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impalpable state of division, i. e . the stiff clays 
and marles, are improved by burning; but in 
coarse sands, or rich soils containing a just mixture 
of the earths, and in all cases in which the texture 
is already sufficiently loose, or the organizable 
matter sufficiently soluble, the process of torrefac- 
tion cannot be useful. 
All poor siliceous sands must be injured by it; 
and here practice is found to accord with theory. 
Mr. Young, in his Essay on Manures, states, “ that 
he found burning injure sand and the operation 
is never performed by good agriculturists upon 
siliceous sandy soils, after they have once been 
brought into cultivation. 
An intelligent farmer in Mount’s Bay told me, 
that he had pared and burned a small field several 
years ago, which he had not been able to bring 
again into good condition. I examined the spot, 
the grass was very poor and scanty, and the soil an 
arid siliceous sand. 
Irrigation , or watering land , , is a practice which, 
at first view, appears the reverse of torrefaction ; 
and in general, in nature, the operation of water is 
to bring earthy substances into an extreme state of 
division. But in the artificial watering of meadows, 
the beneficial effects depend upon many different 
causes, some chemical, some mechanical. 
Water is absolutely essential to vegetation ; and 
when land has been covered by water in the winter, 
or in the beginning of spring, the moisture that 
has penetrated deep into the soil, and even the sub- 
soil, becomes a source of nourishment to the roots 
