142 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 23, 



space I shall confine my remarks. The section is not drawn accu- 

 rately to a scale, but it is about ^ inch to the fathom. 



Starting from the western trap-vein, which is situated in schistose 

 gneiss and hornblende-schist, we find the gneiss gradually losing its 

 slaty structure, until in the neighbourhood of the cryolite it becomes 

 granitic, and now contains numerous metallic traces ; before arriving 

 at the cryolite, we find a wide vein of white quartz and felspar, run- 

 ning about S.W. ; the quartz and felspar are in very large masses 

 and crystals, some crystals of quartz measuring a foot in thickness. 

 This rock is traversed in several directions by small veins and masses 

 of cryolite, isolated from the larger body of that mineral, in 

 which, as well as in the rock, are to be found numerous crystals of a 

 variety of tantalite, oxide of tin, blende, molybdenum, much galena, 

 copper-pyrites, arsenical and iron-pyrites, and sparry iron-ore. In 

 this rock are many small caverns, arising from the decomposition of 

 the felspar, and probably also from the decomposition of the cryo- 

 lite, which is here porphyritic, containing crystals of felspar and 

 quartz. The floors of these caverns are covered with loose crystals 

 and fragments of felspar, and in some places kaolin, crystals of tin- 

 stone, and carbonate of iron. In one of these cavities is a large vein 

 of arsenical pyrites and purple fluor-spar ; also a large vein of black 

 cryolite, containing copper- and iron-pyrites, and red felspar. Smaller 

 cavities are found when blasting, the sides of which are completely 

 covered with crystals of the tantalite, resembling on a large scale 



Fig. 2. — Transverse Section of the Cryolite at Evigtok» 



(The width of the Cryohte is about 80 feet.) 

 S. N. 



9^9- 

 i. 



9- 

 I. 



/. 



Gneiss. 



Sparry iron-ore. 



Quarts-vein. 



Argentiferous galena. 



Purple fluor-spar. 



Black Cryolite. 

 pi, pL 



Galena, copper-pyrites, blende, 

 iron-pyrites, and carbonate of 

 iron scattered in cryolite. 



Fragment of cryolite was found 

 imbedded at this spot. 



the crystalline cavities in amygdaloidal traps. In this quartz- and 

 felspar-rock there is a remarkable vein, containing soft ferruginous 

 clay and rolled pebbles, sparry iron-ore, and copper-pyrites. The 

 copper lies over the sparry iron, and runs in fine threads between the 



