386 LORD KAMES AND SIR JOHN SINCLAIR. 



"An overdose of shell marl [that from under peat y above described], 

 laid perhaps an inch thick, produces for a time large crops. But at last it 

 renders the soil a caput mortuum, capable of bearing neither corn nor 

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

 man Farmer, p. 378. 



23. Yet the last-quoted 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 over- 

 dose in Scotland. 



The next following evidences have been referred to, and some 

 of them at greater length, in previous parts of this essay. They 

 will be again adduced here, because of their peculiar importance in 

 sustaining my positions. The particular opinions here to be quoted 

 are from writers of high character and authority, as scientific agri- 

 culturists, or chemists. The names of Sinclair, Davy, and Morton 

 (and also Young, before quoted), deservedly stand among the 

 highest. Moreover, they are all niode-rn authorities. They seve- 

 rally had all the lights on calcareous manures which existed before 

 the last thirty years (or later) ; and certainly each of them, well knew 

 what was true marl, its mineralogical and chemical character, and 

 also what was calcareous soiL Sir John Sinclair will be the first 

 of these quoted, 



24. " 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 

 seldorf conveyed to any distance ; though useful when found below a lighter 

 soil, to which they can be applied without incurring much expense. But 

 shell marl is specifically lighter, and- consists entirely o-f calcareous matter 

 (the broken and partially decayed shells of fish), which may be applied as- 

 a top-dressing to wheat and grass, when it would be less advantageous to 

 use quick-lime." [This is the kind of manure referred to in extract 12, and 

 there more particularly described.] "In Lancashire and Cheshire, clay, 

 or red marl, is the great source of fertilization, &c." "The quantity 

 used is enormous ; in many cases about three hundred middling cart loads 

 per acre, and the fields are sometimes so thickly covered as to have the 

 appearance of a red soiled fallow, fresh ploughed". Sinclair's Code of Ag- 

 riculture, Amer. ed. (Hartford) p. 138, and 5th London ed. 



This account of the Lancashire improvements made by red clay 

 marl closes with the statement that " the effects are represented to 

 be beneficial in the highest degree," which is fully as exact an ac- 

 count of profit, or increased production, as we can obtain of any 

 other marling. Throughout, there is no hint as to the calcareous 

 constituents of the soil or the manure, or whether either rock, clay, 

 or slate marls, generally, are valuable for that or for other reasons; 

 nor indeed could we guess that they contained any calcareous earth, 

 but for their being classed with many other substances, under the 

 general head of calcareous manures. 



But we may learn from other sources that the " red marl" of 

 Lancashire is calcareous, and that the soil to which it was applied 

 is also calcareous. This character of the marl is distinctly stated 



