Soil, strictly speaking, is the ground or earth w herein crops of every kind are produced; and we notice it in this way, merely to distinguish the surface from the under stratum or subsoil on which the surface is in- cumbent. The value or worth of that part of the earth, which is the object of cultivation, depends materiall upon the nature of the under stratum ; because, when the latter is close or extremely retentive of moisture; the expense and hazard of cultivating the surface is considerably increased, whist the growth of plants cul tivated upon it is much abridged and impeded, partictr tally in adverse seasons.
The nomenclature of agriculturists, with regard to soils, being variable and indistinct, it is Fl difficult task to describe them, or to mark with any degree of accuracy the shades which distinguish one from another, so nearly are many of them connected. Generally speak ing, the component parts of soil, whatever may be the colour, are argill, sand, water, and air ; for into these original principles may all earths he reduced, however blended with apparently foreign substances. Argill is the soft and unctuous part of ( lay. The primitive earths, argill and sand, contain each, pC in nearly equal degrees, the food or plants ; but in their union the purposes of vegetation are most completely answered. The precise quantities of each necessary to make this union perfect, and whether they ought to be equal, it is neither very easy nor very material to ascertain, since that point is best determined in practice, when the soil proves to be neither too stiff or adhesive, from the super-abundance of clay. nor of too too' e and weak a texture. from an over quantity of sand in its composi tion. The medium is undoubtedly best ; but an excess towards adhesion is obviously most safe. A stiff or strong soil holds the water which falls upon it for a long time, and being capable of much ploughing, is natt- rally for c airy Mg the most valuable ara ble crops. A light soil, or one of a texture feeble and easily broken, is, on the contrary., soon exhausted by aration, and requires renovation by grass ; aliens ise it cannot be cultivated to advantage.
Dr NV. Diekson, hi his excellent treatise on agricul ture, says, with much truth, that the soils of this coun try have been described under numerous heads, and particularized by an useless variety of local terms. According to him, however, they may be considered and characterized, as far at least as is necessary lot' practi cal purposes, under the distinctions of Clayey, Loamy, Chalky, Sandy, Gravelly, and Peaty or Mossy. Each
of these diversities of course comprehends several varieties, according to the nature and preponderance of the different sorts of materials of which they are composed.
Other writers speak of a soil which they call garden mould ; but this, being entirely of artificial creation, ought not to be ranked amongst the natural or origi nal soils.
In a work of this kind, it may be proper to arrange British soils into four different classes, namely clay, sand, gravel, and peat earth ; as to one or other of these elisses each of the numerous varieties in the British isles is allied, though in many cases the degree of affinity is not easily ascertained. Loam has generally been considered as an original earth, though we are dis posed to view it as an artificial soil, produced by calca reous matters, and animal and vegetable manures. The strongest clay may, in process of time, be converted into a loam, by repeated applications of these substances ; and the richness or freeness of that loam will depend entirely upon the quantity of manure with which it has been supplied. Sandy soils may also be converted into light loarns, by the application of lime, chalk, marl, and especially clay. Even peat may be converted into a black soft loam, and in various ways rendered fertile and productive. From these circumstances, a degree of confusion prevails respecting the nature and proper ties of soils, which renders the subject more difficult than at first sight might be expected. Even the admix ture of surface and subsoil, by deep ploughing, creates a change of considerable magnitude.
A clay soil, though distinguished by the colour which it bears, namely black, white, yellow, and red, differs from all other soils, being tough, wet, and cold, and con sequently requiring a good deal of labour from the hus bandman before it can be sufficiently pulverized, or placed in a fit state for bearing artificial crops of corn or grass. Clay land is known by these qualities, or properties. It holds water like a cup, and once wet ted does not soon dry. In like manner, when thoroughly dry, it is not soon wetted ; if we except the varieties which have a thin surface, and are the worst of all to manage. In a dry summer, clay cracks, and shows a surface full of small chinks, or openings. If ploughed in a wet state, it sticks to the plough like mortar, and in a dry summer the plough turns it up in great clods, scarcely to be broken or separated by the heaviest roller.