MODE V. PORPHYRY. 83 



1539. B. " Green porphyry. The cement of 

 this porphyry approaches likewise to that of the 

 ophite *; its colour is however less beautiful : it 

 is a green which verges to the deep grey : it like- 

 wise assumes a surface less uniform and less soft 

 to the touch. In other respects its fracture and 

 hardness are the same, but it is a little more re- 

 fractory, and the glass it yields is less hard and 

 opake. The small fragments of this glass ars 

 however attracted by the magnet. 



" The crystals of felspar which this porphyry 

 contains are, as in the ophite, lengthened oblique 

 angled prisms, of a white inclining a little to green; 

 of an unctuous and milky lustre ; their fracture is 

 more compact, and presents thicker laminae than. 

 common felspar. 



1539. C. " Red porphyry. The cement of this 

 porphyry is of what I call primitive petrosilex. 

 In the rolled pebbles its surface is pretty uniform, 

 almost soft to the touch. It breaks into irregular 

 fragments in sharpish angles, almost opake on 

 their edges. Its fracture is scaly with very thin 

 scales, which, viewed by a microscope, appear 

 semi-transparent and whitish, whilst the base is 

 of a pretty deep wine red. 



* By ophite, Saussure, like many others, erroneously understands 

 the green porphyry. 



