OBSERVATIONS ON THE NATURE OF SOILS. 



107 



other formations, are moderately fertile : their prevailing character, however, is 

 sterility, more especially when combined with any considerable proportion of 

 magnesia, as in the province of Champagne in France. The same remarks are 

 equally applicable to the limestone districts ; they vary in fertility according to 

 the nature of the subsoil and other circumstances ; many of the valleys being 

 noted for their productiveness ; while the more elevated parts (as well as in the 

 chalk districts) are for the most part remarkable for their sterility. A chalky 

 soil, however, appears to be particularly favourable to the growth of the beech ; 

 the Chiltern Hills are said to have been formerly covered with it, and thus 

 affording shelter to banditti ; " whence the office of Steward of the Chiltern 

 Hundreds, the acceptance of which, though now only nominal, enables a member 

 to vacate his seat in parliament." 



Such are the three principal kinds of soil, and which are named, as already 

 observed, from the primary earth which chiefly abounds in them. It has been 

 remarked by Sir Humphry Davy that the term sandy (siliceous) soil should 

 never be applied to any soil that does not contain, at least, seven eighths of sand ; 

 and that sandy soils which effervesce with acids should be named calcareous sandy 

 soils (as containing chalk or lime), to distinguish them from those that are more 

 decidedly siliceous. So, in like manner, "the term clayey soil should not be 

 applied to any land which contains less than one sixth of impalpable earthy 

 matter, not considerably effervescing with acids." 



The botanist judges of soils from the plants which they spontaneously produce, 

 some plants being found to grow naturally on one soil, but may be sought for in 

 vain on another; thus the common Foxglove (Digitalis purpurea), which delights 

 in a sandy or gravelly soil, is never seen in those parts of Gloucestershire which 

 are situated upon the Cotswold Hills, a most extensive range, and chiefly com- 

 posed of a sandy limestone. On the other hand, the wild parsnep (Pastinaca 

 saliva) may generally be observed by road-sides in a chalky or limestone district, 

 but soon disappears as we enter upon a soil with a sandy or gravelly bottom. 

 From such facts, an attentive observer is enabled to form a tolerably correct 

 opinion of the general character of soils ; but this is by no means sufficient as a 

 guide in cultivation. In order to become acquainted with the real nature of soils, 

 we must have recourse to chemistry, without which it is scarcely possible to 

 arrive at any degree of accuracy. The late Sir Humphry Davy threw great light 

 upon this subject by the publication of his admirable lectures on Agricultural 

 Chemistry; at the same time he very justly observes, "that the results of 

 analyses considered as affording indications of fertility, must necessarily differ 

 according to the variations of climate, situation, and other circumstances. Thus, 

 the power of soils to absorb moisture ought to be greater in warm and dry 

 countries than in cold and moist ones, and when the quantity of fine argillaceous 

 (clayey) earth they contain is larger. Soils likewise which are situated on 

 declivities, ought to be more absorbent than those in the same climate situated 



p 2 



