1914 — 15] Fj eldby giringen mellem Sørfjorden og Samnanger! jorden. 231 



The Grey Granite 



(Pages 100—104). 



attracts our attention through its striking want of vegetation. 

 South of our map it may be followed along the east side of Samn- 

 angerfjorden and further aeross to the Os-district in the Bergen 

 peninsula, where it is previously described by Reusch as quartz- 

 eye-gneiss. In the Samnanger-area where Reusch also found it. 

 he gave it the name of the "grey-gneiss". That it is of eruptive 

 origin seems certain, for, as may be seen from the map, it ents 

 the polymict conglomerate, which also on the border towards the 

 grey granite is more metamorphosed than elsewhere. (Fig. 38.) 

 In the compressed granite are found fragments both of green- 

 schists and, although rather seldom, of conglomerates. 



The rock is rather pressed; under the microscope some types 

 show larger lense-shapecl aggregrates of quartz, in others the felspar 

 and its metamorphosed products are arranged in almost parallel 

 streaks with interjacent thin lenses of quartz; other types again 

 are constituted by a tine detritus. 



The mineralogical composition of the rock is the following: 



Magnetite in single small grains. 



Garnet, partly altered into chlorite. 



Biotite in small Mia. 



The felspars are so strongly compressed that they are difficult 

 to determine; they seem, however, in most instances to be plagio- 

 clase. In the metamorphosed felspar-aggregates are found numerous 

 individuals of zoisite, epidote and some albite, which also give 

 evidence of the fact that plagioclase was the original felspar. Also 

 the quartz-eye-gneiss by Os is rich in plagioclase, and it is 

 generally that sort of granite rich in plagioclase which so often 

 occurs together with the saussurite-gabbros in the old Norwegian 

 mountain-range. 



Quartz differs from the felspars through its want of meta- 

 morphic products. 



