ELEMENTS OF AGRICULTURE. 
75 
harder than the rest of the clay, are finally separated from 
it, and pass into the sub-soil. It has, however, the advan¬ 
tage of sand in being cheaper. (We will explain the pro¬ 
cess of calcination under the head Paring and Burning.) 
52. Ploughing at the proper season, the application of 
lime, and a sufficient quantity of manure, are the best 
means of ameliorating stiff soils. As the action of frost 
usually renders these lands more friable, they should be 
broken up in the autumn. 
53. The same reasons that prevent the improvement of 
stiff lands by means of sand, hold good against the im- 
provement of sandy ] ands by the use of clay. There are, 
however, but few cases in which the improvement of 
purely gravel or sandy lands will pay at all. 
QUESTIONS. 
1. Can sand and clay serve as mutual improvers ? 
2. Why is it that sand does not render stiff lands more friable? 
3. What other reason is there for not using sand as an improver of stiff 
soils ? 
4. In what cases would it be proper to mix sand and clay ? 
5. Is there not another method of improving stiff soils ? 
6. What are the best means to improve stiff land ? 
7. Why should not gravelly and sandy lands be improved by the appSteS' 
lion of clay ? 
