192 Proceedings of the Royal Physical Society, 



and the brecciated mass thus formed has been subsequently 

 recemented with crystalline quartz containing grains and 

 crystals of copper pyrites, zincblende, and galena. 



From the fault to the top of the burn — a distance of nearly 

 a mile— the section is, as before, a continuously descending 

 one. The series which dips S.E. at an average inclina- 

 tion of 30° is composed of white and slightly ferruginous 

 quartzites, with a few lenticular bands of mica schist. One 

 small vein of barytes crosses the burn obliquely near the top, 

 and is in turn intersected by two veins of blind quartz 

 exposed in the bed of the stream. A few yards below the 

 old dam, through which the stream flows, a basalt (dolerite) 

 dyke appears on the bank, and seems to be a continuation 

 of that on the southern side of the hill above the mines. 



The " Quartz reef " or " Mother vein " of the old miners 

 here crosses the stream and forms part of the dam wall. 

 It runs N.N.E. and S.S.W., and appears to be vertical. 

 Protruding through the brown peat and heather of Meall 

 Odhar, the band of white quartz forms a well-marked feature 

 along the southern shoulder of the hill. The outcrop is con- 

 tinuous for a distance of a mile and a quarter between the 

 old dam and the northern branch of the Allt Eas Anie. The 

 average thickness of the reef is 20 feet, and throughout its 

 entire length is composed of unmetalliferous white quartz. 



The chief workings of the Tyndrum mine are in the northern 

 side of the Sron nan Golan. Bare of vegetation and drift, the 

 rock surface is obscured only by occasional patches of d4lris 

 from the various levels, and the geological structure is at 

 once apparent. It is identical with that exposed in the Allt 

 nan Sae which we have already noticed. The workings are 

 bounded on the east by a deep ravine, through which runs 

 the fault separating the hard quartzites from the less durable 

 schists. The east side of the gully is composed of beds of a 

 soft, greenish, spotted, mica schist, considerably corrugated 

 and contorted. The schists dip from S. 20° W. to S. 10° E., 

 and thus strike obliquely against the fault, while the quartzites, 

 with a S. 50° E. dip, strike almost parallel to the line of dis- 

 location. The quartzites, which are here very hard, have a 

 dull brown or grey hue, and occur in beds separated by 



