BOOK II. ALTERATION OF THE PARTS OF SOILS. 229 



SUBSECT. 4. Alteration of the constituent Parts of Soils. 



1083. The constituent parts of soils may be altered by the addition or subtraction of in- 

 gredients in which they are deficient, or superabound, and by the chemical changes of 

 some constituent part or parts by the action of fire. 



1084. In ascertaining the composition of faulty soils with a view to their improvement 

 by adding to their constituent parts, any particular ingredient which is the cause of their 

 unproductiveness, should be particularly attended to ; if possible, they should be com- 

 pared with fertile soils in the same neighbourhood, and in similar situations, as the dif- 

 ference of the composition may, in many cases, indicate the most proper methods of im- 

 provement. If, on washing a sterile soil, it is found to contain the salts of iron, or any 

 acid matter, it may be ameliorated by the application of quick-lime. A soil of good ap- 

 parent texture, containing sulphate of iron, will be sterile ; but the obvious remedy is a 

 top-dressing with lime, which converts the sulphate into manure. If there be an excess 

 of calcareous matter in the soil, it may be improved by the application of sand or clay. 

 Soils too abundant in sand are benefited by the use of clay, or marl, or vegetable matter. 

 Light sands are often benefited by a dressing of peat, and peats by a dressing of sand ; 

 though the former is in its nature but a temporary improvement. When peats are acid, 

 or contain ferruginous salts, calcareous matter is absolutely necessary in bringing them 

 into cultivation. The best natural soils are those of which the materials have been de- 

 rived from different strata, which have been minutely divided by air and water, and are 

 intimately blended together ; and in improving soils artificially, the cultivator cannot do 

 better than imitate the processes of nature. The materials necessary for the purpose are 

 seldom far distant ; coarse sand is often found immediately on chalk, and beds of sand 

 and gravel are common below clay. The labor of improving the texture or constitution 

 of the soil, is repaid by a great permanent advantage, less manure is required, and its 

 fertility insured ; and capital laid out in this way secures for ever the productiveness, and 

 consequently the value of the land. 



1085. The removal of superabundant ingredients in soils may sometimes be one of the 

 simplest and most effectual means of their improvement. It occasionally happens that 

 the surface of a well proportioned soil is thickly covered with peat, with drifted sand, 

 with gravel, or with small stones. Extensive examples of the former occur in Stirling- 

 shire, and of the latter in Norfolk. In such cases, a simple and effectual mode of im- 

 provement consists in removing the superincumbent strata, and cultivating that below. 

 This can seldom be put in practice on a large scale, with such heavy materials as gravel 

 or stones ; but some hundreds of acres of rich alluvial soil, deeply covered by peat, have 

 been bared and cultivated in Flanders moss in Stirlingshire ; an operation commenced by 

 the celebrated Lord Kaimes, (Gen. Rep. of Scot. App. v. 5.) copied by his neighbours, 

 and continued by his and their successors. The moss is floated off by streams of water, 

 which empty themselves in the Frith of Forth. In this river, by the winds and tides, it 

 is cast on shore in the bays and recesses, impregnated with salt ; and here it ingenders 

 vegetation on the encroaching surfaces of sand and gravel. Coatings of sand or gravel 

 can seldom be removed on a scale of sufficient extent for agriculture, but have, in some 

 instances, for the purposes of gardening. Sometimes this improvement may be effected 

 by trenching down the surface, and raising up a stratum of better earth. 



1086. Incineration. The chemical changes which can be effected in soils by inciner- 

 ation are considerable. This practice was known to the Romans, is more or less in use 

 in most parts of Europe, is mentioned as an approved practice by our oldest agricultural 

 writers, and has lately excited some degree of attention from the successful experiments 

 of different cultivators. (Farmer's Magazine, 1810 to 1815, and Farmers' Journal, 

 1814 to 1821.) 



1087. The theory of burning soils is thus given by Sir H. Davy. It rests, he says, 

 entirely on chemical doctrines. The bases of all common soils, are mixtures of the 

 primitive earths and oxide of iron ; and these earths have a certain degree of attraction for 

 each other. To regard this attraction in its proper point of view, it is only necessary to 

 consider the composition of any common siliceous stone. Feldspar, for instance, contains 

 siliceous, aluminous, calcareous earths, fixed alkali, and oxide of iron, which exist in one 

 compound, in consequence of their chemical attractions for each other. Let this stone be 

 ground into impalpable powder, it then becomes a substance like clay . if the powder be 

 heated very strongly, it fuses, and on cooling forms a coherent mass similar to the original 

 stone ; the parts separated by mechanical division adhere again in consequence of chemical 

 attraction. If the powder is heated less strongly, the particles only superficially combine 

 with each other, and form a gritty mass, which, when broken into pieces, has the characters 

 of sand. If the power of the powdered feldspar to absorb water from the atmosphere 

 before, and after the application of the heat, be compared, it is found much less in the 

 last case. The same effect takes place when the powder of other siliceous or aluminous 



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