82 EFFECT OF FOEFSTS ON MARSHES. 



advanced ; and that this was the case I have no doubt. But along 

 ■frith this there may have been combined another operation, mora 

 simple, mechanical, and intelligible, which must not be overlooked. 



I have never heard particulars of a case which seemed to run 

 counter to the exposition which I have given, of which I have not 

 been able to show that it was compatible, or consistent, with the 

 supposition that the operation was such as I have supposed. But 

 there is another operation, noticed by Becquerel, to which Marsh 

 considers that sufficient importance has not, until very recently, been 

 generally ascribed, namely, the mechanical action of roots as con- 

 ductors of the superfluous humidity of the superficial earth to lower 

 strata. " The roots of trees," says he, " often penetrate through 

 sub-soil almost impervious to water, and in such cases the moisture, 

 which would otherwise remain above the sub-soil, and convert the 

 surface earth into a bog, follows the root downwards and escapes 

 into more porous strata, or is received by subterranean canals or 

 reservoirs. When the forest is felled, the roots perish and decay, the 

 orifices opened by them are soon obstructed, and the water, after 

 having saturated the vegetable earth, stagnates on the surface and 

 transforms it into ponds and morasses. Thus, in La Brenne, a tract 

 of 200,000 acres resting on an impermeable sub-soil of argillaceous 

 earth, which ten centuries ago was covered with forests, interspersed 

 with fertile and salubrious meadows, has been converted by the 

 destruction of the woods into a vast expanse of pestilential pools and 

 marshes. In Sologne the same cause has withdrawn from cultivatiou 

 and human habitation not less than 1,100,000 acres of ground, once 

 well-wooded, well-drained, and productive." 



It is with the fact that such results have followed such proceedings 

 that we have to do. From the facts alone we may learn wisdom, 

 though we should be baffled in attempting to trace the process by 

 which the results have been produced, and explanations ofiered by 

 others may appear to us unsatisfactory. 



We have learned that food invigorates us and sleep refreshes, 

 and we act upon the knowledge of the facts, though we may be 

 unable to explain how it is that these results are produced. And 

 we find that thus the knowledge of these facts has been utilised in 

 Eussia, where a morass appearing on the destruction of a forest is 

 replanted with willows. Pines and firs grew there before ; but 

 pines and firs would not grow now, and thus is brought before us 

 another view of the subject: not only has the destruction of 



