ELEMENTS OF AGRICULTURE. 
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8f < If a sandy soil covers a clay sub-soil, it is much less 
exposed to the evil effects of drought, on account of the 
moisture retained beneath it; and by deep ploughing the 
clay may be mixed with and thu^ improve it. 
8G. These mixtures of the sub-soil and soil are not the 
only means that the farmer possesses of preserving in the 
land the moisture necessary to the vegetation of plants. 
Frequent working gives also to land the property of retain¬ 
ing moisture, and this is the case as well with a stiff as with 
a sandy soil. The cause of this has not yet been well ex¬ 
plained, but it is so: and it is in contradiction to an 
opinion entertained by many, that frequent working in 
limes of drought is injurious to the crop. 
87. As a clay sub-soil is suitable to sandy land, just so is 
a sandy sub-soil favorable to a surface containing much 
clay. It permits the infiltration of the superabundant 
moisture, and may ameliorate the soil if mixed with it. 
88. But a sandy soil, based upon a sub-soil of the same 
nature, being entirely too permeable to moisture, must 
suffer much from drought, and yield but indifferent crops. 
There is too great waste of manures, as their liquid parts 
sink too deep. 
89. When the soil is devoid of carbonate of lime, and 
the subsoil is calcareous, a mixture of the two by deep 
ploughing is evidently beneficial. Stiff soils particularly 
will profit by this mixture ; for at the same time they will 
lose a portion of their tenacity, become more favorable to 
vegetation, and rendered easier to work. But the carbon¬ 
ate of lime in the sub-soil must be in an earthy state, and 
not in the form of stones, a few only of which, the schis» 
tous, can, as we have seen, become friable on the surface. 
90. From what precedes, we perceive that there are 
many cases in which deep ploughingcan improve the soil, 
and increase its products. It is true that, in certain cases, 
these workings appear in the first years to injure rather 
