7 *
land, and used as manure ; viz. shell marl, stone or rock marl,and clay marl.
Shell marl has been found and used as manure to the soil indifferent districts. It was at first profusely applied, and crops oftoo great luxuriance were raised. At present from 30 to 40 cartloads are laid on an acre, about 16 cubic feet each load; anddouble that quantity is laid on strong cohesive soils. It is some-times laid on fallow or stubble : but to spread it on grass, in sum-mer, and allow it to lie on the surface for one or more years, isdeemed preferable.
Stone marl lias been found, in some instances, not to contaiamore than IS per cent, of calcareous matter; in others it is richer.It has been laid on land at the rate of from 400 to 600 cart loadsper acre. This heavy labour has made many farmers prefer lime,even when carried from a considerable distance.
Clay marl differs nothing from the last, except that, being soft,its parts separate with more facility, and, being sooner blendedwith the soil, takes quicker effect. Both these are allowed to liesome time spread on the surface.
Marble earth, found in the Isle of Skye , being a pure carbon-ate of lime, need not be farther noticed.
Sea-shells, beds of which have been found in many places a-Jong the shores of Scotland , are applied with success on theneighbouring grounds. They have been sometimes carried coast-wise to distant places. As they are nearly pure carbonate oflime, their effect is admitted to be similar. Corals and corallines,which are also found on the coast, are considered as the same.Nor is the shelly sand, or sea sand, which has been successfullyapplied to ground on the coast, any thing different, except in themixture of silicious earth, which makes it fittest for cohesivesoils.
The last enumerated substances, as calcareous, must operateas lime does. Shell marl contains a large proportion of calcare-ous earth with some dissolved animal matter. When spread onthe surface, it promotes the growth of esculent herbage—it oc-casions large tillage crops; and when the land is gently cropped,and returned to grass, the turf is closer, the grass more plenti-ful and sweeter than before. Its operation is not so quick, butmore durable than that of lime. In some instances, however, ithas been found immediate. It greatly promotes the growth ofclover. But on cold damp soils which have been strongly marl-ed, the crop has been found later, and the grain lighter thanon limed land. * By severe cropping, marled land has beenmuch exhausted. In Stormont and Strathmore , in Perthshire,some fields have been almost laid waste by repeated marling and®ver-cropping : the surface, having been rendered too loose to
* Roxburghshire Report