CHAPTER IV. 



On the Effects of Forests on the Moisture over a Wide 

 ExPxVNSE OF Country. 



The observatious which we have had under consideration show 

 that forests, in common w4th other products of vegetation, withdraw 

 moisture from the ground, and that they do so to such an extent as 

 to carry off the water of swamps and to prevent the formation of 

 these increasing the atmospheric moisture in their immediate vicinity 

 to such a degree that it may be felt, making houses damp, even iu 

 their innermost chambers, and that it may be seen in clouds and fogs 

 and drizzling rain ; and yet, that they keep the soil moist compared 

 with the soil beyond their shade and shelter, wherever that shade 

 and shelter fall ; while the ground is at the same time enriched with 

 vegetable mould, the product of the fallen leaves and other dehris. 



But when we extend our study to the effects of forests on the 

 humidity of soil and climate over a wide expanse of country, we find 

 that observations have been made which seem to show that in some 

 cases the extensive destruction of forests, over a great expanse of 

 country has not perceptibly affected the quantity of the rain and 

 dew, and hail and snow, which has there fallen from heaven ; while, 

 on the other hand, there are lands which were once populous and 

 fertile, but are now arid and sterile — the aridity of which is alleged 

 to be the cause of their sterility, and to be a consequence of the 

 destruction of forests. 



On thus extending our field of observation we meet with additional 

 facts, which, if all the circumstances and conditions of each were 

 known, might be easily reconciled, notwithstanding apparently an- 

 tagonistic conclusions to which they sometimes seem to lead. 



I shall cite some of the individual or separate facts which are 

 known, illustrative of the general facts now stated ; and either as I 

 advance or subsequently, as may appear at the time most important, 

 1 shall advert to the modus operandi of the means whereby the results 

 observed may have been brought about. 



