INFLUENCE OF THE FOREST ON SPRINGS. 229 
physical research where exact quantitative appreciation is pos- 
sible, and we must content ourselves with probabilities and 
approximations. We cannot positively affirm that the precipi- 
tation in a given locality is increased by the presence, or 
lessened by the destruction, of the forest, and from our igno- 
rance of the subterranean circulation of the waters, we cannot 
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 diminu- 
tion of the woods where they originate and through which they 
run, is as well established as any proposition in the science of 
physical geography.* 
* 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 
the 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 
ground that is cultivated, and consequently spongy and absorbent, for the 
natural soil of the prairies, has furnished a reservoir for the rains which are 
absorbed by the earth and carried gradually to the river by subterranean flow, 
instead of running off rapidly from the surface, or, as is more probable, instead 
of evaporating or being taken up by the vigorous herbaceous vegetation which 
covers the natural prairie. 
A phenomenon so contrary to common experience, as would be a permanent 
increase in the waters of a great river, will not be accepted without the most 
convintviing proofs. The present greater facility of navigation may be attrib- 
uted to improvements in the model of the boats, to the removing of sand- 
banks and other impediments to the flow of the waters, or to the confining of 
these waters in a narrower channel, by extending the embankments of the 
river, or to yet other causes. 
