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binations be poisonous to them; and it is known that 

 lime and magnesia are both noxious to vegetation, 

 unless combined with this principle. 



All soils that contain too much dead vegetable 

 fibre, and which consequently lose from one third to 

 one-half of their weight by incineration, and all such 

 as contain their earthy constituents in an impalpable 

 state of division, i. e. the stiffclays and marles, are im- 

 proved by burning; but in coarse sands, or rich soils 

 containing a just mixture of the earths; and in all ca- 

 ses in which the texture is already sufficiently loose, 

 or the organizable matter sufficiently soluble, the pro- 

 cess of torrefaction cannot be useful. 



All poor -siliceous sands must be injured by it; 

 and here practice is found to accord with the 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, die benefi- 



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