220 ACTION OF FORESTS ON THE SURFACE-FLOW OF RAIN WATER. 



that there is impermeable rock underlying the humus : all the water 

 should arrive at this bed of rock and flow down, but the hydroscopicity 

 and capillarity of this humus — of the ground — of the foliage — of the 

 branches of the trees — in a word, of the material of which the forest 

 is composeil — will arrest the water to such a degree and measure as 

 to regulate temporarily the delivery. . . 



" I have glanced rapidly at the action of forests, in view simply of 

 their effect on the water which falls on their surface ; but tlieir 

 function is by no means limited to this, for they serve also to arrest 

 the waters which come from the pastures above them. They constitute 

 in some measure a kind of immense and powerful barrage, or barrier 

 placed between the summit and the bed of the valleys. 



" In support of this allegation, I shall cite personal observations 

 which seem to me conclusive. Never have I seen, during the most 

 violent storms of rain, superficial flowings of water in the forests 

 situated under pastures, though such flowings may have existed in the 

 meadows at a greater elevation than the forests ; all the waters which 

 these supplied were literally absorbed aad retained by the forest soil. 

 I except, intent. onally, well-m irked ravines, which coming from above 

 traverse forests, for the question here is only of slopes somewhat uniform, 

 or but slightly undulated ; it is evident that the soil of the forest will 

 not absorb the water of a stream which traverses it encased in a bed. 

 " I take, for example, a valley which rises to a summit line some- 

 what elevated. The end situated at a great height is formed entirely 

 of pasture lands, which spread out equally on the summits of the 

 brows of the mountains ; at a lower level beneath these are the 

 forests. The waters which fall into the cistern formed by the head 

 of the valley rapidly accumulate, and give birth to a torrent which 

 traverses the forest. On the contrary, that which falls on the pasture 

 lands above the brows do not commonly readh the depth of the 

 ravine ; descending to the forest zone uniformly extended over the 

 soil, they are there absorbed. 



" In a word, the zone of the forest absorbs generally the water 

 flowing from the zone of pasture lands which correspond to it. In 

 support of these observations, I appeal to all who, in the Alps, have 

 observed storms of rain in the forest. I except water accumulated in 

 ravines or depressions, which are in another condition. 



" But the beneficent action of the forests does not limit itself to 

 this ; the flow in the ravine may also, if it be not completely absorbed, 

 be by them rendered less injurious if it should come to spread itself 

 over a cone de ddjection in a forest otherwise covered with wood. I 



