OUTLINES OF GEOLOGY. 



63 



V, INFERIOR ORDER, 



151. The inferior order is composed of two groups — that 

 in which the siatey structure predominates, and that in which, 

 although still stratified, the formation by crystallization is 

 the most obvious character. Among the siatey rocks, no 

 others need be cited than those enumerated in the last group 

 of the foregoing order. 



The crystaline stratified rocks are : 



Gneiss, a rock composed of felspar, mica, and quartz, and 

 therefore identical in composition with granite, from which it 

 differs by its stratified formation ; 



Hyalomicte, which differs from gneiss, in wanting "the 

 felspar ; 



Mica slate, which contains but little quartz, and is some- 

 times wholly composed of mica; 



Eurite, wholly composed of compact or granular felspar ; 

 Hornblende slate ; 

 Quartz slate ; 



Siderocrist, made up of specular oxide of iron and mica ; 

 Magnetic oxide of Jron ; 



Granular Carbonate of Lime, from the coarsest grains, 

 whence perfect crystals may be separated, to saccharoid ; 

 Granular dolomite ; 



Protogine, a rock composed of talc and felspar. 



The siderocrist often contains native gold in small parti- 

 cles, and has been suspected to be the original site of the 

 diamond. 



Pyrites is often imbedded in the rocks of this formation, 

 and sometimes forms one of its rocks. In the latter case it 

 is occasionally rich in gold. 



