SOILS. 17 



tion, they must hold, and in a form fitted to its support, silex t 

 alumina, carbonate of lime, sulphate of lime, potash, soda, 

 magnesia, sulphur, phosphorus, oxide of iron, manganese, 

 chlorine, and probably iodine. These are called the inor- 

 ganic or earthy parts of soils* as they are found almost 

 exclusively in combination witn earths, salts, or minerals. 

 They however, constitute from less than 0.5 (one half of one) 

 to over 10 per cent, of all vegetables. In addition to these, 

 fertile soils must also contain carbon, oxygen, nitrogen and 

 hydrogen, which are called the organic parts of soils, from 

 their great preponderance in vegetables and animals, of 

 which they constitute from about 90, to over 99 per cent, 

 of their entire substance. 



CLAY SOILS THEIR CHARACTERISTICS AND TREATMENT. 

 Clay soils are usually denominated cold and wet, from 

 their strong affinity to water, which they generally hold in 

 too great excess for rapid or luxuriant vegetation. The 

 alumina which exists in clay, not only combines with water 

 forming a chemical compound, but the minute division of 

 its particles and their consequent compactness, oppose seri- 

 ous obstacles to the escape of such as comes in contact with it. 

 Hence, the necessity of placing it in a condition to obviate 

 these essential defects. 



The most effectual method of disposing of the surplus 

 water in clay soils, is by underdraining. This draws off 

 rapidly, yet by imperceptible degrees, all the excess of water, 

 and opens it to the free admission of atmospheric air ; and 

 this, in its passage through the soil, imparts heat and such of 

 the gases it contains, as are useful in sustaining vegetation. 

 When these are not constructed, open drains should be 

 formed wherever water stands after rains. The slight ele- 

 vation and depression of the surface made by careful plow- 

 ing, will probably be sufficient, if they terminate in some 

 ravine or artificial ditch, and have size and declivity enough 

 to pass off the water rapidly. 



Clay soils are greatly improved by coarse vegetable ma- 

 nures, strp.w, corn-stalks, chips, &c., which tend to the sepa- 

 ration of its particles. The addition of sand is very benefi- 

 cial, but this is too expensive for large fields. Lime is also 

 a valuable material for a clay soil, as by the chemical combi- 

 nations which are thereby induced, the extreme tenacity of 

 the soil is broken up ; while the lime adds an ingredient of 

 fertility, not before possessed by it, perhaps, to an adequate 

 extent. Gypsum has the same effect, in a more powerful 



