214 DOMAIN II. SILICEOUS. 



Primitive lime-stone likewise alternates with 

 granite, and has even been found to assume the 

 granitic forms. The alternation of porphyry 

 with granite is of general observation in all pri- 

 mitive mountains. 



F metSlig in Gneiss also frequently contains garnets, acti- 

 note, magnetic iron, and pyrites. It is, after 

 clay-slate, the most metalliferous of all rocks. 

 The chief mines of Saxony, Bohemia, and Salz- 

 burg, are situate in this rock, which, though 

 very common on the Continent, is comparatively 

 rare in Great Britain and Ireland. 



STRUCTURE I. TABULAR, OR IN THICK SCHISTOSE 

 FORMS. 



This kind is commonly derived from granite, or 

 passes into that rock. 



Tabular gneiss, from the Alps. 



The same, from the isle of Leuis, in the exte- 

 rior chain of the Hebudes, Scotland. 



STRUCTURE II. LAMINAR. 



This is the common appearance of gneiss, and 

 may be divided into two Aspects. 



Aspect 1. Plane or level. Gneiss, with red 

 felspar, from the Alps, Norway, Saxony. 



