COMPOSITION OF SOILS AJND THEIR ACTION. 47 



Silicious gravel . 32 parts. | Carbonate of Lime 19 parts. 

 Calcareous gravel II " | Alumina . . 21 " 

 Silica . . . 10 " I Vegetable remains 7 " 



A specimen of soil from Touraine, celebrated for 

 the production of hemp, gave of 



Coarse gravel . 49 parts. I Silica . . 17 parts. 



Carbonate of Lime 25 '* ' Alumina . . 16 " 



In nearly all cultivated soils in good tilth, the 

 quantity of animal and vegetable matter is nearly 

 the same, or about one tenth of the whole. These 

 examples, and a great number of examinations of 

 soil by Davy, Bergmann, and Chaptal, show about 

 the same result, and exhibit conclusively the propor- 

 tions in which these three principal earths, lime, clay, 

 anfl sand, should be mixed, in order to produce the 

 best soils for cultivation. Where this is well under- 

 stood, a following out of the principles here laid 

 down in bringing the soil, by a proper mixture of 

 these earths, to a right proportion, will ensure a qual- 

 ity of soil of the best and most valuable kind. If 

 either of these earths exist in too great proportions, 

 the land will be comparatively poor, and its power 

 of vegetation diminished. 



For instance, if land is found to contain too much 

 calcareous matter (a very rare fault, however, by- 

 the-way), the difficulty is to be remedied most ef- 

 fectually by an application of argillaceous or clayey 

 marl, a substance principally composed of clay and 

 sand. Land which contains too much silex will be 

 benefited by the application of calcareous marl, or 

 marl composed of lime, clay, and sand ; while soils 

 in which clay predominates need the addition of 

 sand and gravel ; if calcareous gravel or sand, so 

 much the better. In soils where but one of these 

 earths is present, there can be little or no vegetation, 

 and their fertility increases exactly in proportion to 

 their proper mixture. 



In an arable soil it is necessary, whatever may be 

 its constituents, that it should not be too fine. In 



