l()4i DOMAIN II. SILICEOUS. 



compact felspar. It is sometimes of a greenish 

 hue, from a small quantity of steatite dissolved 

 in its paste ; and sometimes grey or black, from 

 a mixture of bitumen, as Dolomieu argues, from 

 its becoming white before it melts. Felspar often 

 passes into felsite, and the latter often contains 

 little scales or crystals of the former. 



This ingenious, but prolix and discursive 

 T 7ei k sp n i! f author, distinguishes two kinds of felspar; that 

 which contains lime, and that which contains 

 magnesia. The latter is more hard and weighty, 

 and less fusible than the other; and as it ap- 

 proaches to the nature of jad, might, by a com- 

 plex term, alike useful for precision and the 

 Feijad. memory, be called feljad. Some granites present 

 both kinds, but felsite generally contains lime; 

 it is also found with crystals of schorl, plates of 

 siderite, or veins of quartz. 



According to Dolomieu, felsite forms the base 

 of several porphyries found in the valley of 

 Niolo, in Corsica. One kind is green, and as 

 fine as chalcedony, sprinkled with an infinite 

 number of red dots, being little crystals of fel- 

 spar. A brown felsite porphyry, of a schistose 

 kind, is used for slates in the village of Pergine, 

 in the bishopric of Trent. 



" The mountains of Tyrol, between Trent and 

 Bolsano, are almost entirely composed of por- 



