1856.] TAYLER CRYOLITE. 143 



folia of the partly decomposed iron-ore, appearing as if it had run 

 into it in a state of solution. To this quartz- and felspar-rock suc- 

 ceeds more granitic gneiss, in which the cryolite occurs ; this gneiss 

 gradually loses its granitic character as it approaches the eastern 

 trap-vein, where it again takes on the same slaty appearance as at 

 the western trap-vein. 



We will nowrefer to the transverse section of the cryolite (fig. 2). The 

 cryolite forms a bed or vein parallel to the strata, and is about 80 feet 

 thick and 300 feet long ; it dips to the south, at an angle of nearly 45°, 

 'and runs nearly E. and W. In the upper wall of gneiss, about 2 feet 

 above its junction with the cryolite, runs a vein of sparry iron, with 

 the same dip as the cryolite ; and a layer of opake quartz-crystals lines 

 the under side of the gneiss, between the iron-ore and the cryolite : 

 sometimes sinking several feet into the cryolite, but never rising into 

 the gneiss, is a vein of argentiferous galena, containing 83 J per cent, 

 of lead, and 45 ounces of silver in the ton of ore ; this was worked 

 during the year 1854-5, and some good ore was extracted. The 

 cryolite below this vein is impregnated for a few feet with galena, 

 copper-pyrites, and sparry iron-ore ; but beyond, until within a few 

 feet from the under wall of gneiss, it is quite pure and white ; within 

 10 feet, however, of this under-gneiss, it again contains the same 

 minerals disseminated, but is here separated from the gneiss by a 

 vein of dark purple fluor-spar. The gneiss on both sides of the 

 cryolite contains much fluor-spar disseminated. 



The upper part of the cryolite at its junction with the gneiss is 

 much decomposed, leaving many cavities, which contain loose crystals 

 of sparry iron. At a depth of about 1 feet from the surface, the 

 cryolite, although free from foreign matter, assumes a darker colour ; 

 and at 15 feet it is nearly black, and more translucent and compact ; 

 and, as the deeper we sunk we found the cryolite become darker, 

 there is reason to believe that below this depth the mineral will be 

 found to be wholly black. As the white cryolite is only found at the 

 surface, and bears evidence of partial disintegration by having lost 

 some of its compactness and translucency, it is reasonable to suppose 

 that the cryolite was originally wholly dark-coloured or black. 



When the black cryolite is heated to redness, it loses about 1 per 

 cent, (moisture and acid), the whole of its colour, and part of its 

 translucency, becoming perfectly white, like the cryolite at the sur- 

 face. And from this fact we may conclude that the white colour of 

 the cryolite at the surface has been produced by a similar cause. 

 I consider it probable that the trap now found at each end of 

 the cryolite has formerly overlain it, heating it superficially, and 

 rendering it white ; there are at present no remains of overlying trap 

 between these two veins, but in this country the trap and allied rocks 

 disintegrate most rapidly from the effects of frost. The cryolite itself 

 has considerably decreased, from this and other causes ; for I found 

 a piece of it imbedded in the upper gneiss, more than 8 feet above 

 the highest part of the cryolite, proving that it formerly stood at 

 that height. 



In working the lead-vein, we sunk about 30 feet on the dip of the 



L 2 



