SOILS. 549 



formed of stiff clay, are, as a rule, most expensive to cultivate, requiring much 

 drainage and top-dressing with marl or lime. They are best adapted for pasture 

 and dairy-farmimg, although wheat and beans are largely grown on them. The 

 loams, and especially the calcareous loams, form the richest soils. The light 

 sandy and gravelly soils are often barren, forming heaths and warrens which offer 

 a pleasant contrast to the cultivated scenery. Over many districts the soil is of a 

 "mixed" character, varying constantly from field to field; and this is generally 

 •due to the irregular character of the sub-strata. This is more especially the case 

 with the Glacial Drifts, which are included under the comprehensive name of 

 Superficial Deposits, the importance of whose influence on Agriculture was so 

 persistently urged by Joshua Trimmer. 



In Agriculture, moreover, the elevation of the land, the rainfall, and other 

 conditions are naturally of great importance.^ The depth of soil is liable to vary, 

 not only in accordance with the nature of the underlying rocks, but also with the 

 shape of the ground and the influence of rain in removing it. On sloping ground 

 the soil is liable to variation from the material washed down by rains ; while in 

 some regions composed of Granite, Slate, hard Sandstone, and Limestone, the 

 rocks stand out in bare crags. 



Made Soil. — Under London and other large cities and towns a considerable 

 accumulation of artificial soil is generally met with in sinking wells, in digging 

 foundations, etc. This 'made soil' comprises the materials of old buildings, and 

 road-metal, as well as rubbish and gravel that have been employed to fill up low 

 damp ground. Burnt earth, a relic of the Great Fire of 1666, has in some 

 instances been observed under London, in the ' made soil,' which in places is nearly 

 30 feet thick. ^ 



JMoiild. — The formation of mould or humus is due partly to the decay of 

 vegetable matter, and to meteoric influences, but very largely to earth-worms 

 building up a soil as it were by the material ejected from them. As first taught by 

 Darwin, its homogeneous nature, when overlying different kinds of subsoil, is 

 due to the labours of worms in casting up the soil, and thus allowing stones and 

 other solid fragments to subside ; so that in old pasture-land not a single stone 

 perhaps will be found within some inches of the surface, and one can understand 

 why farmers are averse to breaking up such tracts.'^ 



Peaty earth is sometimes formed on heaths and commons where the decay of the 

 plants gives rise to an accumulation of partly decomposed vegetable fibre, mixed 

 with sand. On low-lying alluvial ground, the soil is often black and peaty, in 

 some cases originating from the weathering of a mass of peat below, in other cases 

 being a swampy accumulation of decaying vegetable matter, mixed with alluvial 

 debris. This forms what is called Bog earth. (See also Peat, p. 522.) 



Rai)iwash. — The material washed down from higher to lower grounds, on the 

 slopes of hills and mountains, is termed ' Kainwash ' or 'Landwash,' to distinguish 

 it from the Alluvial deposits of streams. It naturally varies from coarse ' Angular 

 detritus ' to sand, loam, and clay, but it is essentially of local origin. With it may 

 be included the ' Head ' previously noted (see p. 495), and other forms of ' talus ' 

 like the ' Screes ' of loose detritus accumulated at the foot of steep scarps of rock, 

 while Landslips on a small scale are intimately associated. (See sequel.) 



Clay-ioith- Flints. — This consists of stiff brown and red clay containing large 

 unworn flints, and at its base displaying generally a few inches of black clay with 

 black-coated flints. Occasionally pebbles of flint, quartz, and other rocks, occur 

 in the accumulation, due to some former capping of Drift gravel or of Tertiary 

 beds. 



TheClay-with-flints is mainly confined to the Upper Chalk tracts, for, as pointed 



' F.J. Lloyd, Science of Agriculture, 1S84 ; J. Morton, Nature and Property 

 of Soils, ed. 4, 1843 ; J. Bravender, Indications of Fertility or Barrenness of the 

 Soil, Journ. R. Agric. Soc. v. ; Trimmer, Practical Geology, p. 22 ; Q. J. vii. 19, 

 37 ; Journ. R. Agric. Soc. xii. 445 ; North British Review, Feb. 1852. 



^ Whitaker, Surface-Geol. London, 1S67 (in Report of Medical Officer of the 

 Privy Council for 1866). 



» Proc. G. S. ii. 574, T. G. S. (2), v. 505; Formation of Vegetable Mould, 1881. 



