56 CALCAREOUS MANURES-THEORY. 



as fast as formed, united with the lime in the soil. At last these two 

 principles balanced each other, and the soil was no longer calcareous, but 

 neutral. Instead of its former ingredient, carbonate of lime, it was 

 now supplied with a vegetable salt of lime. This change of soil does 

 not affect the natural growth, which remains the same, and thrives as well 

 as when the soil was calcareous ; and when brought into cultivation, the 

 soil is equally productive under all crops suited to calcareous soils. If the 

 supplies of vegetable matter continue, the soil may even become acid in 

 some measure, as may be evidenced by the growth of sorrel — but without 

 losing any of its fertility before acquired. The degree of acidity in any 

 one soil frequently varies ; it is increased by the growth of such plants as 

 delight to feed on it, and by the decomposition of all vegetable matters. 

 Hence the longer a poor field remains at rest, and not grazed, the more 

 acid it becomes ; and this evil keeping pace with the benefits derived, is the 

 cause why so little improvement, or increased product, is obtained from 

 putting acid soils under that mild treatment. Cultivation not only prevents 

 new supplies, but also diminishes the acidity already present in excess, by 

 exposing it to the atmosphere ; and therefore the more a soil is exhausted, 

 the more will its acidity be lessened. 



We have seen from the proof furnished by the analysis of wood ashes, 

 that even poor acid soils contain a little salt of lime, and therefore must 

 have been slightly calcareous at some former time. But such small pro- 

 portions of calcareous earth were soon equalled, and then exceeded, by the 

 formation of vegetable acid, before much productiveness was caused. The 

 soil being thus changed, the plants suitable to calcareous soils died off", and 

 gave place to others which produce, as well as feed and thrive on, acidity. 

 Still, however, even these plants furnish abundant supplies of vegetable 

 matter, sufficient to enrich the land in the highest degree ; but the antiseptic 

 power of the acid prevents the leaves from rotting for years, and even then 

 the soil has no power to profit by their products. Though continually 

 wasted, the vegetable matter is continually again forming, and always pre- 

 sent in abundance ; but must remain almost useless to the soil, until the 

 accompanying acidity shall be destroyed. 



It may well be doubted whether any soil destitute of lime in every form 

 would not necessarily be a perfect barren, incapable of producing a spire of 

 grass. No soil thus destitute is known, as the plants of all soils show in 

 their ashes the presence of some lime. But it is probable that our sub-soils, 

 which, when left naked by the washing away of the soil, are so generally 

 and totally barren, are made so by their being entirely destitute of lime in 

 any form. There is a natural process regularly and at all times working to 

 deprive the sub-soil of all lime, unless the soil is abundantly supplied. 

 What constitutes soil, and makes the strong and plain mark of separation 

 and distinction between the more or less fertile soil and the absolutely sterile 

 sub-soil beneath 1 The most obvious cause for this difference which might 

 be stated, is the dropping of the dead vegetable matter on the surface ; but 

 this is not sufficient alone to produce the effects, though it may be so when 

 aided by another cause of more power. When the most barren surface earth 

 was formed or deposited by any of the natural agents to which such effects 

 are attributed by geologists, it seems reasonable to suppose that the surface 

 was no richer than any lower part of the whole upper stratum so depo- 

 sited. If, then, a very minute proportion of lime had been equally dis- 

 tributed through the body of poor earth to any depth that the roots of 

 trees could penetrate, it would follow that the roots would, in the course 

 of time, take up all the lime, as all of it would be wanting for the 

 support of the trees ; and their death and decay would afterwards leave 



