42 GARDENING FOE THE SOUTH. 



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 successful 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 mat- 

 ter 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 argil- 

 laceous, 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, ami 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. 2. 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, loam}' and sandy, and also contain, or be 

 destitute of, calcareous matter. 



Humus has the property of producing a constant sup- 

 ply of carbonic acid by slow combination with oxygen. 

 It aids greatly in keeping a soil in an open state, so as to 



