80

mous *; and of the different sorts of marl, thatwhich is most calcareous is best; the siliciousnext best; limestone-gravel best of all; andargillaceous marl least advantageous f.

Clayey soils are defective both in constitu-tion and in texture; they want the calcareousingredient and coarse sand. Calcareous marlsupplies the calcareous ingredient chiefly: lime-stone-gravel both. The other marls supplythem in a lesser degree. If the clay be ana-lysed, and its proportion of sand and argillknown, the species of marl most advantageouslyapplicable may be determined still better. Forinstance, if the argill notably exceeds or evenamounts to the proportion of 40 or 50 percwt. calcareous marl or limestone-gravel arethe best improving manures, as they containmost of the calcareous ingredient; but if thesilicious ingredient amounts to 75 or 80 percwt. as it sometimes does, argillaceous marl ismost suitable.

* 4th Young’s Eastern Tour, 404. 1st Body of Agri-culture, 104, 108.t Ibid, 108.