ELEMENTS OF AGRICULTURE. 
39 
rated grasses and leguminous herbage plants, though they 
are not so quickly covered with the natural herbage plants 
of the soil, when laid down to perennial pasturage, as the 
lighter soils. 
3). Clays, like other soils, approach to their most per~ 
feet condition as they advance to that state which has been 
termed loam. The effect of judicious tillage, and of the 
application of manures, is to improve the texture of such 
soils, as well as to enrich them. Thus, clays in the neigh¬ 
borhood of cities become dark in their color, and less cohe¬ 
sive in their texture, from the mixture of animal and vege¬ 
table matter; and thence acquire the properties of the 
most valued soils of their <*lass. 
QUESTIONS. 
1. What is the composition of clay 9 
2. What is alumine 1 
3. Why are clay soils sometimes r#d ? 
4. What is their distinguishing character 1 
5. What manufacture is clay valuable for, and why ? 
6. Are they as easily worked as other soils ? 
7. What is said about the application of manures to clays ? 
8. What class of plants succeed best hi them ? 
9. Why are they unprofitable to cultivate ? 
10. They are unfitted for the growth of what plants 1 
11. Clay soils are unequalled, when of fine quality, for the production of 
what? 
12. They yield large returns of what ? 
13. What is the effect of manures and judicious tillage upon their texture 1 
14. What is the effect of animal and vegetable manures upon their color? 
LESSON y. 
CARBONATE OF LIME. 
31. As we have indicated (No. 9), carbonate of lime is 
formed by carbonic acid and lime. Carbonic acid is a gas 
heavier than air; large quantities of it are thrown off by 
burning charcoal. 
