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THE planter's GUIDE. 



animal or vegetable matter. When equally mixed with 

 it, they prevent it from too rapid a decomposition ; and 

 they also supply the soluble parts in their due proportions. 



Kirwan, in his Geological Essays, has shown that the 

 fertility of a soil in a great measure depends on its 

 capacity to retain water. The power of the soil to 

 absorb water by cohesive attraction depends, in a con- 

 siderable degree, on the division of its parts. The more 

 these are divided, the greater their absorbent power. 

 Hence the great importance of friability or looseness of 

 texture, so that moisture may have free access to the 

 fibres of the roots, that heat may be readily conveyed to 

 them, and that evaporation may proceed without obstruc- 

 tion. These benefits are usually attained by the presence 

 of sand. As alumina possesses, in an eminent degree, all 

 the powers of adhesiveness, and silex those of friability, it 

 is obvious that a mixture of those earths, in suitable pro- 

 portions, would furnish every thing that could be wanted 

 in the most perfect soil. In a soil so constituted, water 

 would be presented to the roots by capillary attraction. 

 It would be suspended in it, says Griesenthwaite, in the 

 same way as in a sponge, that is, in a state not of aggre- 

 gation, but of minute division, so that every part might 

 be moist but not wet.*^ Hence the best soil, whether for 

 wood or agricultural crops, obviously is one that is at 

 once loose and deep, containing the most alumina and 

 carbonate of lime, so as to act with the greatest chemical 

 energy in the preservation of manures. f 



Trees, far more than agricultural crops, require depth 

 of soil to raise them to perfection : the eff'ect of climate 

 appears much less necessary in giving them their greatest 

 magnitude. Accordingly, notwithstanding the insularity 



* New Theory of Agriculture. 



t Note I. 



