Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/159



The most important of these mines are Wheal Friendship, in the parish of Mary Tavy; Gunnis Lake and Drake Walls mines, in Calstock, on the Cornish side of the Tamar; Wheal Crowndale, on the banks of the Tavy, below Tavistock; Beeralstone mines, in the parish of Beer; Wheal Betsey, in Mary Tavy; Wheal Crebor, at the foot of Morwel Down, discovered in consequence of the undertaking about to be described, and some others of inferior note.

I am not able to state any account of the produce either of Gunnis Lake copper mine, which has been very considerable, or of the Beeralstone mines, but exclusive of these the others have returned since the year 1805, from 3 to 4000 tons of copper ore annually, and the quantity now raising is at the rate of at least 5000 tons in the year. There has likewise been a considerable quantity of lead raised at Wheal Betsey, and of tin at Drake Walls.

All the lodes that have been worked, are in killas, excepting that at Gunnis Lake, where the copper is found in granite. The ores of this mine differ very much from those of the other mines; those of the latter are almost entirely copper pyrites or yellow copper ore, varying in their proportions of metal from 5 to 15 per cent. while in the former mine are found besides the yellow copper ore, carbonates of copper, grey copper ore, arseniates, &cc. This fact is the more striking, as the vein is certainly the same as that worked at Wheal Crowndale and Wheal Crebor, where it traverses the killas, and at Gunnis Lake passes into granite.

About the year 1802, when the mines of this district were assuming an importance they had never before attained, and their prospects were such as to encourage fresh adventures, the proprietors of the principal ones were led to think of the scheme of driving a tunnel through the hill, which is the subject of the present remarks. The chief inducements were, that Morwel Down