206 Proceedings of the Royal Physical Society. 



nomdjansk/' and which is defined as consisting of " inclusions 

 of pyrites — iron, magnetic, and copper pjrrites, erubescite, etc., 

 more rarely other sulphides as galena, blende, fahlerz, etc. — 

 in massive rocks usually in diorite, gabbro, and olivine 

 rock (serpentine)." This definition does not fit exactly as 

 the description we have given shows, for (1) the rock in 

 which most of the ore occurs is not a diorite, gabbro, or olivine 

 rock, and (2) although pyrites is most abundant, a large 

 quantity of fahlerz or grey copper is also present, but 

 magnetic iron or erubescite are not known to occur. The 

 ore, as has been remarked, occurs at places where the granitic 

 rock is decomposed, and at or near the contact with the basic 

 rock. The metallic elements have probably been originally 

 brought in by the later eruptive rock, as Thost remarks, and 

 the ore, like the chrome iron in the serpentine,. has been pro- 

 duced as a decomposition product, and along with it calcite, 

 quartz, spathic iron, and a little barytes, all of which could 

 have been derived from the minerals in the surrounding 

 rock. The dark rock is not generally so much decomposed 

 as the red, and at many places appears quite fresh, but the 

 latter is very rarely to be seen without some traces of decom- 

 position {vide V. Groddeck, §§ 80, 81). 



IV. — CoRRiE Bui. 



Argentiferous galena veins have been worked at Corrie Bui 

 on the top of Meal na Creige, a hill 2683 feet in height, situated 

 about 2 J miles S.E. of Ardeonaig, and 2 J miles S.S.E. of 

 Tomnadashan. The hill is capped by a zone of calcareous 

 schists, through which the veins run in two directions. One 

 system contains 3 veins which run E. and W., and are nearly 

 barren, but all the metalliferous veins have a N. and S. trend, 

 and a steep easterly hade. Thost states that 18 such veins 

 were crossed in a distance of 200 yards, and he had no doubt 

 that others remained undiscovered below the turf. 



The veins are of quartz varying in thickness from 4 inches 

 to 3 feet. Spathic ironstone is also abundant, and decomposes 

 into brown gossan by which the outcrop can easily be recognised. 



Copper and iron pyrites and zincblende are rare, and the 

 galena is thus comparatively pure. It is very valuable, as it 



