220 INFLUENCE OF THE FOREST ON SPRINGS. 
able stratum, and then be conducted along it, until, finally, at the 
outcropping of this stratum, it bursts from a hillside as a run- 
ning spring. But such instances 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 sup- 
posed is covered by a layer of vegetable earth thick enough to 
retain, until it is evaporated, all the rain that falls upon it, with- 
out 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 argu- 
ment, the observations of Boussingault are, both in the circum- 
stances 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 Boussin- 
gault’s own words, the facts and some of the remarks with which 
he accompanies the detail of them. “ In many localities,” 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 utilized as a motive-power ; at other points, 
there are grounds for believing that rivers have become shal- 
lower, 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 obser- 
vations have been principally made in valleys bounded by high 
mountains, and it has been noticed that this diminution of the 
waters has immediately followed the epoch when the inhabitants 
have begun to destroy, unsparingly, the woods which were 
spread over the face of the land. 
“ And here lies 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 Ara- 
gua, having no outlet to the ocean, form, by their union, the 
Lake of Tacarigua or Valencia, having a length of about two 
leagues and a half [= 7 English miles]. 
* Economie Rurale, t. ii., p. 730. 
