MARLING
(Ibid., Letter XVIII, p. 198)
As to manures, marle is the grand one, which is found under all this country (Lancashire) and generally within sixteen or twenty inches of the surface ... it lies in beds, many of them of a vast depth, the bottoms of some pits not being found. It is white, and as soft and soapy as butter. They lay about a hundred two-horse cartloads to an acre, but some farmers less, on to lays[31] and stubble. It lasts a good improvement for twenty years: costs about £4 10s. 0d. an acre. Marle is their principal manure, both white, black, blue, sandy and some small marle. They sometimes find perfect cockle and periwinkle shells nine yards deep in beds of marle. It does best on light soil.