50 CALCAREOUS MANURES— THEORY. 



tion or disintegration of rocks, is received as true by scientific agricul- 

 turists. The soils thus supposed to be formed, receive admixtures from 

 each other, by means of different operations of nature, and after being 

 more or less enriched by the decay of their own vegetable products, make 

 the endless variety of existing soils.* But where a soil, lying on and thus 

 supposed to have been formed from any particular kind of rock, is so situ- 

 ated that it could not have been moved, or received considerable accessions 

 from torrents or other agents, then, according to this theory, the rock and 

 the soil should be composed of the same materials ; and such soils as the 

 specimens, marked 1 1 and 16, (page 41,) would be, Iii<e the rock they touch- 

 ed, nearly pure calcareous earth, instead of being (as they were in truth) 

 destitute, or nearly so, of that ingredient. Such are the doctrines received 

 and taught by Davy, or the unavoidable deductions from them. But, with- 

 out contending for the full extent of this theory of the formation of soils, 

 (because I consider it almost entirely false,) every one must admit that soils 

 thus situated must have received, in the lapse of ages, some accessions to 

 their bulk, from the effects of frost, rain, sun, and air, on the lime-stone in 

 contact with them. All lime-stone soils, properly so called, exhibit certain 

 marked and peculiar characters of color, texture, and products, which can 

 only be derived fi'om receiving into their composition more or less of the 

 rock which lies beneath, or rises above their surface. This mixture will 

 not be denied by any one who has observed lime-stone soils, and reasons 

 fairly, whether his investigation begins with the causes, or their effects. If 

 then all this accession of calcareous earth remains in the soil, why is it that 

 none, or almost none, is discovered by accurate chemical analysis ? Or, if 

 it be supposed not present, nor yet changed in its chemical character, in 

 what possible manner could a ponderous and insoluble earth have made its 

 escape from the soil ! To remove this obstacle, without admitting the ope- 

 ration of acid in making such soils neutral, will be attended with at least 

 as much difficulty, as any arising from that admission being made. 



7th. But we are not left entirely to conjecture that soils were once more 

 calcareous than they now are, if chemical tests can be relied on to furnish 

 proof Acid soils that have received large quantities of calcareous earth 

 as manure, after some time, will yield very little when analyzed. To a 

 soil of this kind, full of vegetable matter, 1 applied, in 1818 and 1821, 

 fossil shells at such a known and heavy rate as would have given to the 

 soil (by calculation) at least three per cent, of calcareous earth, for the 

 depth of five inches. Only a small portion of the shelly matter was very 

 finely divided when applied. Since the application of the greater part of 

 this dressing, (only one-fourth having been laid on in 1818,) no more than 

 six years had passed before the following examinations were made (at end 

 of 1826); and the cultivation of five crops in that time, three of which 

 were horse-hoed, must have well mixed the calcareous earth with the soil. 

 Three careful examinations gave the following results: 



No. 1. — 1000 grains yielded 7^ of coarse calcareous earth, (fragments of 

 shells,) 



And less than \ of finely divided. 



* Agr. Chem. p. 131. Also Treatise on Agriculture, (by General Armstrong,) quoted 

 in a preceding page (3;{) of this essay. 



