266 GNEISS. 



satisfactorily ascertained ; but I am induced to 

 give it a place here, in an appendix, from its 

 foliated structure and general characters. To 

 whatever family it may belong, it appears, at any 

 rate, to have no claim to a separate place as a dis- 

 tinet geological formation. 



It is a compound of quartz, schorl, mica, and 

 lithomarga, or of quartz, schorl, and lithomarga, 

 containing topazes imbedded. 



