330 Notices and Extracts from the Minutes of the Geological Society. 



number of fragments of a rock, which is, as far as I can learn, entirely new, 

 among those employed by the ancients. I have inquired of several of the 

 principal lapidaries of Rome, and they all say that they never saw or heard 

 of it before, as found among ancient ruins. This rock is green granite ; that 

 is to say, granite, the felspar of which is of a green colour, and exactly resem- 

 bling that which is commonly called Amazonian stone. The fragments which 

 I have found have been generally small, and some very small ; the largest 

 is about the size of a small melon. 1 have consulted the only two mineralogical 

 works which I have with me, "Allan's Synonymes," and " Jameson's System 

 of Mineralogy." In the former, Siberia is the only locality mentioned for 

 green felspar. Jameson (2nd edition, vol. i. pages 375, 376.) states that it is 

 found in a vein in granite, in the government of Ubinsky, in the Uralian 

 mountains ; also in contemporaneous masses in the granite of Onega ; and 

 further, that it is found in small rolletl pieces on the banks of the river of 

 Amazons. It would be interesting to know from whence the ancients derived 

 it ; as its two Siberian localities must have been little more accessible than that 

 in the undiscovered continent of America. In endeavouring to ascertain this 

 point, we are not entirely without a glimmering of light, as on some of these 

 fragments, which show their original surface, there are Egyptian hierogly- 

 phics. This circumstance induces me to suppose that green granite must 

 have been found, though as a very rare substance, in Egypt. What these 

 masses were, when the villa of Vopiscus was standing, it is useless to inquire ; 

 and perhaps future excavations may settle that point. By the largest mass 

 which I had the good fortune to find, it appears that quartz was the principal 

 constituent of the green granite ; the felspar was however pretty abundant, 

 and the mica disseminated in very small proportions, and of a black colour. In 

 one fragment are some appearances of black acicular crystals in the quartz, 

 probably either hornblende, or tourmaline. 



Accompanying this letter, I send five specimens ; — one, of which I have 

 liad a surface polished, will you be so kind as to give in my name to the 



(Jeological Society ? I also send for the Geological Society a small 



specimen of a decomposing red slaty mineral, which I found in my excava- 

 tion, and with which I am unacquainted. It appears to have formed part of 

 a cornice. 



Believe me, my dear Sir, 



Yours very truly, 



COMPTON. 



Rome, May 20th, 1825. 



