Another species is the bianco e nero antico, the Marmor Proconnesium of antiquity, obtained from the celebrated quarries of Proconnesos, an island in the western part of the Propontis.  Many of the towns of Greece were decorated with this marble.  The internal part of the famous sepulchre erected by Artemisia, the widow of Mausolus, king of Caria, to her husband, and after whom all grand tombs ever since have received the name of mausoleum, was built of this marble.  So celebrated were the quarries of Proconnesos that the ancient name of the island was changed to Marmora, and the whole of the Propontis is now called the Sea of Marmora.  Although so highly esteemed in Greece, this marble does not seem to have been extensively used in Rome; the finest relics being the four columns supporting the marble canopy, in the form of a Gothic temple, which surmounts the high altar of St. Caecilia, which is among the most ancient of all the churches of Rome.  They were probably derived from some old Roman palace, and are remarkable for the clearness and brilliancy of the white blotches on a black ground.  There are different varieties of this marble:  one kind in which the blotches or veins are pure black on a pure white ground, and another in which the blotches or veins are pure white on a black ground.  In these varieties, however, the black and the white are more confused together, but remain notwithstanding distinct and separate, so that if the veins are white the ground is sure to be black, and vice versa.  The ancient Marmor Rhodium, or the giallo e nero, had golden-coloured veins on a black ground, and, owing to its compact texture, was capable of receiving a high polish.  It is very like the celebrated marble of Portovenere, a modern Italian species obtained from the western hills of the Gulf of Spezia, where the formation passes into that of the ammonitiferous limestones of the Lias and of the palaeozoic rocks.  A beautiful highly-polished specimen of Rhodian marble exists in the mask in front of the tomb of Paul III. in the tribune of St. Peter’s, sculptured by Della Porta in 1547, long previous to the discovery of the quarries of Portovenere.  It may be remarked that the grain of the latter species is such that it will not keep its polish without extreme care; a circumstance which distinguishes it from the Rhodian marble, whose tenacity in this respect renders it eminently adapted for the more costly class of decorative works.

The marbles we have been hitherto considering belong to the older calcareous formations of Italy, Greece, Asia Minor, and Egypt, and go down to the upper triassic and muschel-kalk limestones, and perhaps even to those of an older period.  But there is a class of ancient marbles in Rome of much more recent geological origin—­belonging indeed to the Miocene epoch—­which are called Lumachella, from the Italian word signifying snail, on account of the presence in all the species of fossil