SOILS THEIR CHARACTERISTICS. 23 



most useful plants. There are some plants, however, as 

 the Kalmia, to which its presence, to any appreciable extent 

 in soils, is injurious. Any one of the foregoing soils that 

 contains from five to twenty per cent of lime is classed 

 as marly, (as a marly clay, a marly loam, etc. ) When it 

 contains over twenty per cent, it is classed as calcareous. 

 A small percentage only of lime is required for the suc- 

 cessful growth of plants. Marly soils, other things being 

 equal, are the best adapted to fruit trees and wheat. They 

 are also classed as argillaceous, loamy, sandy-loamy, and 

 loamy-sandy marls, etc., according to the relative amounts 

 in them of clay and sand ; while if they contain above 

 five per cent of humus (vegetable matter in a state of 

 decay,) they are classed as humus marls, which may be 

 also argillaceous, if containing fifty per cent of clay ; loamy, 

 if from thirty to fifty per cent ; and sandy, if less than 

 thirty per cent of clay. 



Calcareous Soils (which contain more than twenty per 

 cent of carbonate of lime) also are classed in the same 

 manner with marly soils, according to the relative amounts 

 of clay, sand, and humus they contain as argillaceous, or 

 loamy calcareous, etc. 



Organic Soils. Shell marls, though of organic origin, 

 are naturally classed with the calcareous soils. The other 

 organic soils are mainly of vegetable origin, resulting from 

 the decay of plants, and are named humus soils. This 

 last class is of three orders : 1st. Soluble mild humus, 

 that is, vegetable mould in a fit condition for the nourish- 

 ment of the plants which grow in it, such as thoroughly 

 rotted peat, black or leaf-mould. 2d. Acid humus, which 

 contains a free acid, injurious, if not destructive, to most 

 plants. 3d. Peat or other fibrous vegetable matter, which, 

 though free from acidity, is not yet in a proper condition 

 to impart nourishment to plants. Humus soils may be 

 argillaceous, loamy and sandy, and also contain, or be des- 

 titute of, calcareous matter. 



