INFLUENCE OF THE FOEEST ON SPRINGS. 225 



Uon of flood-water during rains — ^increase of delivery at other 

 seasons." 



Becquerel and other European writers adduce numerous other 

 cases where the destruction of forests has caused the disappear- 

 ance of springs, a diminution in the volume of rivers, and a 

 lowering of the level of lakes; in fact, the evidence in sup- 

 port of the doctrine I have been maintaining on this subject 

 seems to be as conclusive as the nature of the case admits.* We 

 can not, it is true, arrive at the same certainty and precision of 

 result in these inquiries as in those branches of physical research 

 where exact quantitative appreciation is possible, and we must 

 content ourselves with probabilities and approximations. "We can 

 not positively affirm that the precipitation in a given locahty is 

 increased by the presence, or lessened by the destruction, of the 

 forest, and from our ignorance of the subterranean circulation of 

 the waters, we can not predict, with certainty, the drying up of a 

 particular spring as a consequence of the felling of the wood 

 which shelters it ; but the general truth, that the flow of springs 

 and the normal volume of rivers rise and fall with the extension 

 and the diminution of the woods where they originate and through 

 which they run, is as well established as any proposition in the 

 science of physical geography, f 



* See, in the Bevue des Eaux et Forits for April, 1867, an article entitled 

 De I'influence des Farets sur le Regime des Faux, and the papers in previous 

 numbers of the same journal therein referred to. 



f Some years ago it was popularly believed that the volume of the Missis- 

 sippi, like that of the Volga and other rivers of the Eastern Hemisphere, was 

 diminished by the increased evaporation from its basin and the drying up of 

 springs, in consequence of the felling of the forests in the vicinity of the 

 sources of its eastern affluents. The boatmen of this great river and other 

 intelligent observers now assure us, however, that the mean and normal level 

 of the Mississippi has risen within a few years, and that in consequence the 

 river is navigable at low water for boats of greater draught, and at higher 

 points in its course, than was the case twenty-five years ago. 



This supposed increase of volume has been attributed by some to the recent 

 re-wooding of the prairies, but the plantations thus far made are not yet 

 sufficiently extensive to produce an appreciable effect of this nature ; and 

 besides, while young trees have covered some of the prairies, the destruction 

 of the forest has been continued perhaps in a greater proportion in other parts 

 of the basin of the river. A more plausible opinion is that the substitution of 

 groimd that is cultivated, and consequently spongy and absorbent, for the 

 10* 



