TT. nr. OR POISONED BY VEGETABLE GROWTH? 181 



they would not ' go witli a run,' or by the direct action 

 of rivers. Eivers would only cut ravines through 

 them ; the rest must wait for disintegration and the 

 wash of rain. The sea forms and preserves them now. 



From the universal denudation by the wash of 

 rain woods are, by comparison, free. But whether 

 the catching of aerial deposit may have anything to 

 do with it or not, or whether it is to be attributed 

 only to the protection afforded by their roots against 

 aqueous denudation, soil improves even in woods 

 which are robbed by man. 



All nature teems with carbonic acid, — earth, ocean, 

 air. All soils contain it absorbed from the atmosphere, 

 independently of rain and of that generated from or- 

 ganic remains ; and it is not only contained in all 

 superficial soils, independently of vegetable remains, 

 but it is vomited forth in vast quantities from below 

 the surface by springs of all countries, and especially 

 of all volcanic countries, as is carbonic acid gas into 

 the air by active volcanoes. Nay, beside this air 

 carriage and water carriage, there is a vast land car- 

 riage of carbonic acid from the subterranean regions. 

 In many places it exhales in a gaseous form through 

 the earth, disintegrating granite, gneiss, limestone, &c., 

 in quantities sufficient to extinguish a light or the life 

 of animals ; nay, even to destroy plants from excess of 

 this their principal food. In these forms earth dis- 

 gorges and restores what, by aqueous deposit, she may 

 be said to have previously swallowed. All water con- 



