AGRICULTURE. 145 



trates, and the greater the extent of its diffusion. This 

 class of laud therefore, so tilled, is not so readily ' satu- 

 rated ; ' the water does not stagnate on the surface so 

 as to stop the circulation of the air and the diffusion of 

 heat through the soil, which are so essential to the life 

 and growth of plants. 



On very low lands, in addition to deep tillage, it is 

 requisite to facilitate the exit of the water by deep fur- 

 rows, open drains, and ditches. 



I do not enter on the very important and highly in- 

 teresting subject of regular draining, as being from its 

 costliness out of the reach of the infant husbandry of the 

 country. I may, however, remark that it is nothing more 

 than an advanced system of realising ends which I have 

 just pointed out, viz. the leading down of the rainfall 

 waters to a greater depth in the soil, and the carrying off 

 any excess which would otherwise stagnate in it. 



V. 



As the mechanical and physical action of soil is resi- 

 dent in and in relation to its general composite mass, so 

 its chemical action has relation to certain elementary sub- 

 stances, or minerals, intermixed in its substance, each of 

 which possess certain affinities for others in greater or less 

 degree, governed and determined by special physical 

 conditions and influences. Under these influences there 

 is a dissolution of certain chemical combinations and the 

 formation of others. In the laboratory of the mass of 

 the soil, all those changes, solutions, and combinations are 

 effected which dispose and prepare the inorganic or 

 mineral elements forming part of its substance to enter 

 on functions which form part of the cycle of organism or 



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