r 21 3 



Under common circumstances the lime from the mag- 

 nesian limestone is, however, used in moderate quan- 

 tities upon fertile soils in Leicestershire, Derbyshire, 

 and Yorkshire, with good effect ; and it may be ap- 

 plied in greater quantities to soils containing very large 

 proportions of vegetable matter. Magnesia when 

 combined with carbonic acid gas, seems not to be pre- 

 judicial to vegetation, and in soils rich in manure, it 

 is speedily supplied with this principle from the de- 

 composition of the manure. 



After the nature and operation of manures have 

 been discussed, the next, and the last subject for our 

 consideration, will be some of the operations of hus- 

 bandry capable of elucidation by chemical principles. 



The chemical theory of fallowing is very simple. 

 Fallowing affords no new source of riches to the soil. 

 It merely tends to produce an accumulation of decom 

 posing matter, which in the common course of crops 

 would be employed as it is formed, and it is scarcely 

 possible to imagine a single instance of a cultivated 

 soil, which can be supposed to remain fallow for a 

 year with advantage to the farmer. The only cases 

 where this practice is beneficial seems to be in the des- 

 truction of weeds, and for cleansing foul soils. 



The chemical theory of paring and burning, I 

 shall discuss fully in this part of the Course. 



It is obvious that in all cases it must destroy a 

 certain quantity of vegetable matter, and must be 

 principally useful in cases in which there is an excess 

 of this matter in soils. Burning, likewise renders 

 clays less coherent, and in this way greatly improves 



