182 ARE SOILS EMICHED, IMPOVERISHED, n. nr. 



tains it, fresh or salt, well, spring, or rain. Add to 

 this the constant enormous supply generated chemi- 

 cally 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 vegetable 

 chemistry on sap absorbed by the roots. 



Suppose we take a mass of volcanic rock, in which 

 there can be no vegetable or organic remains wliat- 

 ever, 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 equivalent 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 ammonia 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 decay- 

 ins^ will so increase the stock of carbonic acid, that 

 more plants will hereafter grow. Now, to prevent 

 the effect of my aerial denudation, let us bury the 

 heads as well as tlie roots of these plants below the 

 soil. Every such plant, large or small, will, in decay, 

 become a hoard of carbonic acid fixed in the soil for 

 the food of future plants, in addition to the annual 

 supply of carbonic acid and ammonia to the soil from 

 the air and from rain. The carbonic acid of decaying 

 vegetation will also help the rain in disintegrating our 



