walls of this “ecclesiastical sea-cave.”  Indeed all the outside and inside walls of the glorious old church are cased with this marble—­in the interior up to the height of the capitals of the columns; while above that, every part of the vaults and domes is incrusted with a truly Byzantine profusion of gold mosaics—­fit image, as Ruskin beautifully says, of the sea on which, like a halcyon’s nest, Venice rests, and of the glowing golden sky that shines above it.  Line after line of pleasant undulation ripples on the smooth polished marble as the sea ebbs and flows through the narrow streets of the city.  In the churches and palaces of Rome specimens of all the varieties of cipollino may be found, taken from the old ruins, for the marble is not now worked in the ancient quarries.  The largest masses of the common kind in Rome are the eight grand old Corinthian columns which form the portico of the Temple of Antoninus Pius and Faustina in the Forum.  The height of each shaft, which is composed of a single block, is forty-six feet, and the circumference fifteen feet.  The pillars look very rusty and weather-worn, and are much battered with the ill-usage which they have received.

One of the most beautiful and highly-prized marbles of ancient Rome was the species which is familiar to every visitor under the name of Giallo antico.  It must have existed in immense quantities in the time of the emperors, for fragments of it are found almost everywhere, and it is the variety that is most frequently picked up and converted into ornamental articles.  It is easily recognised by its deep brownish-yellow colour, resembling somewhat the yellow marbles of Siena and Verona, though invariably richer and brighter.  All the varieties are traversed more or less by veins and blotches of a darker yellow or brownish hue, which give them a charming variety.  The texture is remarkably fine and close-grained.  In this respect giallo antico can be distinguished from every other marble by the touch.  When polished it is exquisitely smooth and soft, looking like ivory that has become yellow with age.  No fitter material could be employed for the internal pavements or pillars of old temples, presenting a venerable appearance, as if the suns of many centuries had stained it with their own golden hue.  From the fact that it was called by the Romans Marmor Numidicum, we are led to infer that this marble was quarried in Numidia, and was brought into Rome when the region was made a Roman province by Julius Caesar.  It was probably known to the Romans in the time of Jugurtha; but the age of luxury had not then begun, and Marius and Sulla were more intent upon the glories of war than upon the arts of peace.  The quarries on the slopes of the Atlas, worked for three hundred years to supply the enormous demand made by the luxury of the masters of the world, were at last supposed to be exhausted; and the idea has long prevailed that the marble could only be found among the ruins of the Imperial City.