SOILS. 19 



Limestone, in burning, loses about half its weight; but the 

 quick-lime thus produced, possesses a strong affinity for water, 

 which it will absorb from the atmosphere. When water is 

 applied in quantity, it is absorbed by the lime, with a great 

 evolution of heat, and this is the process of slacking so well 

 known. The lime thus combined with water attracts carbonic 

 acid, and again becomes carbonate of lime. It differs from its 

 original state in its external characters only, and in the lesser 

 degree of cohesion of its parts, for otherwise the substances are 

 the same. 



As an ingredient of the soil, lime is closer than sand, but 

 much less adhesive than clay. It occupies therefore a middle 

 region, as it were, between the two, free from their imperfec- 

 tions, and blending their common qualities. It is also a neces- 

 sary ingredient in the organization of plants, many of which 

 cannot reach their full vigour and luxuriance without it. 

 Wheat in particular requires its presence, and where it does 

 not already exist in the soil, it ought to be supplied, at what- 

 ever expense, for the production of superior crops. 



Magnesia earth, like lime, is usually found in combination 

 with carbonic acid but even in this, its natural state, it exists 

 in such very small quantities in soils, and is found so rarely, 

 and the functions it performs in the economy of vegetation so 

 doubtful, that its name is an almost useless addition to the list 

 of the earths of agriculture. 



All the earths, individually, when as pure as they are ever 

 furnished by nature, are entirely barren, nor would any addi- 

 tion of putrescent manures, enable either of the earths to sup- 

 port healthy vegetable life. The mixture of the three earths, 

 first enumerated, in due proportion, will correct the defects of 

 all, and with a sufficiency of animal or vegetable matter, a soil is 

 formed. Such is the natural surface of almost all the habitable 

 world; and though the qualities and value of soils are as va- 

 rious as the proportions of their ingredients, yet they are 

 mostly so constituted that no earthy ingredient is so abundant 

 but that the texture of the soil is mechanically suited to the 

 production of some valuable crop. There is no mode of im- 

 proving the fertility of a soil, so permanently efficacious, as 

 that of adding to the land a proportion of the earthy ingredient 

 of which it is naturally deficient. 



Some plants require a degree of closeness, and others of 

 openness, in the soil, which would cause other plants to decline 

 or perish. As the qualities and value of soils depend on the 

 proportion of their ingredients, and the grand point in agri- 

 culture being to obtain a mixture of the earths best calculated 

 to produce the greatest variety of the most valuable crops, we 



