Fallowing affords a source of riches to the soil, 
in consequence of the absorption of oxygene and 
the aqueous principles of the atmosphere, and so 
tends to produce an accumulation of decomposing 
matter, which, in the common course of crops, 
would be employed as it is formed, yet in highly 
cultivated soils, under a regular succession of crops 
properly manured, this practice can rarely be 
advantageous : and the cases in which it is really 
beneficial are for the destruction 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 their texture, and causes them to be less 
permeable to water. 
The instances in which it must be obviously 
prejudicial, are those of sandy dry siliceous soils, 
containing little animal or vegetable matter. Here 
it can only be destructive, for it decomposes that 
on which the soil depends for its productiveness. 
The advantages of irrigation, though so lately a 
subject of much attention, were well known to the 
ancients ; and more than two centuries ago the 
practice was recommended to the farmers of our 
country by Lord Bacon ; 44 meadow-watering,” 
according to the statements of this illustrious per- 
sonage, (given in his Natural History, in the arti- 
cle Vegetation,) 44 acts not only by supplying useful 
