result 

 is in every way a happy one. From the time this is done the torrent will 

 only receive the waters which fall vertically from the sky into its bed ; and 

 this will diminish its volume in the same proportion as the proportion which 

 exists between the extent of the general basin of the mountains and that of 

 the stringently reduced opening presented by this bed. From a considera- 

 tion of the great diff'erence in extent of these two surfaces may be under- 

 stood how great should be the reduction of the body of waters thus effected. 

 And next, the ground of these zones can be no more washed away by the 

 rains, and swept away by the torrent, and thereby will bo diminished so far 

 the mass of deposited matter. It is true, it may indeed be swallowed up little 



