Part III.] OR POISONED BY VEGETABLE GROWTH? 
205 
a run/’ or by the direct action of rivers. Rivers 
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 im¬ 
proves 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 organic remains; and it is 
not only contained in all superficial soils, inde¬ 
pendently 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 carriage of carbonic acid from the subter¬ 
ranean regions. In many places it exhales in a 
gaseous form through the earth, disintegrating 
granite, gneiss, limestone, &c. in quantities suf¬ 
ficient to extinguish a light or the life of ani- 
