ORIGIN AND DEVELOPMENT OP ORE-DEPOSITS. 133 



of stuff were stamped. The " overburden " gave 5 lbs. to the 

 ton, the granite about as much, and the elvan 12 lbs. during 

 these trials, which just paid expenses but no more, on a scale of 

 20 to 30 tons per day. 



The total quantity of elvan removed in this class of stock- 

 work may perhaps be reasonably estimated at one million tons, 

 and the average produce at one-half per cent., or say 4,500 

 tons in all. 



6. — COPPER STOCKWORES IN KILLAS. 



These are rare in Cornwall, but there are the remains of 

 several to be seen along the north coast to the west of St. Agnes. 



Wheal Music. This mine is situated about 2 miles to the 

 north of Scorrier station, and it has not, I believe, been worked 

 for about 60 years. Mr. Henwood states that it was worked on 

 well-known lodes for many years, and that at length these were 

 up split into minute strings and branches, none of which were 

 singly worth pursuit. The whole rock was then removed and the 

 copper ores extracted. An excavation of an elliptical form of 

 about an acre in area, and 25 fathoms in depth, yet stands open to 

 the day. About four millions of cubic feet must have been 

 removed. It closely resembles the net- work of the tin veins in 

 granite at Carclaze."* The copper it appears was mainly in 

 the form of copper-pyrites, but this was often converted 

 superficially into malachite ; the country rock was tourmaline- 

 schist of a bluish grey tinge. f 



Copper disseminated in an ancient conglomerate occurs in the 

 form of copper-pyrites, at Bellurian Cove,;}: and native copper 

 was found disseminated in the serpentine at Wheal Trenance, in 

 the same parish of Mullion ; a fine mass from this place may 

 now be seen in the Museum of Practical Geology in London. 

 Writing of this place in 1818, Mr. Ashurst Majendie says "The 

 mines of copper have been discontinued. I was informed that 

 at low water in spring tides, narrow veins of native copper may 

 be observed in the serpentine, where it is covered by the sea. § 



* Trans. Roy. Geol. Soc, Corn., v, 98, note. 



t Ibid, p. 98 and 235. 



X Delabeche, Eeport, &c.. p. 31, note. 



§ Trans. Roy. Geol Soc , Corn., i, p. 33. 



