Thus, the greensand which lies under the chalk, and appears near the surface in several parts of Britain, consists of silicious, argillaceous, and calcareous earth, intimately combined and in a high state of subdivision, and yet not forming a compact paste with water so as to dry in hard lumps, but having rather the loose appearance and granula tion of fine sand, whence its name. On this soil are found the finest wheats ; but such is the variety of its form as it approaches towards the chalk or crystallised sand, or the plastic clay, that the soils which it forms have every degree of texture, from loose sands to stiff marls, whose chief use is to mix with other soils and improve them. In general however it may be said that the soils of which the greensand forms a considerable part are productive and easily cultivated, and that they repay the labour and manure expended on them better than most others. A narrow strip of this sand crosses Bedfordshire, and in the neighbourhood of Sandy and Biggleswade are raised some of the finest culinary vegetables which come to the London market. This sand, though light in appearance, and very easily worked, contains much of the impalpable substance mentioned before ; and this, with careful cultivation and manuring, makes it peculiarly suited for gardens as well as for corn-fields. In its natural state it is easily distinguished from other sands by certain dark particles in it, which give it the greenish hue from whence it has been called greensand, and also by its effervescence with strong vinegar or any other acid.
Chalk is perhaps the mineral most widely spread throughout Britain. The chalk formation of itself forms a very poor and barren soil. In the course of ages the surface of the chalk has been covered with a thin coating of soil, consisting of chalk and organic matter chiefly. On this soil the finest and most aromatic plants are found, but of small dimensions, affording a sweet abort pasture, much relished by sheep. The constant treading in of the dung of the sheep, and the stimulating effect of their urine, gradually increase the quantity of vegetable and animal matter ; and thus the turf becomes close and rich : but if this thin coat be disturbed by the plough and mixed with the chalk below, it will, after one or two tolerable crops of corn, be reduced to its original sterility ; and it requires ages to restore the fine pasture which once covered it. Such is the case with those hills which are called the South Down Hills, in Sussex and Wilt shire, on which are bred the excellent sheep which bear that name.
But the chalk has in many places been carried down by the rains and transported in a comminuted state to the sandy or clayey valleys around them, and by the mixture has greatly improved both, forming various loams and merle in themselves highly fertile, or very useful in increasing the fertility and texture of other soils. Chalk has the
peculiar property of neutralising acids of every description, and of preventing their formation in the soil by the fermentation of vegetable substances ; while it assists in that slow decomposition which causes the evolution of carbonic acid, and thereby assists and invigorates veptation. The presence of carbonate of lime, if it does not exceed a third part, and if it is intimately blended with alumina and silica, is always a sign of fertility, especially when loose sand is tnixed with it, KO as to form one-half of the whole soil. This is called a light calcareous loam, and is usually found ou the slopes or around the base of chalky hills.
The Weald clay consists of very minute particles of alumina and silica, forming a tough unctuous earth, fit for the growth of oaks, with very few stones or visible particles. This soil is found in Sussex and Kent chiefly. The plough cuts it into continuous slices, when it can be ploughed, which is only in a certain state of moisture; for when it is dry the surface is as hard as a rock, while the subsoil is continually moist, the water being unable to pass through its pores. It has the most unpromising aspect, drying into hard lumps like brick, and appa rently incapable of being brought to euch a state of mellowness as to admit the seed or cause it to vegetate; yet this stubborn soil may be rendered fertile by tillage, draining, and exposure to frost in winter ; and its tenacity may be corrected by the application of lime, ashes, and other substances, especially fresh stable-dung, which interpose and prevent the clods from re-uniting into one tough impervious mass. Lime and chalk do this most effectually ; and when the weald clay has been brought to a looser texture, it produces beans, wheat, oats, and clover in great perfection.
The system of complete under-dr•aining by parallel drains, at the distance of from 10 to 20 feet, which carries the moisture into the surrounding ditches, has iu many instances so greatly improved the weald clays, that those who had formerly attempted to cultivate them can scarcely believe their eyes when they see the abundant crops pro duced. Subsoil ploughing has also done wonders after complete draining, in some cases rendering the soil so mellow and loose as to allow of the cultivation of turnips, especially the Swedish. As clay soils predominate in England, and their improvemcut lies been almost despaired of, it is of great importance that it should be generally known that no soils repay the coat of improvement better than clays, provided the surface be such as to admit of perfect draining.