20 GEOLOGICAL MEMOIRS. 



yellow sandstone, broken through by trap ; under this a mica-schist, 

 resting on a quartzite, which was greatly disturbed by granitic erup- 

 tions ; below this a bed of hornblende-schist, attaining, in places, a 

 thickness of 300 feet ; and in its lower part containing a thin but 

 extremely characteristic bed, remarkable for the predominance of 

 silicates of alumina and magnesia, as chiastolite, andalusite, cyanite, 

 rhoetizite, iolite, aspaziolite, chlorite, &c, which rendered it at 

 once recognizable and of great service in the examination of the 

 country further west ; under this a true mica-schist, consisting of 

 quartz and mica, resting upon a quartzite, which formed the upper 

 bed of a series of six quartzites and six hornblendic schist beds 

 alternating. None of these beds, in their normal state, contained 

 felspar ; the hornblendic schists are very variable in thickness, whilst 

 the quartzites were found more constant. 



As seen from the sections accompanying these memoirs, the above 

 series of beds formed the coast-line between Langesund and Oster- 

 risoer. 



The gneiss present in the district was divided into two classes : — 



1 . A foliated granite, or an ordinary eruptive granite, in which 

 the direction of the mica-planes had caused a parallel structure to be 

 visible ; 



2. A rock formed in situ by the contact of the igneous rocks of 

 the district with the metamorphic schists above described. 



The first of these classes was well developed at Edisvand, where a 

 section alongside a lake, about fourteen miles long, showed several 

 mountains of this rock, with sides descending almost perpendicularly 

 to the water's edge, and showing large fragments of hornblende and 

 mica- schist enclosed in the granite-gneiss. These were often of im- 

 mense size, and, from their dark colour, formed a striking contrast 

 with the pinkish- white colour of the granite-gneiss. In parts the 

 gneiss loses all traces of foliated structure, thus passing insensibly 

 into an ordinary granite. At other parts the gneiss sends veins into 

 the schists, which veins presented the appearance of ordinary granite ; 

 yet the change of structure was so gradual, that no line of demar- 

 cation could be drawn between the granite and the gneiss : the 

 mineralogical character of both was the same ; and, combined with 

 the frequent occurrence of enclosed fragments of other rocks, no 

 doubt could be entertained of its true eruptive origin ; and every- 

 where the rounded and dome-shaped contour of the mountains made 

 the same impression on the observer. In this gneiss no bedding 

 was observed, only foliated structure. 



The gneiss of Ekeberg and the Christiania Fjord, as also at Fos- 

 sund, near Skien, is also considered by the author as pertaining to 

 this class. 



The second species of gneiss was very distinct from the above ; 

 and, by following out the beds, they were invariably found, sooner 

 or later, to assume the character of the original schist. When 

 greater masses of granite or diorite came in contact with the more 

 fusible beds of these schists, they were sometimes so fused in situ 

 as to be with difficulty distinguished from true igneous rocks ; thus 



