on the Materials used in the City of Rome. 47 



same as a species of basalt, under the title of " Basaltes niger- 

 rimus maculis ex hornblende viridescenti ;" and the Italian 

 " Pietra d'Egitto, Pietra Nefritica." He has, however, most 

 probably made some confusion. We have only a word or two 

 to say on the granites. 



Ferber is wrong in saying that the oriental granite in no re- 

 spect differs from that of the Alps. It is in fact a sienite, 

 which contains hornblende in place of mica, as is universally 

 the case in the granites of Egypt, and consequently all the 

 obelisks and other monuments at Rome. The granite of 

 Switzerland contains talc or chlorite instead of mica, and is 

 named Protogene. I have in my possession a curious speci- 

 men from Rome, which contains abundance of quartz, appa- 

 rently no felspar, with hornblende, chlorite, and mica. This 

 is probably the " granito Nero e bianco." There are two other 

 species, the only ones mentioned by Nibby, the red and the 

 gray. The first was used for obelisks, and is most abundant. 

 The largest obelisk in Rome is that at St John Lateran, of 

 which the single shaft measures 109 feet. Eight most superb 

 columns of this granite decorate the Church of S. Maria Degli 

 Angeli, in the Baths of Dioclesian, which, enormous as they 

 are, have part of their bases buried under the pavement. The 

 gray granite was likewise much esteemed. We have fine 

 specimens of it in the broken pillars of the Temple of Venus 

 at Rome ; and the portico of the Pantheon is composed partly 

 of this, partly of the former species. When small-grained, the 

 Italians call it granitello. Ferber mentions a green granite 

 with which I am quite unacquainted. He seems to intimate 

 that it contains crystals of hornblende in a pale green basis. 

 The only true green granite now known comes from Siberia, 

 having the felspar verdigris green, (of that variety called Ama- 

 zon stone,) and it would be singular if a similar species was 

 known to the ancients. Had he not been so particular in de- 

 scribing the aspect of it, (Travels, fyc. p, 229,J we might 

 have suspected it to be the granito di gabbro of the Italians, 

 or Diallage rock. 



I have now, Sir, finished the survey I proposed to lay be- 

 fore you of this extensive and interesting subject. I have been 



