105 



OBSERVATIONS ON THE NATURE OF SOILS. 



As vegetables are in a great measure dependent upon the inorganic matter 

 by which they are surrounded, for their nourishment, and even for their exist- 

 ence, it is evident that our success in cultivation must be very materially influ- 

 enced by our knowledge of the physical condition and chemical composition of 

 the external elements, the laws which regulate their changes, and the means 

 we possess of modifying them. It may be safely asserted, that all the principles 

 which have been ascertained as entering into the process of vegetation, are fur- 

 nished, either separately or conjointly, by air, soil, and water. Plants, with very 

 few exceptions, require soil for the reception of their roots, and as the medium 

 through which they derive the greater part of their nourishment. It should be 

 borne in mind, however, that they are living beings, endowed with certain powers 

 by which they are enabled to take up as food such matters as are best adapted 

 to the particular purposes of their economy ; and that they flourish in propor- 

 tion to the means they enjoy of satisfying their respective wants. It is neces- 

 sary, therefore, to have correct ideas of the nature of soils, and of the circum- 

 stances upon which their difference depends. It has been ascertained long ago 

 that silica, with alumina, lime, and magnesia, form the basis of all soils ; and that 

 of these four elements, in different proportions and in different combinations, 

 all the numerous varieties of soil are composed. The quality of soil is, however, 

 still further diversified by the admixture of animal and vegetable matters, a few 

 salts, alkalies, and metallic oxides. The soils of this country may be very con- 

 veniently divided into three principal classes, viz. the siliceous, or sandy ; the 

 aluminous, or clayey ; and the calcareous, or chalky ; each being named after its 

 predominant component, and each, of course, presenting numerous varieties. 



. SILICEOUS SOIL. 



Of the primary earths above-named, silica is the one that enters most abun- 

 dantly into the composition of the greater number of soils : it occurs in the 

 shape of pebbles, gravel, and sand, of various degrees of fineness ; and of such 

 importance is its presence, that it may be admitted as a general rule, that no 

 soil can be expected to be fertile, which does not contain at least one half of this 

 earth as its basis. A fertile soil near Bristol was found to contain sixty parts 

 in the hundred of silica. A good siliceous sandy soil from a hop-garden in 

 Kent, contained upwards of fourteen parts in twenty of silica. A good turnip- 

 soil from Holkham in Norfolk, afforded eight parts in nine of siliceous sand : 

 and Sir Humphry Davy states, that he has seen a tolerable crop of turnips on 

 a soil of which eleven parts out of twelve consisted of sand. Soils, however, 

 which contain a still larger proportion of siliceous sand, are invariably charac- 

 terised, more or less, by sterility. Such is the soil of Bagshot Heath, which is 



VOL. II. NO. XIX. — SEPTEMBER. F 



