1838] 



FARMERS' REG 1ST Jill. 



623 



tens they contain not being attnicied by the earthy 

 constituent parts oC the soil, are more Hahle to be 

 deconiposccl l>y liie action ol' the alinosphere, or 

 carried oti liuin them by water. 



In most of the black ami brown rich vegetalile 

 iDouid?. the earths seem to lie in combinaiiun with 

 a pecuHar extractive matter, afforded during the 

 decomposition ot vegetables : this is slowly ial<en 

 up, or attracted (iom the earths by water, and ap- 

 |)ears fo constitute a jiiime cause of the fertility 

 of the soil. 



The standard of fertility of soils fir different 

 plants must vary with the climate ; and must be 

 particularly influenced by the quantity of rain. 



The power of soils to absorb moisture ought fo 

 be mucli greater in warm or dry countries than in 

 cold and inoist ones ; and the quantity of clay, or 

 vegetable or animal matter they contain, greater. 

 Soils also on declivities ought to be more absor- 

 bent than in plains or in the bottom of valleys. 

 Their productiveness likewise is inl]uenced by tlie 

 nature of the sub-soil, or the stratum on which 

 they rest. 



When soils are immediately situated upon a bed 

 of rock or stone, they are much sooner rendered 

 dry by evaporation, than where the sub-soil is ol' 

 clay or marl : and one cause of the great fertility 

 of some lands in the moist climate of Ireland is 

 the proximity of the rocky strata to the soil. 



A clayey sub-soil will sometimes be of material 

 advantage to a sandy soil ; and in this case it will 

 retain moisture in such a manner as to be capable 

 of supplying that lost by the earth above, in con- 

 sequence of evaporation, or the consumption of it 

 by plants. 



A sandy, or gravelly sub-soil, often corrects the 

 imperfections of too great a degree of absorbent 

 power in the true soil. 



In calcareous countries, where the surface is a 

 species of marl, the soil is often found only a lew 

 inches above the limestone ; and its fertility is 

 not impaired by the proximity of the rock : though 

 in a less absorbent soil, this situation would occa- 

 sion barrenness ; and the sandstone and limestone 

 hills in Derbyshire and North Wales may be 

 easily distinguished at a distance in summer by the 

 differenttintsof the vegetation. The grass on the 

 sandstone hills usually a()pears brown and burnt 

 up ; that on the limestone hills, flourishing and 

 green. 



In devoting the different parts of an estate fo 

 the necessary crops, it is perfectly evident from 

 what has been said, that no ireneral principle can 

 be laid down, except when all the circumstances 

 of the nature, composition, and situation of the 

 soil and sub-soil are knov/n. 



The methods of cultivation, likewise, must be 

 diH'erent for different soils. The same practice, 

 which will be excellent in one case, may be de- 

 structive in another. 



Deep ploughing may be a very profitable prac- 

 tice in a rich thick soil : and in a fertile shallow 

 soil, situated upon cold clay or sandy sub-soil, it 

 may be extremely prejudicial. 



In a moist climate, where the quantity of rain 

 that falls annually, equals fi-om 40 to 60 inches, 

 as in Lancashire, Cornwall, and some parts of 

 Ireland, a siliceous sandy soil is much more pro- 

 ductive than in dr}' districts ; and in such situa- 

 tions, wheat and beans will require a less cohe- 

 rent and absorbent soil than in drier situations ; 



I and plants having bulbous roots will flourish in a^ 

 soil containing as much as 14 parts out of 15 of 

 I sand. 



I Even the exhausting powers of crops will be in- 

 ' fluenced by like circumstances. In cases where 

 i plants cannot absorb sufficient moisture, they 

 I must take up more manure. And in Ireland, 

 i Cornwall, and the Western Highlands of Scot- 

 j land, corn will exhaust less than in dry inland si- 

 tuations. Oats, particularly in dry climates, are 

 impoverishing in a much higher degree than in 

 moist ones. 



Soils appear to have been oriirinally produced in 

 consequence of the decomposition of rocks and 

 strata. It often happens, that soils are found in 

 an unaltered slate upon the rocks from which they 

 were derived. It is easy to form an idea of the 

 manner in which rocks are converted into soils, by 

 referring to the instance of soft grfl>i//e, or porce- 

 lain granite. This substance consists of' three in- 

 gredients, quartz, feldspar, and mica. The quartz 

 is almost pure siliceous earth, in a crystalline 

 form. The feldspar and mica are very compound- 

 ed substances ; both contain silica, alumina, and 

 oxide of iron : in the feldspar there is usually lime 

 and potassa ; in the mica, litne and magnesia. 



When a granitic rock of this kind has been long 

 exposed to the influence of air and water, the lime 

 and the potassa contained in its constituent parts 

 are acted upon by water or carbonic acid ; and the 

 oxide of iron, which is almost always in its least 

 oxided state, tends to combine with more oxygen ; 

 the consequence is, that the felpspar decomposes, 

 and likewise the mica, but the first the most rapidly. 

 The feldspar, v.-hich is as it were the cement of 

 the stone, forms a fine clay : the mica partially de- 

 composed, mixes with it as sand; and the unde-_ 

 composed quartz appears as gravel, or sand of 

 different degrees of fineness. 



As soon as the smallest layer of earth is formed 

 on the surface of a rock, the seeds of lichens, 

 mosses, and other imperfect vecetables which are 

 constantly floating in the atmosphere, and which 

 have made it their resting-place, begin to vege- 

 tate ; their death, decomposition, and decay, af- 

 ford a certain quantity of organizable matter, 

 which mixes with the earthy materials of the 

 rock : in this improved soil more perfect plants are 

 capable of subsisting ; these in their turn, absorb 

 nourishment from water and the atmosphere ; and 

 after perishing, aflbrd new materials to those al- 

 ready provided : the decomposition of the rock 

 still continues ; and at length by such slow and 

 gradual processes, a soil is formed in which even 

 forest trees can fix their roots, and which is fitted 

 to reward the labors of the cultivator. 



In instances Avhere successive generations of 

 vegetables have grown upon a soil, unless part of 

 their produce has been carried off' by man, or con- 

 sumed by animals, the vegetable matter increases 

 in such a proportion that the soil approaches td a 

 peat in its nature ; and if in a situation where it 

 can receive water from a higher district, it becomes 

 spongv, and permeated with that fluid, and is gra- 

 dually rendered incapable of supporting the nobler 

 classes of vegetables. 



Many peat-mosses seem to have been formed 

 by the destruction of forests, in consequence of 

 the imprudent use of the hatchet by the early 

 cultivators of the country in which they exist : 

 when the trees are felled in the outskirts of a wood, 



