MODE IV. FELSITE. 161 



perly introduced by Mr. Kirwan ; as a distinc- 

 tion between it and keralite seems first to have 

 arisen from an accurate examination of the 

 beautiful blue granite, discovered near Krieglach 

 in Stiria, where it occupies the place of common 

 felspar. The distinction, which is thus recent, 

 forms an important step in the knowledge of 

 rocks. 



Wallerius sent a specimen of his petrosilex to 

 France, which I saw in the possession of Haiiy, 

 being rose-coloured compact felspar, from Sal- 

 berg. Saussure mentions a grey felsite, explored 

 like slates near Martigny, in the valley of the 

 Rhone; and the celebrated cascade of Pisse 

 Vache falls from a rock of this kind*. His jad 

 is also now called compact felspar. Patrinf saw 

 in Siberia, near the celebrated silver-mine of 

 Zmeof, a mountain with singular natural forti- 

 fications, composed of felsite. They rise about 

 200 feet above the body of the mountain ; being 



* 1046. Between Martigny and St. Maurice there is also a sin- 

 gular variety of rocks. Among them is a kind of petrosilex, grey, 

 hard, and sonorous, with a little transparency, which rises in thin 

 plates, perfectly flat and regular : hence it is used as a slate-quarry. 

 It is probably of the same nature with patrinite, or laminar felsite. 

 The rock of the famous cascade called Pisse Vache, seems of the 

 same kind, but approaching nearer to a feljad, greenish, and semi- 

 transparent. It melts like a felsite, but with greater difficulty. 



f i. 134. 



VOL. I. M 



