The brown and yellow colours which stalagmitic marbles usually present are due to the presence of oxide of iron. This colouring matter gives special characters to certain stones, such as the giallo antico, or antique yellow marble of the Italian antiquaries. Siena marble is a reddish mottled stone obtained from the neigh bourhood of Siena in Tuscany; and a somewhat similar stone is found in King's county, Ireland. True red marble is by no means common, but it does occur, of bright and uniform colour, though in very small quantity, in the Carboniferous limestone of Derby shire and north-east Staffordshire. The red marble called rosso antico is often confounded with the porfido rosso antico, which is really a mica-hornblende-porphyrite owing its red colour to the mineral withamite.
Fire marble is a brown shelly limestone containing ammonites and other fossil shells, which present a brilliant display of iri descent colours, like those of precious opal. It occurs in rocks of Liassic age at the lead-mines of Bleiberg in Carinthia, and is worked into small ornamental objects.
Although crystalline marbles fit for statuary work are not found to any extent in Great Britain, the limestones of the Palaeozoic formations yield a great variety of marbles well suited for architectural purposes. The Devonian rocks of south Devon are rich in handsome marbles, presenting great diversity of tint and pattern. Plymouth, Torquay, Ipple pen, Babbacombe and Chudleigh may be named as the principal localities. Many of these limestones owe their beauty to the fossil corals which they contain, and are hence known as "madre pore marbles." Of far greater importance, however, are the mar bles from the Carboniferous or Mountain Limestone, whence British marbles are mainly derived. Marbles of this age are worked in Derbyshire and Yorkshire, in the neighbourhood of Bristol, in North Wales, in the Isle of Man, and in various parts of Ireland ; one of the most beautiful is the "encrinital marble," a material which owes its peculiarities to the presence of numerous encrinites, or stone-lilies, fossils which, when cut in various direc tions, give a characteristic pattern to the stone. The joints of the stems and arms are known from their shape as "wheel-stones," and the rock itself has been called "entrochal marble." The most beautiful varieties are those in which the calcareous fossils ap pear as white markings on a ground of grey limestone. In Bel gium a black marble with small sections of crinoid stems is known as petit granit, while in Derbyshire a similar rock, crowded with fragments of minute encrinites, is termed "bird's-eye mar ble."
Perhaps the most generally useful marbles yielded by the Carboniferous system are the black varieties, which are largely employed for chimney-pieces, vases, etc. The colour of most black limestone is due to the presence of bituminous matter. Such limestone commonly emits a fetid odour when struck; and the colour, being of organic origin, is discharged on calcination.
British limestones of Mesozoic and Tertiary age are not gen erally compact enough to be used as marbles, but some of the shelly beds are employed to a limited extent for decorative pur poses. The most important Mesozoic marbles are the shelly lime stones of the Purbeck formation, which were a favourite material with mediaeval architects for slender clustered columns and sepul chral monuments. It consists of a mass of the shells of a fresh water snail, Paludina carinifera, embedded in a blue, grey or greenish limestone, and is found in the Upper Purbeck beds of Swanage. Excellent examples of its use may be seen in West minster Abbey and in the Temple Church, as well as in the cathe drals of Salisbury, Winchester, Worcester and Lincoln. Sussex marble is very similar, occurring in thin beds in the Weald clay and consisting largely of the shells of Paludina, principally P. sussexiensis and P. fluvioruns. The altar stones and the episcopal chair in the cathedral at Canterbury are made of this mate rial.
America possesses some valu able deposits which, in the eastern States, have been extensively worked. The crystalline limestones of western New England fur nish an abundance of white and grey marble, while a beautiful material fit for statuary has been quarried near Rutland, Vt. A grey bird's-eye marble is obtained from central New York, and the greyish clouded limestones of Thomaston, Me., have been extensively quarried. Of the variegated and coloured marbles, perhaps the most beautiful are those from the northern part of Vermont, in the neighbourhood of lake Champlain. A fine brec ciated marble is found on the Maryland side of the Potomac, below Point of Rocks. Among the principal localities for black marble may be mentioned Shoreham, Vt., and Glens Falls, N.Y. In 1937 the production of dimension marble in the United States was valued at $5,134,721, of which $3,336,545 was building marble and $1,798,176 monumental marble. Production by leading States in 1937 was Vermont, $1,539,571; Tennessee, $1,384,961; Georgia, $1,030,407 ; Missouri,
; Alabama, $313,663 ; Arkansas, $22,902; all other States, $398,203.