Marle, a kind of calcareous earth, which is often and advantageously employed as a manure. It is found in various parts of Britain, and generally lies at the bottom of low bogs.
Marie is divided into three species ; calcareous, argillaceous, and siliceous or sandy ; all of which are composed of chalk and clay, so as to crumble with greater or less facility, on being exposed to the atmosphere. They are of a soft, unctuous nature, and dissolve speedily after rain : when dry, they slacken in the same manner as lime, and are at length converted into a very fine powder. Their quality varies according to the soil under which they are deposited : the Norfolk made is held in the greatest esteem; but the most valuable is that found near the sea, or large rivers.
1. Calcareous Marie is, in general, of a yellowish-white or yellowish-grey colour, but in some places of a brown or red cast. It is commonly discovered a few feet be-1 neath the surface of the soil, and on the sides of hills, or on the banks of rivers flowing through calcareous countries. This species of marle is mostly of a loose texture; and, though sometimes moderately coherent, yet it seldom possesses a y hardness, in which state it is called stone-marle. When it is so thin as to be called paper-marle, it is frequently mixed with shells; on which account it is called shell marle, and is reputed to be the best sort. It effervesces with acids ; when pulverized, it feels dry be tween the fingers; and, if immersed in water, it readily crum-bles to pieces, but does not form a viscid mass.
2. A rgillaceous marle is of a grey, brown, or reddish-brown colour ; g harder, and more unctuous, than the former species, and adherin to the tongue. It effervesces with aqua fortis, or spirit of salt, but not with vinegar: in water, it dissolves more slowly; and, if it be exposed either to air or moisture, it does not moulder so quickly as the calcareous kind.
3. Siliceous or sandy Marie, contains a greater proportion of sand, than of chalk or clay. This species is of abrownish-grey or lead colour; it is, in general, friable and flaky, but sometimes forms very hard lumps. It effervesces with acids, but neither dissolves in water, nor moulders so speedily as either of the two former kinds.—Marle affords an excellent manure for sandy, dry, gravelly, or light lands of any kind ; it likewise produces very beneficial effects on mossy and clayey soils; provided a due proportion be applied, and afterwards perfectly dissolved.
The quantity necessary to be used, varies according to the nature of the soil; but the utmost caution is requisite; because, if too large a portion be scattered on the land, it cannot be easily removed ; and, if too little be employed, the deficiency may be readily supplied. On sandy, gravelly, or light soils, it will be advisable to spread as much as will form a thick coat, in order to bind and stiffen the ground. But, of whatever nature the land may be, the most judicious cultivators recommend such a portion to be laid on it, as will form a thin coat over the whole surface.
The proper season for marling, is the summer; as this kind of manure is then perfectly dry, and not only lighter, but also more easily reducible to powder. Marie, however, may be advantageously spread during the winter-frosts ; as, in the latter season, there are few opportunities of performing other labours of the field.
Previously to marling, the land ought to be diligently cleared from all weeds, and rendered level, both with the brake and the common harrow, so that the marle may be equally spread on the surface; where it should be suffered to lie during the winter. In the month of February, and in dry weather, it will be proper to draw a bush-harrow, well weighted, over the land, that the marle may be uniformly distributed; but, as this manure is very ponderous, and sinks to the bottom of the furrow, if injudiciously ploughed in, it has been suggested to turn it into an ebb-furrow for the first crop : during the growth of the latter, the marle will incorporate with, and become a part of the soil, from which it does not readily separate. So permanent, indeed, are its fertilizing properties, that, if land be properly marled, it will continue arable for the space of 12 or 14 years; and, for pasture, during a much longer period.
As marle affords so valuable a manure, it will be useful to point out a few characteristics, by which it may be distinguished from different substances that resemble it. For this purpose, a small mass or lump should be exposed to the air: if genuine, it will, in a short time, by the action of the dews, nitre, etc. crumble into small pieces; and there will likewise appear a hoary or whitish congelation on the side accessible to the rays of the sun.— Another method consists in reducing the marle, when dry, to small particles, which are to be thrown into a coal-fire; -where, if it be native or pure, it will crackle in a manner similar to salt. But the most certain criterion is, to break a small piece of dry marle into a glass of pure water; in which, if bstance be of the genuine d, it will speedily dissolve ; g a soft, almost impalpa-pa>te, and throwing up many bubbles or sparkles to the sur-.:oftbe water. The experiment may be repeated with vinegar, in which fluid the effervescency will be considerably stronger : in both cases, however, it will be necc ry to keep the glass steady; as otherwise, it it be agitated, the intestine motion cannot be distinctly observed.
A good artificial marle may be prepared, by mixing equal quantities of pure clay and lime, in alternate layers, so as to form a heap, which should be exposed to the winter frost : this compound is well calculated for light lands ; but, if the soil be strong and heavy, it will be necessary to substitute loam and sand for the clay.—Such compositions may be usefully employ-re marle is not easily procured ; as they will amply repay the labour bestowed on mixing them, being little inferior to the genuine calcareous earth.