DOMAIN I. SIDEROUS. 



phyry to every substance in which small crystals 

 are imbedded, is as absurd as it would be to con- 

 found granular limestone with granular quartz; 

 or any other remote substances merely of similar 

 structure, or even aspect. 



STRUCTURE I. PORPHYRY WITH LARGE CRYSTALS 

 OF FELSPAR. 



Aspect 1. Red Porphyry. This kind is fre- 

 quent in ancient monuments. The crystals are 

 seldom so regular as those of the next structure. 

 It is sometimes interspersed -with globules of a 

 finer porphyry 3 or even of porphyrin. 



Porphyry, from Egypt, or the ruins of Rome. 



The same, from the Grampian Mountains in 

 Scotland. It chiefly occurs in Glenco*. 



The same, from Corsica. 



Aspect 2. Black. A fine column of this kind 

 is in the church of St. Prassede, at Rome. 



Aspect 3. Green. This has sometimes been 

 called verd-antique, but the proper verd-antique 

 is a mixture of serpentine and white marble. The 

 green porphyry has also been erroneously supposed 



* Which must not be confounded with Glen Cro, not far from 

 Inverary. 



