MARL, an earthy substance found at various depths under the soil, and extensively used for the improvement of land. It consists of cal careous and argillacemea earth, in various proportions, and as the former or the latter prevails, so it is beneficially employed on clays or sands. There are several distinct sorts of marl--clay marl, shell marl, elate mirl, and stone marL The clay marl has probably been formed by the slow deposition of clay suspended In water, and mixed with the particles of decomposed shells. When these shells have retained their form, or appear in fragments in the marl, it is called Aril marl. A considerable compression and a complete decomposition of the shells form slate marl and stone marl. The effect of marl is the same as that of clay and chalk upon sandy soils; on heavy soils its effect is propor tioned to the quantity of calcareous earth which it contains. The peculiar advantage of marl is its readily crumbling to powder by the effect of sir and moisture. l f it Is too oompact to dissolve under these influences, it can only be made useful by burning, and in this case It is only a substitute for limo, its value depending on the proportion of eileareous earth in the marL Marl is often found very near the surface, so as to mix with the soil in ploughing; but unless there be a muilloient depth of soil above, its presence does not Indicate great fertility. It is generally best when tone' at a moderate depth, so Hi to be readily dug out and carted on the adjacent lands. In Norfolk, where a marl containing a largo pro pinion of clay is found in many places under alight soil, it. in frequently spread over the surface at the rate of two or three hundred cart-loads per acre. This dressing, joined to underdraining, makes a wonderful improvement on soils which before were scarcely worth cultivating, owing to their being loose and wet In winter. The clay marl makes them retain sufficient moisture, while the superfluous water is carried off by the drains.
Marl when put fresh upon the land requires some time in order to become effective. It should therefore be Inld on time surface and spread
before winter, leaving it there for a considerable time before it is ploughed in. It is moat advantageous to put it on the land when it is , in grass, and to roll and harrow it repeatedly, in order to expose it to the effect of the air and rains. Alternate frost and thaws greatly assist its pulverisation.
An excellent use of marl is in forming compost with dung awl peat earth. It is laid in layers with the dung and peat, and if the heap is well soaked with urine or the washings of stable-yards, it will In a short time become a most valuable manure for all kinds of soils, Many peat bogs are formed on a marly bottom ; where this is the case, and it can be drained, or the water got rid of in any way, the marl, when laid on the surface, consolidates the peat by its pressure, and soon makes it capable of producing good herbage by converting it into a rich vegetable mould.
The expense of marling land can only be calculated when the distance of the marl and the depth from which it is raised are known ; when it lies in a stratum under the land, it is generally the cheapest plan to open a pit in each field ; for the carriage of the marl is the chief expense. 1Vithiu a distance of two hundred yards from the pit, it is found by experience that the cheapest way of putting it on the laud is by means of men wheeling it in barrows with the help of planks, as is done in digging canals and other similar public works.
It is iu the compound character of certain limes that the subject of marling becomes connected with that of liming. As extraneous matters increase in quantity, and the limo diminishes, the effect of the application of course depends less and less on those considerations which explain the effect of liming, and the influence of the application of marl depends more end more upon the clay or sand, or it may be other things in smaller quantity which are thus conveyed to the Land.