51 & DOMAIN XII. VOLCANIC. 



the ejected granite contains garnets, they are com- 

 monly vitrified. 



Saussure observed, 730, the effects of vitri- 

 fication on granites in the lime-kilns of Chamouni. 

 Those that have suffered the least heat, are known 

 fry the dull white appearance, and cracks of the 

 quartz and felspar, and by the glossy golden 

 lustre of the mica. In a greater degree of heat, 

 the mica and felspar appear melted, but without 

 derangement. In the greatest heat, the mica is 

 melted into large round bubbles, while the felspar 

 looks like glass with microscopic bubbles; and 

 the quartz is only of a dull white, without any 

 appearance of fusion. 



HYPONOME III. MICA-SLATE. 



This sometimes accompanies ejected granites, 



HYPONOME IV. SLATE. 



Thi$ substance is chiefly conspicuous among 

 the ejections of Hecla. 



HYPONOME V. BASALTON. 

 HYPONOME VI. PORPHYRY. 



These two kindred rocks are frequent in vol- 

 canic countries ; and abound among the ejections 

 of New Spain, and other volcanic regions. 



