PT. nr. OR POISONED BY VEGETABLE GROWTH? 183 



powdered rock. So that vegetation may be said to 

 produce vegetation ; and we may possibly see in this 

 general tendency to the increase of vegetable remains 

 a main cause of the formation of bogs : and perhaps 

 aqueous denudation may be a necessary agent to pre- 

 vent the undue increase of vegetable remains over the 

 whole surface of the earth. 



And natural forests return to the soil all they take No neces- 



sitj' for 



from it, and with interest : and Lyell should not talk rotation in 



nature s 



of trees dying out from the soil having ' become ex- cropping, 

 hausted for trees,' or of the necessity of rotation in 

 nature's cropping. Eotation of crops is only necessary 

 w^here man robs the soil of the produce he has raised, 

 or raises plants by cultivation such as nature could not 

 raise without cultivation. Plants in a state of nature 

 stick to their appropriate stations^ so long as the 

 physical conditions of those stations remain unaltered. 

 The doctrine of rotation is in direct contradiction to 

 the doctrine of fixed stations for plants. 



It is perhaps prohahle that were wheat sown every 

 year on the same land, and ploughed in before ripen- 

 ing, the land would be enriched, not impoverished ; 

 that is, a great increase of carbonic acid would prob- 

 ably occur from vegetable chemistry, and a great 

 increase of the inorganic constituents of plants from 

 disintegration. In fact, although bearing wheat every 

 year, the soil would become as rich as maiden soils 

 always are. A process resembling this is wdrat does go 

 on in natural forests, in addition to the absence of 



