on the Materials used in the city of Rome. 45 



porphyreticis plateas in Palatio," Lamprid.) ; and Sir William 

 Gell has found the true green prophyry in abundance near 

 Sparta. It is universally known in Italy under the name of 

 serpentine, though quite unconnected with the serpentine of 

 mineralogists. It is a very compact felspar porphyry. The co- 

 lour of the crystals approaches mountain green set in a much 

 darker ground, which is between grass green and blackish 

 green. I have, however, a specimen from the ancient city of 

 Ostium, in which the ground is so much mixed with brown as 

 to be of a light dusky colour. It is found in Rome in consi- 

 derable abundance. Some parts of lanes, &c. are entirely paved 

 with it, but it is never seen in considerable masses. I do not 

 recollect ever seeing the smallest pillar made of it. In the bap- 

 tistery of St John Lateran two small red porphyry columns 

 have capitals of the green variety. It was much used, as we 

 have already noticed, for Mosaic pavements, particularly in 

 churches, &c. about the time of Constantine. The red species 

 of porphyry was the only one known under that name to the 

 ancients, and, in fact, gave rise to it from its purple colour. It 

 is excessively hard, and was not introduced in Rome till a late 

 period, but afterwards became so common that it obtained the 

 name of Pietra Romana peculiarly. It was sometimes used in 

 statuary, as may be seen in the Dacian captives at the Pitti 

 Palace, Florence, and in other instances, but was more gene- 

 rally used for sepulchral urns, sarcophagi, &c. Of the latter 

 we have two superb examples in the Vatican, taken from the 

 tombs of Helena and Constantia. The latter has figures, (though 

 in bad taste) executed upon it in surprising relief. But the 

 most superb specimen of this stone is the Tazza or flat basin 

 in the Vatican Museum, hewn out of one piece, and measuring 

 forty-six feet in circumference. The basis or ground of por- 

 phyry is a mixture of much red, a little blue, and a considerable 

 portion of brown ; in short, nearly what is termed cherry-red 

 by mineralogists. The crystals have a faint tint of the same 

 colour passing almost into white. Ferber divides the porphy- 

 ries into many subspecies and varieties with which I am not 

 acquainted, and must be very rare. He properly considers the 

 serpentine of Italy as a green porphyry. I may mention by 

 the way, that I have seen a large boulder stone of this substance 



