INFLUENCE OF THE FOREST ON SPRINGS. 217 



more bibulous, and at the same time less retentive, than its orig- 

 inal covering. Under such circumstances, the water of precipita- 

 tion, which had formerly been absorbed by the vegetable mould 

 and retained until it was evaporated, might descend through por- 

 ous earth until it meets an impermeable stratum, and then be 

 conducted along it, until, finally, at the outcropping of this stra- 

 tum, it bursts from a hiUside as a running spring. But such in- 

 stances are doubtless too rare to form a frequent or an important 

 exception to the general law, because it is very seldom the case 

 that such a soil as has just been supposed is covered by a layer of 

 vegetable earth, thick enough to retain, until it is evaporated, all 

 the rain that falls upon it, without imparting any water to the 

 strata below it. 



If we look at the point under discussion as purely a question of 

 fact, to be determined by positive evidence and not by argument, 

 the observations of Boussingault are, both in the circumstances 

 they detail and in the weight to be attached to the testimony, 

 among the most important yet recorded. The interest of the 

 question will justify me in giving, nearly in Boussingault's own 

 words, the facts and some of the remarks with which he accom- 

 panies the detail of them. " In many locahties," he observes,* 

 " it has been thought that, within a certain number of years, a 

 sensible diminution has been perceived in the volume of water of 

 streams utihzed as a motive-power ; at other points, there are 

 grounds for believing that rivers have become shallower, and the 

 increasing breadth of the belt of pebbles along their banks seems 

 to prove the loss of a part of their water ; and, finally, abundant 

 springs have almost dried up. These observations have been 

 principally made in valleys bounded by high mountains, and it 

 has been noticed that this diminution of the waters has imme- 

 diately followed the epoch when the inhabitants have begun to 

 destroy, unsparingly, the woods which were spread over the face 

 of the land. 



" And here hes the practical point of the question ; for if it is 

 once established that clearing diminishes the volume of streams, 

 it is less important to know to what special cause this effect is 

 due. The rivers which rise within the valley of Aragua, having 



* J^conomie Rurale, t. ii., p. 730. 

 10 



