I. SOILS AND SUBSOILS.

The soils upon which the agriculturist has to operate are usually classified as sandy, sandy or light loams, loams, clayey loams, heavy or retentive clays, marls, calcareous loams, peaty soils, or bog-earths. This classification has reference chiefly to composition and texture, a special chemical composition (silicious, calcareous, &c.) being necessary for the profitable growth of particular crops, and a certain mechanical texture (friable, porous, &c.) suiting best for the permeation of rain and air, and the descent or spreading of special roots and rootlets. Loams, consisting of fertile admixtures of sand, clay, and humus or decayed vegetable matter, may be regarded as typical soils, which become, on the one hand, light, by a preponderance of sand, and on the other, heavy, by a preponderance of clay. But whatever their composition and texture, these soils, geologically speaking, are mainly of two sorts,-soils of disintegration, arising from the waste and decay of the immediately underlying rocks, together with a certain admixture of vegetable and animal debris; and soils of transport, whose ingredients have been brought from a distance, and have no geological connection with the rocks on which they rest. Under the former are comprehended such as arise from the disintegration of limestones, chalks, traps, granites, and the like, and which are directly influenced in their composition, texture, and drainage, by the nature of the subjacent rocks from which they are derived. Under the latter are embraced all drift and alluvial materials, such as sand, shingly debris, miscellaneous silt and clay, which have been worn from other rocks by meteoric agencies, and transported to their existing positions by winds, waters, or ancient glacial agencies. Besides these there are also soils of organic origin, such as peat-earths, and vegetable mould or humus, which is to a great extent also of animal origin or elaboration. Indeed, in all superficial soils there is a certain amount of vegetable and animal matter-the decay of plants, the droppings of animals, the exuvia of insects, the casts of the earth-worm, and the like, conferring upon them that dark, friable, and loamy character so indicative of richness and fertility.

Beyond the soils proper, which come immediately under the plough, there are in most situations a set of subsoils, differing from the true soils, and which cannot be ignored by the farmer. Thus peat may lie upon clay, sand upon clay, common humus on sandy clay, and clay may rest upon shingly

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debris; while in many of our alluvial flats (old lake-sites and estuaries) there may be several alternations of peaty matter, clay, sand, silt, and marl, before the underlying rock-formation is arrived at. In general, the subsoils differ notably in colour and consistence from the soils above them. The true soils are usually of a darker colour, from the larger admixture of humus, while the subsoils are lighter in hue-yellow, red, or bluish, from the greater preponderance of iron oxides. The soils are also more or less friable in their texture, while the subsoils are tougher, more compact, and more largely commingled with rubbly and stony debris. The soils are usually little more than a mere surface covering, while the subsoils may be many feet, or even yards, in thickness.

All these soils and subsoils repose on the rocks below, but it is only where they are immediately derived from these rocks by disintegration that they are materially influenced by this relation. Hence, for agricultural purposes, it is necessary to have two sets of geological maps-one showing the range and disposition of the older rocks, and another exhibiting the disposition of the superficial accumulations by which these are masked. On examining two such maps of any district in Britain, it will be seen that the soils of disintegration occupy limited areas in comparison with those of transport. In all our river-valleys, dales, levels, fens, straths, and carses, the soils are those of transport, and consist of miscellaneous riverdrifts, the alluvia of former lakes and sea - beds, or of the sands, shingles, and bouldery clays of the glacial epoch. Over the higher uplands-largely over carboniferous districts, and on many of the other formations—the drifts of the glacial period are thickly spread; so that it is chiefly on the hilly portions of the Chalk, the Oolite, the Mountain-limestone, the old Slates and Schists, the Traps and Granites, that we find soils of disintegration. And even there, there are many patches of bouldery clay, sand, and shingly drift, whose materials have been brought from other and distant localities.

Soils of Disintegration.

All rock-surfaces, however hard and refractory, break up, in course of time, under the influence of meteoric agencies. Those containing lime are acted upon by the carbonic acid of the atmosphere; those containing iron by the oxygen; and all suffer more or less through frosts, rains, winds, and other kindred forces. These disintegrating agencies are further aided by the root-growth of plants, by the burrowing of worms and other earth-dwelling creatures, and in no small degree by

the acids (humic, geic, and crenic) generated by organic decay. From the hardest granites, basalts, and lavas, to the softest chalks and marls, all are undergoing this disintegration; and the soils thereby produced will vary in depth, composition, and texture, according to the softness and mineral character of the rocks, and the length of time during which they have been subjected to the comminuting forces.

If we take a geological map of the British Islands and turn to the districts coloured as granitic, we shall find them largely covered with a thin cold clayey soil derived from the decomposition of the subjacent granite. Ordinary granite is composed of quartz, some variety of felspar, and mica; and it is the felspar (silicates of alumina, with minor proportions of soda, potash, lime, and iron) which mainly yield this poor moorland covering, the sterility of which is aggravated by its general high elevation, whitish colour, and the impervious nature of the rock on which it rests. We say whitish colour, for, area for area, white soils take in less heat than dark-coloured ones— the former reflecting and the latter absorbing the solar rays. If we turn, on the other hand, to the tracts coloured Trappean, we will find them covered, for the most part, with a dark-coloured, dry, crumbling soil, noted for its fertility and certainty of cropping. This arises from the disintegration of the softer trap-tuffs, amygdaloids, and wackès, and consists, according to the analyses of the late Professor Johnston, of silica, alumina, and lime, with varying proportions of soda, potash, and iron; its fertility and mellowness being augmented by its colour, which absorbs the sun's heat, and by the fissured structure of the rocks beneath, which carries off all superfluous moisture.

In slaty and schistose tracts—that is, those coloured Metamorphic, Cambrian, and Silurian, we find that where these rocks are not masked by diluvial drifts, they have weathered into thin clayey soils of indifferent fertility, partly owing to their elevation, and partly to their retentive texture-green nutritive pastures occurring, as in the southern uplands of Scotland, only where the high inclination of the beds, with their slaty structure, affords a ready and efficient natural drainage. The soft, sandy, and marly strata of the New Red Sandstone break up into a dry fertile soil, especially suited for barley and green crops; while the clayey and marly beds weather down to a stiff retentive clay, like that of Cheshire, much better adapted for permanent pasture than for the varied requirements of corn culture. Over the Lias and Oolite, consisting of alternations of calcareous and argillaceous strata, we have those noticeable belts of dry, rubbly, and stiff clayey soils, which

characterise a large portion of England, from Yorkshire on the north-east to Dorset and Somerset on the south-west-the calcareous freestones forming the drier ridges, and the clays the moister valleys.

In the south-east of England, the tracts coloured as Hastings sands, Weald Clay, Greensand, Gault, Chalk, and London Clay, are respectively characterised by thin, light sandy, stiff clayey, or dry calcareous soils-the direct results of the disintegration of their immediately underlying rocks. Indeed, this connection between the soils and subjacent rock-formations is best seen along the Secondary and Tertiary tracts of Englandthat is, from the New Red Sandstone upwards through the Lias, Oolite, Wealden, Chalk, and Eocene deposits of the London and Hampshire basins. No doubt sporadic patches of diluvial drifts occur here and there to break the connection, but, generally speaking, the soils, modes of culture, crops (wheat, barley, beans, hops), coincide with and are favoured by the lithological belts, as depicted on the geological maps of the country.

Nor do these lithological areas influence alone the white and green crops of the husbandman; they are equally, if not still more, operative in the growth and value of the timber trees of the forester. The firs and larches which thrive so magnificently on the decomposed mica-schists of the Scottish Highlands would be but poor stunted sticks on the thin cold clays of the granite; while the oaks, and elms, and orchardgrowths which flourish on the marly clays of the New Red Sandstone, would become stunted and gnarled if transferred to the drier and scantier soils of the Chalk and Carboniferous limestone.

Soils of Transport.

When we turn to the soils of transport we find them of a much more miscellaneous character, and occupying much more extensive and unbroken areas. Some consist of riverdrifts-shingly gravel, sand, or alluvium; others of old lakesites-peaty earth, clays, sands; some of old estuary bedstenacious clays and silts; others, again, of wind-blown sands and sand-dunes; and many of glacial drifts-sand, shingly gravels, and stiff bouldery clays. These may of themselves form the arable soils, or they may constitute the subsoils, and be overlaid by a coating of less or greater thickness, partly derived from their own disintegration, augmented by the growth and decay of plants, and partly formed by the plough and repeated cultivation. But whatever be their nature and

origin, they are little, if at all, influenced by the subjacent rock-formations, and have to be studied and treated by themselves. Over the Old Red Sandstone, the Carboniferous and Permian systems, which consist mainly of sandstones, shales, and clays, there is in most parts of the British Islands a thick coating of diluvial or bouldery clay, very stiff, retentive, and sterile. Much of this boulder-clay has been brought from a distance by ice-action; but the major portion, perhaps, is but the ground-up material of the formations on which it rests, hence its reddish tints on Old Red tracts, and its dark-blue colour over the Coal-formation. In many of our larger plains -Strathmore and Strathearn, for example-there is a very miscellaneous assortment of drifts-sands, gravels, shingly debris, and boulder-clays; and in the lower and wetter portions, peat-earths and alluvia, the remains of silted-up lakes, or of lakes still in process of obliteration. In our lower carses and valleys-Carses of Gowrie, Falkirk, and along the Humber -there are large expanses of soft plastic clays (old estuary bottoms) of great fertility, but of difficult and uncertain cultivation; while such tracts as the Fens of Lincoln, Romney Marsh, and the like, are chiefly marine silts and marsh growths. Sand-dunes, or link-lands along the sea-shores, and inland marshes, also occupy extensive tracts; and, indeed, by far the larger area of these islands consists of subsoils and surface soils, having no connection with the rocks on which they rest, and little, if at all, influenced by their proximity. These soils of transport must therefore be studied and treated by themselves, whether as regards fertile and permanent admixture, draining, or manuring.

Along with these soils of transport may be classed some of organic accumulations, such as peat-moss and bog-earths, which have no geological connection with the subsoils or rocks on which they repose. Such accumulations are often of great thickness, and rest on old estuary and lake silts, on sands, and on clays of totally different origin, and indeed, as in the case of Blair-Drummond, the peaty stratum may be altogether removed in order to expose the finer and more fertile clay that lies below.

Fertile Admixture of Soils.

It must be obvious that soils varying so much in their origin, composition, and texture cannot be all alike culturable and fertile; and hence to correct the one by admixture with the other, to render this one more friable and that more compact, to improve this one by drainage and that by manuring, is the sum and substance of judicious and successful farming.