SOIL. 



by time from the various earthy and other bodies in nature, 

 being ground down, and incorporated with each other in 

 different ftites and proportions, conllitute earthy layers, 

 which are ufually denominated foils, and which are deftined 

 to promote the growth and fupport oi various vegetable 

 crops : while the more folid and lefs reduced fubitances, 

 which have been excluded from the influence of the at- 

 mofphere, and other natural caufes, form the under llratum, 

 which is commonly known by the title of fub-foil. On 

 this account, it is evident that there mult be a great divcr- 

 fity in the foils of different diftritts. The more compadl 

 and hard fubftances of nature, the reduftion of which is 

 effected in a more flow and gradual manner, are generally 

 found more fparingly in the principles of foils, than thofe 

 of the more foft and eafily reducible kinds. But in the 

 natural Itate of foils, the clayey, loamy, and vegetable ma- 

 terials are generally found to enter in a pretty large pro- 

 portion, and to conilitute very eflential differences, according 

 to the quantities in which they are predominant in them. 

 And the earthy vegetable matter is, in many cafes, a prin- 

 cipal material in foils, conftituting a fort of fuperficial 

 layer or bed, in which the crops grow and are fupported ; 

 but which differs greatly according to the quantity, and 

 the itate of reduftion or decay to which it has advanced, 

 as well as many other circumttances. (See Vegetable 

 Earth.) Alfo, fubitances of the calcareous, fihceous, and 

 fandy kinds, are abundantly prevalent in fome trafts of 

 country, while in others they are met with only in a very 

 fparing manner, and thus of courfe afford much variety in 

 the nature and properties of the foils of fuch fituations. 

 Other caufes, which our limits will not allow us to mention 

 in this place, contribute to produce very great varieties and 

 diverfities in the natures and compofitions of foils. 



It has been well obferved by profeilor Davy, in an excel- 

 lent paper on the Analyfis of Soils, that the fubftances 

 which are found in foils, are certani mixtures or combina- 

 tions of fome of the primitive earths, animal and vegetable 

 matter in a decompofing itate, certain faline compounds, 

 and the oxyd of iron. Thefe bodies always retain water, 

 and exiit in very different proportions in different lands, 

 and the end of analytical experiments is the deteftion of 

 their quantities and mode of union. Bnt that the earths 

 found in common foils are principally filex, or the earths of 

 flints, alumina, or the pure matter of clay, lime, or cal- 

 careous earth and magncfia. That filex, or filica, or the 

 earth of flints, when pcrfetlly pure, appears in the form of 

 a white powder, which is incombuftible, infufible, infoluble 

 in water, and not afted upon by common acids ; it is the 

 fubftance which conflitutes the principal part of rock cryf- 

 tal ; it compofes a confiderable part of hard gravelly foils, 

 of hard fandy foils, and of hard ftony lands. 



That alumine, alumina, or pure clay, in its perfeft flate 

 i« white, like filex ; it adheres ftrongly to the tongue, is in- 

 combuitible, infoluble in water, but foluble in acids, and 

 in fixed alkaline menftrua. It abounds molt in clayey loils 

 and clayey loams ; but even in the fmalleft particles of thefe 

 foils, it is ufually united to filex and oxyd of iron. 



That lime is the fubftance, which is well known in its 

 pure (late under the name of quicklime. It always cxifts 

 in foils in combination, and that principally with fixed air 

 or carbonic acid, when it is called carbonate of hmc ; a fub- 

 ftance which, in the moll compatt form, conllitiites marble, 

 and in its loofer form, chalk. Lime, when combined with 

 (ulphuric acid (oil of vitriol), produces fulphate of Hme 

 (gypfum), and with phofphoric acid, phofphate of Hme. 

 The carbonate of hme, mixed with other fubftances, com- 



pofes chalky foils and marles, and is found in foft fandy 

 foils. 



That magnefia, when pure, appears as white, and in a 

 lighter powder than any of the other earths ; it is foluble 

 in acid, but not in alkaHne menftrua ; it is rarely found in 

 foils ; when it does exift, it is either in combination with 

 carbonic acid, or with filex and alumine. 



That animal decompofing matter exifts in very different 

 ftates, according as the fubftances from which it is produced 

 are different ; it contains much carbonaceous fubftance, and 

 may be principally refolved by heat into this fubftance, 

 volatile alkali, inflammable aeriform produAs, and carbonic 

 acid ; it is principally found in lands that have been lately 

 manured. 



That vegetable decompofing matter is likewife very va- 

 rious ill its kind ; it contains ufually more carbonaceous fub- 

 ftance than animal matter, and differs from it in the refults 

 of its decompofition, principally in not producing volatile 

 alkali ; it forms a great proportion of all peats ; it abounds 

 in rich mould ; and is found in larger or fraaller quantities in 

 all lands. 



That the faline compounds found in foils are very few, 

 and in quantities fo fmall that they are rarely to be difcovered. 

 They are principally muriate of foda (common fait), ful- 

 phate of magnefia (Epfora fait), and muriate and fulphate 

 of potafh, nitrate of lime, and the mild alkalies. 



That the oxyd of iron is the fame with the ruft produced 

 by expofing iron to the aftion of air and water ; it is found 

 in all foils, but is more abundant in yellow and red clays, 

 and in yellow and red filiceous fands. 



There is, befides thefe, fometimes sxyd of manganefum, or 

 manganefe, found in foils, which is compofed of this fub- 

 ftance and oxygen. It is known from other matters met 

 with in foils, by the property which it has of decompofing 

 muriatic acid, and converting it into another fubftance. 



The filex, or filica, is for the moft part met with in foiU 

 in the ftate of combination with alumine, or alumina, and the 

 oxyd of iron, or with the former, lime, magncfia, and oxyd 

 of iron, conftituting fand and gravel of very different degree* 

 of finenefs, as well as varying much in colour. The carbo- 

 nate of lime is commonly found in an impalpable form ; but 

 occafionally in the ftate of calcareous fand. The magnefia, 

 when not combined with the gravel or fand of the foil, is in 

 general united in a fine powdery flate to carbonic acid. The 

 fine impalpable parts of foil, which are moft commonly de- 

 nominated clay or loam, confifl, as has been fcen, of filex 

 or filica, alumine or alumina, lime, and magnefia ; and arc 

 in reality, for the moft part, of the fame compofition as the 

 hard fand, but more finely divided in their particles. As to 

 the vegetable and animal matters of foils, the former of 

 which is by much the moft common, they exifl in many very 

 different ftates of redudljon and decompofition, as fometimes 

 in that of a quite fibrous one, and at other times they are 

 wholly broken down, and reduced fo as to be intimately 

 blended and incorporated with the earthy p.irts of the foils 

 or lands. 



The matters therefore which conftitute foils are for the 

 moft part of a compound nature, and operate as fuch in the 

 formation of them. They have many of them, likewife, 

 fome other qualities and properties, but which need not be 

 noticed in this place. 



It has alfo been flated by a late praftical writer, that there 

 are probably few, if any, fubftances in nature, which, after 

 they have been fufiiciently afted upon, and reduced by the 

 influence of the atmolphcre and other agents, that are not 

 capable of ailording lupport to feme kind of vegetable or 

 K k a other, 



