184 



SOILS AIs-D VEGETABLE GROWTH. 



TT. III. 



denudation. In the case which Lyoll mentions, of 

 bogs formed ' by the fall of trees and the stagna- 

 tion of water caused by their trunks and branches 

 obstructing the free drainage of the atmospheric 

 waters, and giving rise to a marsh,' and ' of mosses 

 where the trees are all broken within two or three 

 feet of the original surface, and where their trunks all 

 lie in the same direction,' it is not the trees which are 

 dying out on soils that have ' become exhausted for 

 trees ' which break or blow over in wind : but, on the 

 contrary, the trees which break or blow over in wind 

 are the rank product of a soil which suits them, and 

 which grows them too close to have side-boughs, and 

 consequently too tall for their girthing and for their 

 circumscribed roots. Many countries have ceased to 

 be covered with forests from many different causes ; 

 but the last cause I should assig;n would be the soil 

 becoming exhausted for trees. The formation of bogs 

 by the over-huntriance of woods may be one of these 

 causes. I think it possible that, in some cases, tlie 

 irruption of peat into woods from the bursting of bogs 

 above them may have violently overtlirown the trees ; 

 in this case the trees should all lie down the stream ; 

 or that the drift from above, and quiet deposit of 

 alluvial peat into woods, by suffocating the roots, may 

 have killed the trees and caused their fall, instead of 

 the fall of the trees causing the bog ; but in this case 

 it is unlikely that the stems should lie all one way, yet 

 this is possible if the tract is only exposed to wind on 

 one side. 



