a kind of calcareous earth, very much used in agriculture as a manure. See Agriculture, p. 169, 170.

Marle is dug in many places of Great Britain and Ireland. In digging for it in Ireland, they meet with horns and other curious fossils. The marle always lies in the bottoms of low bogs, and is found by boring with augers made for that purpose. It usually lies at five, seven, or nine feet depth. The obtaining it in many places is attended with very considerable expenses in draining off the water. The manner of digging it is this: They employ six able labourers and a supernumerary; and these cut up a hole of 12 feet square, which is supposed a pit that this number of men can manage in one day. Two men dig, two throw it up, and two throw it by, and the supernumerary man supplies defects on all occasions. For the first three feet they dig through a fuzzy earth, fit for making of turf or fuel. Under this lies a stratum of gravel, of about half a foot; under this often, for three feet more, there is a more kindly moss, which would make better fuel. This lower stratum is always full of fossil wood, which is usually so soft, that the spade cuts as easily through it as through the earth it lies in. Under this, for the thickness of about three inches, is found a series of leaves, principally of the oak. These appear very fair to the eye, but fall to pieces on being touched; and this stratum is sometimes interrupted by vast heaps of seed, which seem to be broom or furze seed. In some places there appear berries of different kinds, and in others several species of sea-plants; all lying in the same confused manner as the oak-leaves. Under this vegetable stratum there lies one of blue clay, half a foot thick, and usually full of sea-shells. This blue clay is not so tough as common clay; but is thrown carefully up, and used as marle in some places. Under this always appears the true marle; the stratum of which is usually from two to four feet thick, and sometimes much more.—This marle looks like buried lime, and is full of shells; which are usually of a small size, and of the periwinkle kind; but there are several other sorts at times found among them. Among this marle, and often at the very bottom of it, are found great numbers of very large horns of the deer kind, which are vulgarly called elk's horns. These, where they join to the head, are thick and round; and at that joining there grows out a branch, which is about a foot long, and seems to have hung just over the creature's eyes: it grows still round for about a foot above this; and then spreads out broad, and terminates in branches long and round, terminating with a small bend. The labourers are obliged to work in a hurry in all these pits, so that they seldom bring out the horns whole. There are also, at times, found the leg-bones and other parts of the skeletons of the same beasts; but this more rarely, only a few Dr Black is of opinion, that all kinds of marle derive their origin from the calcareous matter of shells and lithophyta.

Shell-marle, says he, is composed of the shells of aquatic animals, which are sometimes very entire, and often decayed or mixed down with other earthy substances. Examining this matter as occurring in different places, it may be distinguished into fresh-water marle, and the marle of sea-shells. Of the first we have an example in the Meadow at Edinburgh. Wherever the soil is turned up to the depth of six inches, a quantity appears. It is composed of the shells of a small freshwater snail or welk. This animal, when alive, is not easily discernible, the shell being much of the same obscure colour as the stones covered with the water. But we can observe a great number of them in all running brooks and other collections of fresh water; and as the animal dies the shells are deposited where the water stagnates in very great quantity. That composed of sea shells, constitutes greater collections that are found in innumerable places now far removed from the sea. That most particularly described by Reaumur is a collection of this kind in a province of France, and at Turin. That part of the country where it is found is computed to contain 80 square miles of surface; and wherever they dig to a certain depth, they find this collection of shells: the country at present is 108 miles from the sea. They find the marle eight or nine feet below the surface, and they dig it to the depth of 20 feet. It is still deeper, but they find it too expensive to search for it. He supposes it to be only 18 feet deep; and even at this depth the quantity will appear enormous. It will amount to 140 millions of cubic fathoms of shells that are mostly decayed and broken into fragments, and mixed with other marine productions, as millipores, madriposes, and other coralline bodies, which are all productions of the sea.