Soils and Manures. 31 



These grand classes of soils, running into each other by 

 imperceptible gradations, and being variously modified, may be 

 considered as embracing every variety found on the face of the 

 globe. 



3. Loamy Soils. — A mixture of from fifteen to sixty per 

 cent, of sand with clay forms a loamy soil. If the sand do not 

 exceed thirty per cent., it is called a clay loam; more than 

 thirty per cent.lconstitutes it a sandy loam. 



4. Calcareous Soils. — Calcareous soils are those in which 

 lime, exceeding twenty per cent., becomes the distinguishing 

 constituent. Calcareous soils may be either calcareous clays, 

 calcareous sands, or calcareous loams, according to the propor- 

 tions of sand or clay which may be present in them. 



6. Marly Soils. — Soils containing lime, but in which the 

 proportion does not exceed twenty per cent., are sometimes 

 called marly. 



6. Vegetalle Molds, — When decayed vegetable matter exists 

 in so great proportion as to give the predominant character to 

 a soil, it receives the name of vegetable mold. Vegetable 

 molds are of various kinds, and may be either clayey, sandy, or 

 loamy, according to the predominant character of the earthy 

 admixtures. 



7. Alluvial Soils. — AUmdal soils are such as have been 

 formed by the washings of streams. They are generally loamy, 

 and very fertUe. 



Besides their principal component parts, every soil must 

 contain, in greater or less quantities, all the elements which 

 enter into the composition of vegetables. They may have cer- 

 tain substances which are not necessary to vegetable life, and 

 such as are necessary may be in excess ; yet to sustain a healthy, 

 prolific vegetation, they must hold, and in a form fitted to its 

 support, silex,, alumina^ carlonate of lime, sulphate of lime, 

 potash, soda, magnesia, sulphur, phosphorus, oxyd of iron-, 

 manganese, chlorine, and probably iodine. These are called 

 the inorganic or earthy pai'ts of soils. In addition to these, 

 fertile soils must contain carlon, oxygen, nitrogen, and hydro- 



