Book 11. 



CLASSIFICATION OF SOILS. 



219 



are found in the outskirts of them, bear the marks of having been felled. In theinterior, few entire trees 

 are found ; and the cause is, probably, that thev fell by gradual decay ; and that the fermentation and 

 decomposition of tlie vegetable matter was the most rapid where it was 'in the greatest (juantity. 



1027. 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 difierent kind. Much more gaseous matter is evolved ; and the 

 neighbourhood of morasses, in which aquatic vegetables decompose, is usually aguish and unhealthy j 

 whilst that of the true peat, or peat formed on soils originally dry, is ahvays salubrious. 



10^8. Soils rncy gemralli/ be distinguished from mere masses of eartlih^ \.\\€\x 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, iniless in crevices, where they had been washed in by 

 rains ; and in cultivated soils their depth is generallv the same as that to which the implements used in 

 cultivation have penetrated. 



1029. ^luch 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 dis- 

 courses on soils were published by Bacon, Evelyn, Bradley and others ; but itmay 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. One reason for this failure is, that some of the principal efTects of operations on soils are chemical, 

 and chemistry, till within the last forty years, could hardly be considered an inductive science. In so little 

 esteem was it held in Evelyn's time, that he ranks it with astrology, and considers the term as synonymous 

 with alchemy. [Ten-a, p. -i. ai^id ^ie^?!oirs, Sec. i.) Jethro Tull, about 60 years after the publication of 

 Evelyn's Terra, published a system of culture, in which every thing was referred to mechanical division ; 

 but though he referred to this theory the beiieficial influence of some excellent practices, yet neither 

 gained ground at the time The first attempt to treat of soils chemically, was made by Kirwan about 

 ITSt), the next by Lord Dundonald in 1795, and then followetl Dr. Darwin's Pliytologia in ISUO, and 

 lastly. Sir H. Davy's Lectures on Agricultural Chemistry in 1S02. It is from the last edition (in 1821) 

 of that valuable work, that we shall chiefly make our selections. 



Sect.il Classification and Nomenclature of Soils. 



1030. Systematic order and an agreed nomenclature are as necessary in the study of soils 

 as of plants or animals. The number of provincial terms for soils Avhich have found 

 their way into the books on cultivation, is one reason why so little use can be made of 

 their directions. 



103L 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. 

 priinitive 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 car- 

 bonic matter. Tlie orders may be subdivided into genera founded on the prevailing 

 earths, salts, metals, or carbon ; the genera into species founded on their different mix- 

 tures ; the species into varieties founded on color, texture ; and sub-varieties founded on 

 moisture, dryness, richness, lightness, Sec. 



1032. In naniing the genera of soils, the first tiling 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 tliem from those that are siliceous. The term clayey soil 

 should not be applied to any laqd which contains less than one sixth of impalpable 

 eartliy 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 

 witli 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 de- 

 composed matter of one particular rock, a name derived from the rock may with pro- 

 priety be applied to it. Thus, if a fine red earth be found immediately above decom- 

 posing basalt, it may be denominated basaltic soil. If fragments of quartz and mica be 

 found abundant in the materials of t!ie soil, which is often the case, it may be 

 denominated granitic soil; and the same principles may be applied to other like instances. 

 In genera], the soils, the materials of which are the most various and heterogeneous, are 

 those called alluvial, or wliich 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. 



1033. In na7ning 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 tlie color or texture of that mixture which belongs to the nomenclature of varieties. 

 I'hus 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 expresses at once the genus, species, and variety. A soil con- 



