COMPOSITION OP SOILS AND THEIR ACTION. 45 



CHAPTER IV. 



COMPOSITION OF SOILS AND THEIR ACTION. 



• 

 Arable Soils. — Proper Proportions. — Productiveness. — Tenden- 

 cy to Deteriorate. — Necessity of Manures. — Value of a Rota 

 tion in Cropping. — Reasons for the Practice. 



A. KNOWLEDGE of the earths that enter into the 

 composition of, and which most essentially modify 

 the soil he cultivates, is necessary to every farmer ; 

 as such knowledge greatly facilitates its proper man- 

 agement, in the crop to be raised, the manure to be 

 appliedf and the time of its application. Fortunate- 

 ly for the farmer, the kinds of earth that form the 

 best soils for cultivation are few in number, three 

 being sufficient for every valuable object, and more 

 being frequently found injurious rather than benefi- 

 cial to the purposes of the agriculturist. These 

 three earths are silcx, which is the basis of all sand, 

 and is found pure in rock crystal ; lime, which is 

 the basis of all the limestone rocks, marbles, and 

 gypsum, and is found nearly pure in Iceland spar 

 and primitive marble ; and alumme, which is the 

 base of ail clayey soils and the great variety of clay 

 rocks, and is found nearly pure in the best speci- 

 mens of the alum of commerce. 



Of these three substances, soils devoted to agri- 

 culture are nearly always formed, though they exist 

 in very different proportions, and are always more 

 "'~^or less mingled with decomposed animal or vegeta- 

 ble matter. Vegetation will indeed take place in 

 any one of these substances, if water and the prop- 

 er degree of warmth be present, but it will be very 

 feeble and inefficient. On the contrary, when com- 

 bined in proper proportions, and the necess iry quan- 



