4 EUROPEAN AGRICULTURE. 



is of a different description, and would 3 by being covered over, 

 be speedily brought into a state of decomposition. Here the 

 expediency of paring and burning is more questionable. 



In the process of burning, it is evident that none of the earthy 

 or mineral constituents, or what are called the inorganic portions 

 of the soil, are consumed. But all the vegetable matter, with 

 the exception of that portion which has become charred in the 

 process, is destroyed. The extreme doctrine of some eminent 

 chemists is, that the hurnus, or vegetable portion of the soil, is 

 of no importance to vegetation ; but universal experience and 

 observation seem to attest that the fertility of soils, with some 

 exceptions, may be ordinarily determined by the quantity of 

 decayed vegetable matter or mould in which they abound. If 

 plants, in fact, derive nothing from the soil but the mineral in 

 gredients which are found in them, yet the humus of the soil 

 may itself be the means of abstracting from the air, and conduct 

 ing to the plants, the nourishment, the carbonic acid, and the 

 ammonia, which they are to obtain from thence.* The humus 

 of the soil serves to render it more friable ; it absorbs moisture 

 from the atmosphere, and it retains heat, and, in these respects, 

 if in no other, contributes to vegetation.! In dissipating this 



* &quot;Humus, in contact with air, gives off carbonic acid.&quot; &quot;The capital 



fact which results from these experiments of Saussure, the deduction directly ap 

 plicable to the theory of manures, is this that humus is dissipated when it is ex 

 posed to the air ; and that, during the slow combustion which it undergoes, it is 

 a constant source of carbonic acid gas.&quot; Boussingault, p. 323. 



&quot; Potash and soda dissolve humus almost completely, causing an evolution of 

 ammonia.&quot; Ibid. p. 321. 



f &quot; There is an important element, which must always be taken into the ac 

 count in estimating the value of soils, no matter what their special composition ; 

 this element is their depth, or thickness. In running a deepish furrow in a cultivated 

 field, we generally distinguish at a glance the depth of the superficial layer, which 

 is commonly designated as the mould, or vegetable earth ; this is a layer gener 

 ally impregnated with humus, and looser and more friable than the subsoil upon 

 which it rests. The thickness of this superficial layer is extremely variable. It 

 is frequently no more than about three inches ; but it is also encountered of every 

 depth, from three or four to twelve or thirteen inches. It must be held an ex 

 ceptional and unusual case, when it has a depth of three feet, or more. Never 

 theless, we do meet with collections of vegetable soil of great depth, deposited 

 by rivers, washed down into the bottoms of valleys, or accumulated on the surface, 

 as in the virgin forests or vast prairies of America. Depth of mould or vegetable 

 soil is always advantageous; it is one of the best conditions to successful agri- 

 cult.mv. Tf wo have depth of soil, and the roots of our plants do not penetrate 



