DOMAIN VII. COMPOSITE. 



NOME IV. PORPHYRY, WITH CHALCE- 

 DONY. 



The green porphyry, in particular, sometimes 

 appears spotted with chalcedony, so as to as- 

 sume the form of a composite rock*. Ferber, 

 it has been already observed, saw numerous 

 blocks of green porphyry at Ostia, the sea-port 

 of Rome, where they had been disembarked in 

 ancient times, and neglected after the empire 

 fell a prey to barbarians. 



NOME V. JASPER, WITH AGATE AND 

 CHALCEDONY. 



This curious rock is described, by Petrini, as 

 consisting of these three substances, in veins of 

 white, green, red, yellow, purple. It admits a 

 beautiful polish, and is found at Monte Rufole, 

 in the Volterranof. 



* In the noble collection of Besson, at Paris, there is a specimen 

 joined with pure transparent quartz, which had probably passed as 

 a vein through the rock. 



t Gabinetto Nazareno, Roma 1792, 2 vols. 8vo. ii. 258. 



