6 ORIGIN AND KINDS OF SOILS, CONSIDERED 



loams consist of clay with a proportion of sand and organic matter ; 

 they produce large crops, but become hard and baked on the surface 

 after heavy rains followed by drought. Stiff adhesive clays contain 

 in their composition little or no sand or lime, and are almost without 

 organic matter. All clayey loams are later than sandy loams. 



Loams are the best soils, and are characterized according to the 

 earths which prevail in them, as a sandy loam, &c. ; according to their 

 degree of friability, as a free loam, a stiff loam, &c. ; or according to 

 both, as a free calcareous loam, &c. These soils, with reference to 

 geology, are generally found on the sides of valleys, along the bases of 

 hills or mountains, or on the banks of upland rivers. Mechanically, 

 they are of a texture easily penetrated by all the implements of 

 culture, and not liable to become hard on the surface, and crack after 

 heavy rains followed by drought ; chemically, they contain clay, sand, 

 calcareous matter, and humus ; and with reference to vegetation, 

 produce abundant crops in all ordinary seasons, with moderate supplies 

 of manure. 



In general, much more depends on the texture of a soil and its 

 capacity for retaining or parting with water and heat, than on its 

 chemical composition. Soils have been found consisting chiefly of 

 clay, others chiefly of calcareous earths ; some in America, without 

 calcareous earths; and all producing good crops for a series of years. 

 Nevertheless, it has been found that no soil will remain fertile for many 

 years that does not contain lime in some form naturally, or is not 

 liberally supplied with manure containing animal matter, one ingredient 

 of which is lime in a state of phosphate. 



Subsoils. Next in importance to the texture of a soil, is the nature 

 of the subsoil or substratum on which it rests ; because on the texture 

 and other circumstances of this subsoil depends, in a great measure, 

 the capacity of the surface-soil for retaining or parting with water or 

 heat. The worst subsoils are those of clay kept moist by subterraneous 

 water; and the best, those of clay resting on gravel or porous rock; 

 because these retain a useful degree of moisture, and admit of in- 

 creasing the surface- soil to any depth which may be required for 

 culture. Sandy and gravelly subsoils, with but a thin coating of sur- 

 face-soil over them, are not sufficiently retentive of moisture ; and 

 chalky subsoils are generally cold. 



The surface of soils has, perhaps, as powerful an influence on their 

 natural fertility as the subsoil ; because on the inclination of the sur- 

 face depends, in a considerable degree, the moisture retained by the 

 soil, and consequently its fitness for the growth of plants. Too steep 

 a slope throws off the rain with too great rapidity, and thus deprives 

 the soil of a sufficient supply of water during dry seasons ; while a flat 

 surface will retard its drainage and occasion loss of heat by evaporation. 

 These natural results of a steep incline and a flat surface may be greatly 

 modified by the depth of the soil and surface stirring, the colours, &c. 

 The colour of the surface of a soil exercises some influence on its heat. 

 A dark- coloured soil will be sooner heated by the rays of the sun than a 

 light-coloured soil ; but it will also part with its heat more rapidly 



