206 
ARE SOILS ENRICHED, IMPOVERISHED, [Part III. 
mals; nay, even to destroy plants from excess 
of this their principal food. In these forms earth 
disgorges and restores what, by aqueous deposit, 
she may be said to have previously swallowed. 
All water contains it, fresh or salt, well, spring, 
or rain. Add to this the constant enormous 
supply generated chemically in the decay of 
animal and vegetable substances, and we have 
quite enough to account for the increase of 
vegetable matter formed by the action of vege¬ 
table chemistry on sap absorbed by the roots. 
Suppose we take a mass of volcanic rock, in 
which there can be no vegetable or organic re¬ 
mains whatever, that we grind this into powder, 
and expose it to the air in an open case a foot in 
depth, whose lower part is sieve-like and equiva¬ 
lent to a porous subsoil. The powdered rock 
will be disintegrated by the action of the air and 
rain. It will also absorb carbonic acid and am¬ 
monia from the air and rain. An infinite variety 
of seeds will be brought to this soil by my pet 
aerial deposit. Very few at first will grow, on 
account of the small store of carbonic acid in 
the soil. But if they do not grow, or if they 
only partially grow, they will decay; and in 
decaying will so increase the stock of carbonic 
acid, that more plants will hereafter grow. 
