diffused and finely divided; and it is probably 
more useful to land than any calcareous substance 
in its natural state. 
The most considerable fact made known, with re- 
gard to limestone within the last few years, is owing 
to Mr. Tennant. It had been long known, that apar- 
ticular species of limestone, found in different parts 
of the North of England, when applied, in its burnt 
and slacked state, to land, in considerable quanti- 
ties, occasioned sterility, or considerably injured 
the crops for many years. Mr. Tennant, in 1800, 
by a chemical examination of this species of lime- 
stone, ascertained, that it differed from common 
limestones, by containing magnesian earth ; and 
by several experiments, he proved, that this earth 
was prejudicial to vegetation, when applied in 
large quantities in its caustic state. Under com- 
mon circumstances, the lime from the magnesian 
limestone is, however, used in moderate quantities 
upon fertile soils in Leicestershire, Derbyshire, and 
Yorkshire, with good effect ; and it may be applied 
in greater quantities to soils containing very large 
proportions of vegetable matter. Magnesia, when 
combined with carbonic acid gas, seems not to be 
prejudicial to vegetation, and in soils rich in ma- 
nure, it is speedily supplied with this principle 
from the decomposition 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 husbandry capable of elucidation by chemical 
principles. 
The chemical theory of fallowing is very simple, 
c 8 
