CALCAREOUS MANURES— THEORY, j^ 



and therefore are of much greater depth. Below the soil is the sub-soil, 

 which is also a mixture of two or more earths, but usually is almost as 

 barren as each of the unmixed or pure earths, because it contains very 

 little putrescent matter, the only food for plants. 



The qualities and value of soils depend on the proportions of their in- 

 gredients. We can easily comprehend in what manner silicious and 

 aluminous earths, by their mixture, serve to cure the defects of each other ; 

 the open, loose, thirsty, and hot nature of sand being corrected by, and 

 correcting in turn, the close, adhesive, and water-holding qualities of alumi- 

 nous earth. This curative operation is merely mechanical ; and in that 

 manner it seems likely that calcareous earth, when in large proportions, 

 also acts, and aids the corrective powers of both the other earths. This, how- 

 ever, is only supposition, as I have met with scarcely any such natural soil. 



But besides the mechanical effects of calcareous earth, (which perhaps 

 are weaker than those of the other two,) that earth has chemical powers far 

 more effectual in altering the texture of soils, and for which a compara- 

 tively small quantity is amply sufficient. The chemical action of calcareous 

 earth, as an ingredient of soils, will be fully treated of hereafter; it is only 

 mentioned in this place to avoid the apparent contradiction which might be 

 inferred, if, in a general description of calcareous earth, I had omitted all 

 allusion to qualities that will afterwards be brought forward as all-important. 



Nothing is more wanting in the science of agriculture, than a correct 

 nomenclature of soils, by which the characters might be learned from the 

 names; and nothing has hitherto seemed less attainable. The modes of 

 classing and naming soils, used by scientific authors, are not only different, 

 and opposed to each other, but each one of them is quite unfit to serve the 

 purpose intended. As to the crowd of inferior writers, it is enough to say 

 that their terms are not fixed by any rule, convey no precise meaning, and 

 are worth not much more than those in common use among ourselves, and 

 other practical cultivators, which often vary in their meaning within forty- 

 miles of distance. To enable us to judge of the fitness of the names given 

 to soils by others, let us examine those applied by ourselves. We gene- 

 rally describe soils by making a mental comparison with those we are most 

 accustomed to ; and though such a description is understood well enough 

 through a particular district, it may have quite a different meaning else- 

 where. What are called claij or stiff soils, in Sussex and Southampton, 

 would be considered sandy or light soils in Goochland— merely because al- 

 most ev'ery acre of land in the former counties is sandy, and in the latter, 

 clays are nearly as abundant. 



The conflict of definitions, and consequent confusion of terms, cannot be 

 more plainly set forth, than by quoting from some of the highest authorities, 

 the various and contradictory explanations of a term, loam, which is so 

 common that it is used by every one who writes or speaks of soils — and 

 which, in some one or other sense, each writer probably considered as form- 

 ing a very large, if not the greatest proportion of the cultivated soils of his 

 country, and of the world. 



" Loam denotes any soil moderately cohesive, and more so than loose 

 chalk. By the author of the Body of Agriculture, it is said to be a clay 

 mixed with sand.''' {Kirivan on 3Ia72ures — chap. 1.] 



" Loam, or that species of artificial soil into which the others are gene- 

 ally brought by the course of long cultivation."—" Where a soil is mode- 

 rately cohesive, less tenacious than clay, and more so than sand, it is known 

 by the name of loam. . From its frequency, there is reason to suppose that 

 in some cases it might be called an " original soil." [^Sinclair's Code of 

 Agricultvre—chap, 1.] 



