Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/138

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Mr. William Phillips on the Veins of Cornwall.

seldom yield it of a greater price than £4 or £5 per ton. A few tons were lately sold from the United Mines at £100. The general average perhaps does not exceed about £7. 10s. or £8 per ton.

In few metalliferous veins does the ore prove so continuous, as after it has been taken away to leave a large hollow load. The intermediate spaces between the ore are mostly filled with what the miner terms deads, which consist of quartz, fluor, gossan, iron pyrites and other substances, as well as occasionally portions of the country through which the vein runs; but the walls of the vein are nevertheless generally determinable. The deads are not always a disadvantage to the miner, as they serve to keep apart the country on either side the vein; but for this purpose, when the vein has been left hollow by taking away a large body of ore, strong timbers are made use of; these are not however always found to be of strength sufficient to prevent the falling in of the cavity. An instance of this occurred in the copper mine called Huel Alfred; one of the veins of which was hollowed out for about 100 fathoms in depth, 80 fathoms in length at bottom, and 80 fathoms above, and varying in width from 9 to 24 feet. Notwithstanding great labour, skill and expense had been bestowed, and the most substantial timber employed in order to keep apart the walls of the vein, many thousands of tons came down in an instant; fortunately seventeen men who had been working in the very place on which the whole fell, had left it half an hour before the accident. The whole has been supported, and they are now working beneath it.

It has sometimes happened that in a large load, and where it is largest, the miner has suddenly arrived at a piece of dead ground in the middle of it, which in depth spreads wider so as to occupy nearly the whole of the vein, leaving on each side only a small connecting string of ore. This has been known to extend many