in natural history, a genus of fossils; being bright and beautiful stones composed of small separate concretions, moderately hard, not giving fire with steel, fermenting with and soluble in acid menstrua, and calcining in a slight fire.—The word comes from the French marbre, and that from the Latin marmor, of the Greek μάρμαρον, to "shine or glitter."

The colours of marbles being a very obvious and striking character, they are arranged according to them in the following divisions. 1. Of the white plain marbles there are two sorts; the Parian marble of the ancients, and statuary marble of the moderns, an extremely bright and elegant marble; and the Carrara marble, a very fine marble, more compact and close than the former, but less bright. 2. Of the plain yellowish marbles there is only one sort, which is a hard, pale yellow, and glossy marble, found in many parts of Italy. 3. Of the bluish and black marbles there are a great many species, as the China marble, basaltes, &c. 4. Of the plain green marbles there is only one kind, the Laconian marble of the ancients. 5. The pale coloured or whitish brown, commonly called Derby marble. 6. The green marbles with shells. 7. The black carolloide marble, with and without shells. 8. Of the white variegated marbles there are a great many species, variegated with purple, brown, red, blue, &c. 9. Of the brown variegated marbles there are likewise several sorts, some with red veins, others with white, black, or brown veins. 10. Of the yellow-veined and variegated marbles, some are veined with purple, and others with blue. 11. Of the black variegated marbles, some are veined with white, and others with blue, yellow, red, &c. 12. The green variegated marbles are likewise distinguished by the colour of their veins. 13. The gray spotted marbles are variegated, some with black, and others with green spots. 14. The red variegated marble is the brocatello of the Italians, with white and gold veins.

Marble, when chemically examined, appears to consist of calcareous earth united with much fixed air; and is, like limestone or chalk, capable of being converted into a strong quicklime.—Dr Black derives the origin of marbles, as well as limestone and marle, from the same source, viz. from the calcareous matter of shells and lithophyta. In one kind of limestone known by the name of Portland stone, and consisting of round grains united together, it was supposed to be composed of the spawn of fish; but comparisons of other phenomena have explained it. It is plain that it has been produced from a calcareous sand, which is found on the shore of some of the islands in the southern climates. By the constant agitation the softer parts are wore off, and the harder parts remain in the form of particles that are highly polished, and which are afterwards gradually made to concrete together by causes of which we have yet no knowledge.—There are indeed some few of the limestones and marbles in which we cannot discover any of the relics of the shells; but there are many signs of their having been in a dissolved or liquefied state; so we cannot expect to see the remains of the form of the shells: but even in many of the marbles that have the greatest appearance of a complete mixture, we still find often the confused remains of the shells of which they have been originally composed.

We should still find it difficult to conceive how such masses should have derived their origin from shells; but, considering the many collections that we have an opportunity of seeing in their steps towards this process, and a little concreted together, so that by their going a step further they might form limestone and marbles, we shall soon see the possibility of their being all produced in the same manner. Thus vast quantities of shells have been found in the province of Turin in France; and indeed there is no place where they have not been found. The lithophyta likewise seem to be a very fruitful source of this kind of earth. In the cold climates, where the moderate degree of heat is not so productive of animal-life, we have not so much opportunity of observing this; but in the hot climates, the sea, as well as the land, swarms with innumerable animals; and, at the bottom, with those that produce the corals and madreporites. We learn from the history of a ship that was sunk in a storm in the Gulf of Mexico, the vast growth there is of these bodies. About 30 years after, they attempted to dive into it to get out a quantity of silver; but they found great difficulty in getting it, from the ship being overgrown with coral. Sir Hans Sloan, in the Philosophical Transactions, and in his history of Jamaica, observes, that the ship's timber, the iron, and money, were all concreted by the growth of the calcareous matter. So in a tract of many thousands of years the quantity of it should be very great; and as this is going on through a very great extent of the bottom of the sea, it will produce very extensive as well as maffy collections of calcareous matter.

Colouring Marble. This is a nice art; and, in order to succeed in it, the pieces of marble on which the experiments are tried, must be well polished, and free from the least spot or vein. The harder the marble is, the better will it bear the heat necessary in the operation; therefore alabaster and the common soft white marble are very improper for performing these operations upon.

Heat is always necessary for opening the pores of marble, so as to render it fit to receive the colours; but the marble must never be made red-hot; for then the texture of it is injured, and the colours are burnt, and lose their beauty. Too small a degree of heat is as bad as one too great; for, in this case, though the marble receives the colour, it will not be fixed in it, nor strike deep enough. Some colours will strike even cold; but they are never so well sunk in as when a just degree of heat is used. The proper degree is that which, without making the marble red, will make the liquor boil upon its surface. The menstruums used to strike in the colours must be varied according to the nature of the colour to be used. A lixivium made with horse's or dog's urine, with four parts of quicklime, and one of pot-ashes, is excellent for some colours; common ley of wood-ashes is very good for others; for some, spirit of wine is best; and lastly, for others, oily liquors, or common white-wine.

The colours which have been found to succeed best with the peculiar menstruums, are these. Stone-blue dissolved in six times the quantity of spirit of wine, or of the urinous lixivium, and that colour which the painters call Sanguis, dissolved in common ley of wood-ashes. An extract of saffron, and that colour made of backthorn berries, and called by painters sap green, both succeed well when dissolved in urine and quicklime; and tolerably well when dissolved in spirit of wine. Vermilion, and a very fine powder of cochineal, also succeed very well in the same liquors. Dragon's-blood succeeds in spirit of wine, as does also a tincture of logwood in the same spirit. Alkanet-root gives a fine colour: but the only menstruum to be used for it is oil of turpentine; for neither spirit of wine, nor any lixivium, will do with it. There is another kind of sanguis draconis, commonly called dragon's blood in tears, which, mixed with urine, gives a very elegant colour.

Besides these mixtures of colours and menstruums, there are other colours which must be laid on dry and unmixed. These are, Dragons-blood of the purest kind, for a red; gamboge, for a yellow; green wax, for a green; common brimstone, pitch, and turpentine, for a brown colour. The marble for these experiments must be made considerably hot, and then the colours are to be rubbed on dry in the lump. Some of these colours, when once given, remain immutable; others are easily changed or destroyed. Thus, the red colour given by dragon's-blood, or by a decoction of logwood, will be wholly taken away by oil of tartar, and the polish of the marble not hurt by it.

A fine gold colour is given in the following manner: Take crude sal ammoniac, vitriol, and verdigris, of each equal quantities. White vitriol succeeds best; and all must be thoroughly mixed in fine powder.

The staining of marble to all the degrees of red or yellow, by solutions of dragon's-blood or gamboge, may be done by reducing these gums to powder, and grinding them with the spirit of wine in a glass mortar. But, for smaller attempts, no method is so good as the mixing a little of either of those powders with spirit of wine in a silver spoon, and holding it over burning charcoal. By this means a fine tincture will be extracted; and, with a pencil dipt in this, the finest traces may be made on the marble while cold; which, on the heating of it afterwards, either on sand, or in a baker's oven, will all sink very deep, and remain perfectly distinct on the stone. It is very easy to make the ground-colour of the marble red or yellow by this means, and leave white veins in it. This is to be done by covering the places where the whites are to remain with some white paint, or even with two or three doubles only of paper; either of which will prevent the colour from penetrating. All the degrees of red are to be given to marble by this gum alone; a slight tincture of it, without the assistance of heat to the marble, gives only a pale flesh-colour; but the stronger tinctures give it yet deeper; to this the assistance of heat adds greatly; and finally, the addition of a little pitch to the tincture, gives it a tendency to blackness, or any degree of deep red that may be desired.

A blue colour may be given also to marble by dissolving turpentine in lixivium, in lime and urine, or in the volatile spirit of urine; but this has always a tendency to purple, whether made by the one or the other of these ways. A better blue, and used in an easier manner, is furnished by the Canary turpentine, a substance well known among the dyers. This needs only to be dissolved in water, and drawn on the place with a pencil: it penetrates very deeply into the marble; and the colour may be increased, by drawing the pencil wetted afresh several times over the same lines. This colour is subject to spread and diffuse itself irregularly: but it may be kept in regular bounds, by circumferring its lines with beds of wax, or any such substance. It is also to be observed, that this colour should always be laid on cold, and no heat given even afterwards to the marble: and one great advantage of this colour is, that it is therefore easily added to marbles already stained with other colours, is a very beautiful tinge, and lasts a long time.

For other methods of staining marble, see Chemistry, p. 197.

Arundel Marbles, ancient marbles with a chronicle of the city of Athens inscribed on them many years before our Saviour's birth; presented to the university of Oxford by Thomas earl of Arundel, whence the name.