PRACTICAL AGRICULTURE. 11 



exists in the state of fine divisions, are comparatively 

 fertile. 



2. Soils in which the quantity of sihceous.sand is 

 large are comparatively infertile ; while soils in which 

 the sand is fine and only partially siliceous, are compare 

 atively fertile. 



3. Iron exists in all spils, but does not influence 

 their fertility in proportion to its larger or smaller quan- 

 tity. 



4. An excess of the acid combinations of the oxide 

 of iron, and certain other saline bodies, is hurtful to veg- 

 etation. 



6. Carbonate of hme exists in the best soils, and, gen- 

 erally, though not always, in larger quantity in the bet- 

 ter than in the inferior soils. 



6. Certain earths possess the power of combining 

 chemically with animal and vegetable matter, and of 

 retaining it for a longer or shorter time. Thus, alumina 

 and lime form certain compounds of greater or less in- 

 solubility with animal and vegetable matters, while 

 silica will not enter into the same combinations ; and 

 hence it is that aluminous and calcareous soils retain 

 for a longer time the manure applied to them than sili- 

 ceous soils. 



7. When w^ater is in excess in the soil, and when 

 vegetable matter is present, acid is formed which is 

 injurious to the productive powers of the soil. Far- 

 mers are familiar with this effect, and say that the soil 

 is soured. 



8. Soils, besides absorbing moisture from the air, ap- 

 pear to absorb carbon and other matters nutrimental to 

 plants. 



MEANS OF INCREASING THE PRODUCTIVE POWERS 

 CF SOILS. 



1. Supply the soil with those organic and earthy sub- 

 stances which may be required. 



2. Alter its texture, depih, and properties, by tillage 

 and other means. 



