Oh. V.] PRIMARY SCHISTOSE ROCKS. 75 



single folia, as in granite : and it contains beds of hornblende, 

 limestone, and ores.* 



This gneiss, like the primary rocks already described, is 

 constantly changing its appearance, according to the propor- 

 tion and the nature of its constituent parts, which are com- 

 monly felspar, quartz, and mica. 



Around Kongsvold the gneiss is fine, slaty, with detached 

 folia of mica, which lie parallel to each other. This is near 

 the mica slate ; but, farther down, in the Straits of Drivstuen, 

 rocks of a most beautiful gneiss are to be seen, containing 

 large, and generally twin, crystals of white felspar, which 

 shine forth in the midst of thick scaly mica. The felspar 

 crystals are very much heaped together, sometimes the size of 

 the hand : the inica is shining and easily separated : all the 

 ingredients are distinct and determinate, f 



In the straits of the Figa Valley, the gneiss appears in 

 great rocks by the road-side , the mica of which is black and 

 scaly, and the felspar distinct. It contains beds of a coal- 

 black colour, which seem, in fact, to have been taken for coal, 

 for they have evidently been worked ; but they are entirely 

 composed of pure, thick, scaly, and shining mica : this mineral, 

 in isolated masses, is not unfrequent in the gneiss ; but it is a 

 singular circumstance to find it in whole beds. 



This gneiss frequently contains hornblende, and even alter- 

 nates with hornblende rocks. At Morstue, gneiss is the pre- 

 dominating rock, containing here and there subordinate beds 

 of hornblende rocks : but, through the Mordskov to the 

 eastern bank of the Miosen, the latter gradually increase in 

 quantity, till the gneiss, with white felspar and a great deal 

 of mica, only occurs as beds ; and, at last, black hornblende 

 and white felspar, in a fine granular mixture, entirely prevail. 

 " This sort of alternation of beds," says Von Buch, " which 

 gradually appear more and more frequently, is quite usual 

 when one rock takes the place of another : thus, mica slate is 



* Travels through Norway and Lapland, p. 21. f Idem, p. 102. 



