Tunnel of the Tavistock Canal. 149 



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 Croivndale, 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 under- 

 taking 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 cop- 

 per 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, &c. 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 as- 

 suming an importance they had never before attained, and their 

 prospects were such as to encourage fresh adventures, the pro- 

 prietors of the principal ones were led to think of the scheme of 

 driving a tunnel through the hill, which is the subject of the pre- 

 sent remarks. The chief inducements were, that Morwel Down 



Vol. iv. v 



