MARBLE, in its strict and proper sense, is a rock crystallized in a saccharoidal manner, having the fracture of loaf-sugar, and composed of carbonate of lime, either almost pure when the color is white or combined with oxide of iron. or other impurities which give various colors to it. But many other kinds of stone are popularly included under this ' title. Indeed, any limestone rock sufficiently compact to admit of a polish is called marble. It is only in this vague sense that the indurated amorphous rocks used in'this country can receive this name. Such are the black, red, gray, and variegated limestones of the old red sandstone period, found in Devonshire, which are very beautiful from the numbers of exquisitely preserved corals Which abound in them; the marbles of the car boniferous series from Flintshire, Derbyshire, and Yorkshire, so full of encrinites; the shell marbles from the oolite rock.s at Rance, Stamford, and Yovil; and the dark Purbeck and Petworth marbles, beautifully " figured" with shells, from the wealden strata, which were so much u,sed by the architects of the middle ages.
Saccharine or statuary marble is a white, fine-g,rained rock, resembling loaf-sugar in .color and texture, working freely in every direction, not liable to splinter, and taking a fine polish. Of the marbles used by the ancients the most famous are: ParIan marble, a finely granular and very durable stone, With a waxy appearance when polished. Some of the finest Grecian sculptures were formed of this marble, among others the famous Venus de Medici. The marble of Pentelicus was at one time preferred by the Greeks to Parlay, because it was whiter and finer grained. The Parthenon was entirely built of
it, and many famous statues still remain which were executed in this marble, but they are always more or less weathered, never retaining the beautiful finish of the Parian statues. The quarries at Carrara were known to the ancients, but they have been more extensively wrought for modern sculptors, who use this marble chiefly. It is a fine grained, pure white marble, but is so often traversed by gray veins that it is difficult to get large blocks free from them. Of colored marbles, the best known are the rosso antico, a deep blood-red, sprinkled with minute white dots; verde antico, a clouded green producea by a mixture of white marble and green serpentine; giallo antic°, a deep yellow, with black or yellow rings; and nero antico, a deep black marble.
The crystalline structure of marbles may be the original condition in which the rock was formed as a chemical deposition, in the same manner as some stalactites are crystal line, but there can be no doubt that they principally owe their structure to metamorphic .action which has taken place subsequent to their deposition. This action having, at the ' same time, destroyed all trace of fossils, marbles were considered formerly as belonging to the primitive or metamorphic series of rocks; but, while they generally are members •of one of the paleozoic formations, it is now known that some of the statuary marbles of Greece and Italy are secondary, and others even tertiary limestones.