X M. Brongniart's Table 



Genus 2. WITH A BASE OF MICA. 



Species 1. GNEISS. 



Essentially composed of an abundance of mica in plates, 



and of lamellar or granular felspar, — the structure laminated. 



Obser. As there are rocks named gneiss by all geologists, which do 

 not contain quartz, thi» mineral cannot be termed an essential constituent 

 part. 



Principal varieties. 



CoMMOJf Gn Little or no quartz, 



QnARTZOSE Gn Quartz abundant. 



(Todstein in Saxony, — Huttenberg, Hartz,J' 

 Talcose Gn Granular felspar, shining and talcose mica. 



(Saint Bel, near Lyon.) 

 PoRPHYRiTic Gn Crystals of felspar disseminated in gneiss. 



(Kringeln, in Norway (von Buck.) Cevin in 



the Tarentaise.) 



Species 2. MICASCHISTE. (Mica Slate.) 



Essentially composed of an abundance of continuous mica 

 and quartz. The structure slaty. 



Principal varieties. 



QnARTZOSE M Very abundant quartz and mica, nearly alone, 



and alternating in undulating laminae. 



Granitic M Garnets nearly equally disseminated. 



Felspathic M Grains of felspar nearly equally disseminated. 



(Herold, near Ehrenfriedersdorf in Saxony.) 



Genus 3. WITH A BASE OF SCHIST. 



Species 1. PHYLLADE. (A name given in concert with 

 Messrs. Brochant and D'Jubuisson.) Mixed thonschiefer 

 of the German mineralogists. DiflFerent schists. 



Base of clay-slate containing disseminated mica, quartz, 

 felspar, hornblende, chiastolite, &c. either separately or to- 

 gether. The structure slaty. 



