I know no more interesting pursuit in Rome than such an investigation; the objects, when their history is ascertained, acquiring a charm from association, over and above their own intrinsic beauty and interest. Most of the materials with which the three hundred and sixty-five churches of modern Rome have been constructed have been derived from the ruins of the ancient city. With the exception of a few comparatively insignificant portions brought from the modern quarries of Carrara, Siena, and Sicily, to complete subordinate details and to give a finish to the work, no marbles, it is said, have been used in ecclesiastical and palatial architecture for the last fifteen hundred years, save those found conveniently on the spot; and hardly a brick has been made or a stone of travertine or tufa hewn out for domestic buildings within the same period. The construction of St. Peter's itself involved more destruction of classical monuments than all the appropriations of previous and subsequent Vandals put together. Much has been lost on account of this extraordinary transmutation and reconsecration, whose loss we can never cease to deplore; but we must not forget at the same time that much has been conserved which would otherwise have wasted away under the slow ravages of time, been consigned to the lime-kiln, or disappeared in obscure and ignoble use. Enough remains to overwhelm us with astonishment, and furnish materials for the study of years. The white marbles of Greece were the first introduced into Rome. Paros supplied the earliest specimens, and long held a monopoly of the trade. _Marmor Parium_, or Marmo Greco duro, as it is called by the modern Italians, is the very flower and consummation of the rocks. This material seems to have been created specially for the use of the sculptor--as that in which he can express most clearly and beautifully his ideal conceptions; and the surpassing excellence of ancient Greek sculpture was largely due to the suitability for high art of the marble of the country, which was so stainlessly pure, delicate, and uniform--as Ruskin remarks, so soft as to allow the sculptor to work it without force, and trace on it his finest lines, and yet so hard as never to betray the touch or moulder away beneath the chisel. Parian marble is by far the most beautiful of the Greek marbles. It is a nearly pure carbonate of lime of creamy whiteness, with a finely crystalline granular structure, and is nearly translucent. It may be readily distinguished from all other white marbles by the peculiarly sparkling light that shines from its crystalline facets on being freshly broken; and this peculiarity enables the expert at once to determine the origin of any fragment of Greek or Roman statuary. The ancient quarries in the island of Paros are still wrought, though very little marble from this source is exported to other countries. In the entablature around the tomb of Caecilia Metella, which is composed of