CALCAREOUS MANURES-APPENDIX. 187 



convertible into hydrogen gas. If the farmer finds, by experiment, that his soil has but a 

 small quantity of oroanic matter, or knows by his practice that it is poor, and not worth 

 more tliau 10s., 15s. or 20s. an acre, he may then conclude that there ought to be 20 per 

 cent, of calcareous earth in it ; but if, on the contrary, it abound with organic matter, and 

 be worth in practice a much larger rent, in that case his marl cart will not be called for, 

 though there be but five per cent, or even less, of calcareous matter."— Young's Essay on 

 Manures— Sect. 2. 



It is scarcely necessary to show, that the opinion of calcareous matter 

 being needed in larger quantities in proportion to the deficiency of pu- 

 trescent matter, is directly opposed to the reasoning of this essay. If a 

 poor soil were made to contain twenty per cent, of calcareous matter, by 

 applying lime, chalk, or marl, the quantity and the expense would be so 

 enormous as not to be justified by any possible return, and in truth, would 

 lessen rather than increase the product of a poor soil. The fact named 

 as strange by Young, that some rich soils contain very small, and others 

 very large proportions of calcareous earth, is easily explained. If a natu- 

 ral soil contains any excess of calcareous earth, even though but one per 

 cent., it shows that there is that much to spare after having served every pur- 

 pose of neutralizing acids and combining with putrescent matter. If there 

 were twenty per cent, more of calcareous matter, it would be useless, 

 until met by an additional supply of putrescent matter. Young's state- 

 ment that some poor soils agree precisely with other rich soils, in their 

 contents of calcareous earth, does not necessarily contradict my doctrine 

 that a proper proportion of calcareous earth will enable any soil to become 

 rich, either in a state of nature, or under mild cultivation, and for the fol- 

 lowing reasons: 



16. 1st. The correctness of Young's analyses may be well doubted; 

 and if he used the then usual process for separating calcareous earth, he 

 was obliged to be incorrect on account of its unavoidable imperfection, as 

 has been already explained at page 36. 2d. It cannot be known positively 

 what was the original state of fertility of most cultivated soils in England, 

 nor whether they were subjected to exhausting or improving cultivation, 

 for centuries before our information from history begins, od. Lime has 

 been there used for a long time, and to great extent ; and chalk and marl 

 were applied as manures during the time of the Roman conquest, as stated 

 by Pliny, (say 1700 years ago) so that it cannot be always known whether 

 a soil has received its calcareous ingredient from nature, or the industry 

 of man. 4th. It is known that severe cropping after liming, and also ex- 

 cessive doses of calcareous earth, have rendered land almost barren; of 

 which the following extracts offer sufficient proof: — 



" Before 1778, [in East Lothian,] the out-field did not receive any dung except what was 

 left by the animals grazed upon it. In many cases, out-field land was limed ; and often 

 with singular advantage. The after management was uniformly bad ; it being customary 

 to crop the limed out-field with barley and oats successively, so long as the crop was 

 worth cutting. In this way numerous fields suffered so severely as to be rendered almost 

 sterile for half a century afterwards." Fai-mer's Magazine, p. 53, vol. xii. 



" An overdose of shell marl, laid perhaps an inch thick, produces for a time large 

 crops. But at last it renders the soil a caput mortuum, capable of neither corn nor 

 grass ; of which, there are too many examples in Scotland, &c. Gentleman Far- 

 mer, p. 378. 



1 7. Yet the last writer (Lord Kames) elsewhere states, (at page 379,) 

 that as much clay marl as contains 1500 bolls, (or 9000 bushels,) of pure 

 calcareous earth to the acre, is not an overdose in Scotland. 



18. " Marl. Of this substance, there are four sorts, rock — slate — clay — and shell 

 marl. The three former are of so heavy a nature that they are seldom conveyed to any 

 distance ; though useful when found below a lighter soil. But shell marl is specifically 



