End, in Cornwall. The rocks and earths presented in this line are, the Windsor alluvion (2), Hampshire and Salisbury chalk (3), alluvion (4), sandstone (5), alluvion (6), Sherborne freestone (7), sandstone (8), 245

10

blue lias limestone (9), Blackdown sandstone (10), Devonshire red sandstone (11), mountain limestone (12), Dartmoor slate (13), granite (14), slate again (15), greenstone (16), Cornwall serpentine (17), slate killas (18), Cornwall granite (19), slate killas (20), and finally Cornwall granite.

2058. The second section (fig. 246.) commences with the coal strata, and limestone resting upon slate 246

and granite in Cumberland, and thence proceeds towards the metropolis by Yorkshire, Derbyshire, Leicestershire, Northamptonshire, Bedfordshire, and Hertfordshire. The passage is here exhibited from the primary rocks of Cumberland to the secondary hills of the southern counties. It shows the Cumberland coal (a), limestone and slate (b), the Mossdale granite (c), slate (d), grauwacke (e), Ribblesdale limestone (f), gritstone (g), Ashton coal (h), Derby limestone (2), Derby toadstone (k), gritstone (4), gypsum (m), sandstone (n), limestone (0), Charnwood slate (p), Mountsorrel granite (q), red sandstone (7), lias limestone (s), Northampton oolite or freestone (1), Woburn sand (u), Dunstable chalk (v), and terminates in the London clay (w), with which the first section sets out.

2059. The surface earth, or that which forms the outer coating of the dry parts of the globe, is formed by the detritus, or worn off parts of rocks and rocky substances. For in some places, as in chasms and vacuities between rocky layers or masses, earth occupies many feet in depth, and in others, as on the summits of chalk hills or granite mountains, it hardly covers the surface.

2060. Earths are therefore variously composed, according to the rocks or strata which have supplied their particles. Sometimes they are chiefly formed from slate-rocks, as in blue clays; at other times from sandstone, as in siliceous soils; and mostly of a mixture of clayey, slatey, and limestone rocks, blended in proportions as various as their situations. Such we may suppose to have been the state of the surface of the dry part of the globe immediately after the last disruption of its crust; but in process of time the decay of vegetables and animals form additions to the outer surface of the earths, and constitute what are called soils; the difference between which and earths is, that the former always contain a portion of vegetable or animal matter.

2061. The manner in which rocks are converted into soils, Sir H. Davy observes (Elem. of Agric. Chem. 188.), may be easily conceived by referring to the instance of soft granite, or porcelain granite. This substance consists of three ingredients, quartz, feldspar, and mica. The quartz is almost pure siliceous earth in a crystalline form. The feldspar and mica are very compounded substances; both contain silica, alumina, and oxide of iron; in the feldspar there is usually lime and potassa; in the mica, lime and magnesia. When a granite rock of this kind has been long exposed to the influence of air and water, the lime and the potassa contained in its constituent parts are acted upon by water or carbonic acid; and the oxide of iron, which is almost always in its least oxidised state, tends to combine with more oxygen; the consequence is, that the feldspar decomposes, and likewise the mica; but the first the most rapidly. The feldspar, which is as it were the cement of the stone, forms a fine clay: the mica, partially decomposed, mixes with it as sand; and the undecomposed quartz appears as gravel, or sand of different degrees of fineness. As soon as the smallest layer of earth is formed on the surface of a rock, the seeds of lichens, mosses, and other imperfect vegetables which are constantly floating in the atmosphere, and which have made it their resting-place, begin to vegetate; their death, decomposition, and decay afford a certain quantity of organisable matter, which mixes with the earthy materials of the rock; in this improved soil more perfect plants are capable of subsisting; these in their turn absorb nourishment from water and the atmosphere; and, after perishing, afford new materials to those already provided: the decomposition of the rock still continues; and at length, by such slow and gradual processes, a soil is formed in which even forest-trees can fix their roots, and which is fitted to reward the labors of the cultivator.

2062. The formation of peaty soils is produced from very opposite causes, and it is interesting to contemplate how the same effect may be produced by different means, and the earth which supplies almost all our wants may become barren alike from the excessive application of art, or the utter neglect of it. Continual pulverisation and cropping, without manuring, will certainly produce a hungry barren soil; and the total neglect of fertile tracts will, from their accumulated vegetable products, produce peat soils and bogs. Where successive generations of vegetables have grown upon a soil, Sir H. Davy observes, unless part of their produce has been carried off by man, or consumed by animals, the vegetable matter increases in such a proportion, that the soil approaches to a peat in its nature: and if in a situation where it can receive water from a higher district, it becomes spongy and permeated with that fluid, and is generally rendered incapable of supporting the nobler classes of vegetables.

2063. Spurious peaty soil. Lakes and pools of water are sometimes filled up by the accumulation of the remains of aquatic plants; and in this case a sort of spurious peat is formed. The fermentation in these cases, however, seems to be of a different kind. Much more gaseous matter is evolved; and the neighborhood of morasses, in which aquatic vegetables decompose, is usually aguish and unhealthy; whilst that of the true peat, or peat formed on soils originally dry, is always salubrious.

2064. Soils may generally be distinguished from mere masses of earth by their friable texture, dark color, and by the presence of some vegetable fibre or carbonaceous matter. In uncultivated grounds, soils occupy only a few inches in depth on the surface, unless in crevices, where they have been washed in by rains; and in cultivated soils their depth is generally the same as that to which the implements used in cultivation have penetrated.

2065. Much has been written on soils, and till lately, to very little purpose. All the Roman authors on husbandry treated the subject at length; and in modern times, in this country, copious philosophical discourses on soils were published by Bacon, Evelyn, Bradley, and others; but it may be truly said, that in no department of cultivation was ever so much written of which so little use could be made by practical men.

SECT. II. Classification and Nomenclature of Soils.

2066. Systematic order and an agreed nomencluture are as necessary in the study of soils as of plants or animals. The number of provincial terms for soils which have found their way into the books on cultivation, is one reason why so little use can be made of their directions.

2067. A correct classification of soils may be founded on the presence or absence of organic and inorganic matter in their basis. This will form two grand classes, viz. primitive soils, or those composed entirely of inorganic matter, and secondary soils, or those composed of organic and inorganic matter in mixtures. These classes may be

subdivided into orders founded on the presence or absence of saline, metallic, and carbonic matter. The orders may be subdivided into genera founded on the prevailing earths, salts, metals, or carbon; the genera into species founded on their different mixtures; the species into varieties founded on color, or texture; and sub-varieties founded on moisture, dryness, richness, lightness, &c.

2068. In naming the genera of soils, the first thing is to discover the prevailing earth or earths; either the simple earths, as clay, lime, sand, or the particular rocks from which the soil has been produced, as granite, basalt, &c. When one earth prevails, the generic name should be taken from that earth, as clayey soil, calcareous soil, &c.; when two prevail to all appearance equally, then their names must be conjoined in naming the genus, as clay and sand, lime and clay, basalt and sand, &c. The great thing is precision in applying the terms. Thus, as Sir H. Davy has observed, the term sandy soil should never be applied to any soil that does not contain at least seven eighths of sand; sandy soils that effervesce with acids should be distinguished by the name of calcareous sandy soil, to distinguish them from those that are siliceous. The term clayey soil should not be applied to any land which contains less than one sixth of impalpable earthy matter, not considerably effervescing with acids; the word loam should be limited to soils, containing at least one third of impalpable earthy matter, copiously effervescing with acids. A soil to be considered as peaty, ought to contain at least one half of vegetable matter. In cases where the earthy part of a soil evidently consists of the decomposed matter of one particular rock, a name derived from the rock may with propriety be applied to it. Thus, if a fine red earth be found immediately above decomposing basalt, it may be denominated basaltic soil. If fragments of quartz and mica be found abundant in the materials of the soil, which is often the case, it may be denominated granitic soil; and the same principles may be applied to other like instances. In general, the soils, the materials of which are the most various and heterogeneous, are those called alluvial, or which have been formed from the depositions of rivers; and these deposits may be designated as siliceous, calcareous, or argillaceous; and in some cases the term saline may be added as a specific distinction, applicable, for example, at the embouchure of rivers, where their alluvial remains are overflown by the sea.

2069. In naming the species of soils, greater nicety is required to determine distinctions than in naming the genera; and there is also some difficulty in applying or devising proper terms. The species are always determined by the mixture of matters, and never by the color or texture of that mixture which belongs to the nomenclature of varieties. Thus a clayey soil with sand is a sandy clay, this is the name of the species; if the mass is yellow, and it is thought worth while to notice that circumstance, then it is a yellow sandy clay, which express at once the genus, species, and variety. A soil containing equal parts of clay, lime, and sand, would, as a generic term, be called clay, lime, and sand; if it contained no other mixture in considerable quantity, the term entire, might be added as a specific distinction; and if notice was to be taken of its color or degree of comminution, it might be termed a brown, a fine, a coarse, a stiff, or a free entire clay, lime, and sand.

2070. The following Table enumerates the more common genera, species, and varieties of soils. The application of the terms will be understood by every cultivator, though to attempt to describe the soils either chemically, or empirically (as by sight, smell, or touch), would be a useless waste of time. From a very little experience in the field or garden, more may be gained in the study of soils, than from a volume of such descriptions. This table corresponds with the nomenclature adopted in the agricultural establishments of Fellenberg at Hofwyl in Switzerland, of Professor Thaer at Moegelin in Prussia, of Professor Thouin in his lectures at Paris, and in general with that of all the continental professors. It is therefore very desirable that it should become as generally adopted as that of the Linnæan system in botany. The principle of the table may be extended so as to include any other soil whatever.

2071. The value of soils to the cultivator, is discoverable botanically, chemically, and mechanically; that is, by the plants that grow on them naturally; by chemical analysis; and by exterior and interior inspection of handling.

SUBSECT. 1. Of discovering the Qualities of Soils by means of the Plants which grow

on them.

2072. Plants are the most certain indicators of the nature of a soil; for while no practical cultivator would engage with land of which he knew only the results of a chemical analysis, or examined by the sight and touch a few bushels which were brought to him, yet every gardener or farmer, who knew the sort of plants it produced, would be at once able to decide as to its value for cultivation.

2073. The leading soils for the cultivator are the clayey, calcareous, sandy, ferrugineous, peaty, saline, moist or aquatic, and dry. The following are the plants by which such soils are distinguished in most parts of Europe:

2074. Argillaceous. Tussilago farfara, Potentilla anserina, argentea, and reptans. Thalictrum flavum, Carex, many species. Juncus, various species. Orobus tuberosus,

Lotus major, and corniculatus. Saponaria officinalis. But the Tussilago farfara is a certain and universal sign of an argillaceous soil, and is the chief plant found on the alum grounds of Britain, France, and Italy.

2075. Calcareous. Veronica spicata, Gallium pusillum, Lithospermum officinale, and purpuro-cæruleum. Campanula glomerata, and hybrida. Phyteuma orbicularis, Verbascum lychnitis, Viburnum lantana, Berberis vulgaris, Cistus helianthemum, Anemone pulsatilla, Clematis vita alba, Hedysarum onobrychis.

2076. Siliceous. Veronica triphyllus, and verna. Echium italicum, Hernaria glabra, and hirsuta. Silene anglica and other species. Arenaria rubra, &c. Spergula arvensis, Papaver hybridum, Argemone, &c.

2077. Ferrugineous. Rumex acetosa, and acetosella.

2078. Peaty. Vaccinium myrtillus, uliginosum, and oxycoccus. Erica 4 sp. Spergula subulata. Tormentilla officinalis.

2079. Saline. Salicornea 4 species. Zostera marina, Ruppia maritima, Pulmonaria maritima, Convolvulus soldanella, Illecebrum verticillatum, Chenopodium maritimum, Salsola kali, and fruticosa. Sium verticillatum. Arenaria maritima, &c. Atriplex laciniata.

2080. Aquatic. Caltha palustris, Hippuris vulgaris. Pinguicula vulgaris, Lycopus europeus, Valeriana dioica, Viola palustris, Samolus valerandi, Silenum palustre, Epilobium tetragonum, Lythrum salicaria, Ranunculus lingula, and flamula.

2081. Very dry. Arenaria rubra, Rumex acetosella, Thymus Serpyllum, Acinos vulgaris, Trifolium arvense.

2082. These plants are not absolutely to be depended on, however, even in Britain; and in other countries they are sometimes found in soils directly opposite. Still, the saintfoin is almost always an indication of a calcareous soil; the common coltsfoot (Tussilago farfara), of blue clay; the arenaria rubra, of poor sand; the small woodsorrel of the presence of iron, or of peat. The common reed-grass (Arundo phragmites), and the common pond weed (Polygonum amphibium), grow on alluvial soils, which yield excellent crops if properly drained; but where the field horse-tail (Equisetum arvense) grows freely, it indicates a cold and retentive subsoil. The field pimpernell (Anagallis arvensis), the field madder (Sherardia arvensis), the corn gromwell (Lithospermum arvense), and the lamb's lettuce (Fedia olitoria), grow on cultivated lands, where the soil is a strong black loam on a dry bottom; when such a soil is wet, the clown's all-heal (Stachys. palustris) makes its appearance. A light sandy soil is known by the presence of the red dead nettle (Lamium purpureum); the shepherd's purse (Thlaspi bursa pastoris). If the parsley piert (Aphanes arvensis) is found, the soil is rather unproductive; if the corn spurry (Spergula arvensis) grows very thick, the ground has likely been rendered too fine by the harrow; the common ragwort (Senecio Jacobea), and the corn thistle (Serratula arvensis), grow indiscriminately on light and strong loams, but always indicate a fertile soil. The whitlow grass (Draba muralis), and the common knawel (Scleranthus annuus), grow on soils that are dry, sandy, and poor in the extreme. The common rest harrow (Ononis hircina) is often found on dry pasture, and where the soil is incumbent on rotten rock. The aquatic, peaty, and saline soils are almost every where indicated by their appropriate plants; a proof, as we have before stated, that the climate and natural irrigation of plants have much more influence on their habits than mere soil. (See the Stationes Plantarum of Lin. and the Flora Française of De Candolle; Galpine's Compendium, Flora Brit.; Smith's Flora Brit.; Kent's Hints; and Farmers' Mag. Feb. 1819.)

It is not

SUBSECT. 2. Of discovering the Qualities of Soils by Chemical Analysis. 2083. Chemical analysis is much too nice an operation for general purposes. likely that many practical cultivators will ever be able to conduct the analytic process with sufficient accuracy, to enable them to depend on the result. But still such a knowledge of chemistry as shall enable the cultivator to understand the nature of the process and its results, when made and presented to him by others, is calculated to be highly useful, and ought to be acquired by every man whose object is to join theoretical to practical knowledge. If it so happens that he can perform the operations of analysis himself, so much the better, as far as that point is concerned; but on the whole, such knowledge and adroitness is not to be expected from men who have so many other points demanding their attention, and who will, therefore, effect their purpose much better by collecting proper specimens of the soils to be studied, and sending them for analysis to a respectable operative chemist.

2084. In selecting specimens, where the general nature of the soil of a field is to be ascertained, portions of it should be taken from different places, two or three inches below the surface, and examined as to the similarity of their properties. It sometimes happens, that upon plains, the whole of the upper stratum of the land is of the same kind, and in this case, one analysis will be sufficient; but in valleys, and near the beds of rivers, there are very great differences, and it now and then occurs that one part of a field is calcareous,

and another part siliceous; and in this case, and in analogous cases, the portions different from each other should be separately submitted to experiment. Soils, when collected, if they cannot be immediately examined, should be preserved in phials quite filled with them, and closed with ground glass stoppers. The quantity of soil most convenient for a perfect analysis is from two to four hundred grains. It should be collected in dry weather, and exposed to the atmosphere till it becomes dry to the touch.

2085. The soil best suited for culture, according to the analysis of Bergman, contains four parts of clay, three of sand, two of calcareous earth, and one of magnesia; and, according to the analysis of Fourcroy and Hassenfratz, 9216 parts of fertile soil contained 305 parts of carbon, together with 279 parts of oil; of which, according to the calculations of Lavoisier, 220 parts may be regarded as carbon so that the whole of the carbon contained in the soil in question may be estimated at about 525 parts, exclusive of the roots of vegetables, or to about one sixteenth of its weight. Young observed that equal weights of different soils, when dried and reduced to powder, yielded by distillation quantities of air somewhat corresponding to the ratio of their values. The air was a mixture of fixed and inflammable airs, proceeding probably from decomposition of the water; but, partly, it may be presumed, from its capacity of abstracting a portion of air from the atmosphere, which the soil at least is capable of doing. The following is the analysis of a fertile soil, as occurring in the neighborhood of Bristol: In 400 grains, there were of water, 52; siliceous sand, 240; vegetable fibre, 5; vegetable extract, 3; alumine, 48; magnesia, 2; oxide of iron, 14; calcareous earth, 30; loss, 6. But Kirwan has shown in his Geological Essays, that the fertility of a soil depends in a great measure upon its capacity for retaining water; and if so, soils containing the same ingredients must be also equally fertile, all other circumstances being the same; though it is plain that their actual fertility will depend ultimately upon the quantity of rain that falls, because the quantity suited to a wet soil cannot be the same that is suited to a dry soil. And hence it often happens that the ingredients of the soil do not correspond to the character of the climate. Silica exists in the soil under the modification of sand, and alumine under the modification of clay. But the one or the other is often to be met with in excess or defect. Soils in which the sand preponderates retain the least moisture; and soils in which the clay preponderates retain the most: the former are dry soils, the latter are wet soils. But it may happen that neither of them is sufficiently favorable to culture; in which case, their peculiar defect or excess must be supplied or retrenched before they can be brought to a state of fertility.

2086. Use of the result of analysis. In the present state of chemical science, Dr. Ure observes, no certain system can be devised for the improvement of lands, independently of experiment; but there are few cases in which the labor of analytical trials will not be amply repaid by the certainty with which they denote the best methods of melioration; and this will particularly happen, when the defect of composition is found in the proportions of the primitive earths. In supplying organic matter, a temporary food only is provided for plants, which is in all cases exhausted by means of a certain number of crops; but when a soil is rendered of the best possible constitution and texture, with regard to its earthy parts, its fertility may be considered as permanently established. It becomes capable of attracting a very large portion of vegetable nourishment from the atmosphere, and of producing its crops with comparatively little labor and expense. (Dict. of Chem. art. Soil.)

SUBSECT. 3. Of discovering the Qualities of a Soil mechanically and empirically. 2087. The physical properties of soils, and some of their most important constituents relatively to the cultivator, may be ascertained to a certain extent by various and very simple means.

2088. The specific gravity of a soil, or the relation of its weight to that of water, may be ascertained by introducing into a phial, which will contain a known quantity of water, equal volumes of water and of soil, and this may be easily done by pouring in water till it is half full, and then adding the soil till the fluid rises to the mouth; the difference between the weight of the soil and that of the water will give the result. Thus if the bottle contains four hundred grains of water, and gains two hundred grains when half filled with water and half with soil, the specific gravity of the soil will be 2, that is, it will be twice as heavy as water, and if it gained one hundred and sixty-five grains, its specific gravity would be 1825, water being 1000.

2089. The presence of clay and sand in any soil is known, the first by its tenacity, the other by its roughness to the touch, and by scratching glass when rubbed on it.

2090. The presence of calcareous matter in soil may be ascertained by simply pouring any acid on it, and observing if it effervesces freely. Calcareous soils are also softer to the touch than any other.