Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/140

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Mr. William Phillips on the Veins of Cornwall.

objects of the miner is to bring home an adit to it. An adit is a water course, or rather an underground passage, about 6 feet high and 21/2 wide, and is begun at the bottom of a neighbouring valley and driven up to the vein, for the purpose of draining it of water above their point of contact. In the event also of the mine having a steam engine upon it to raise the water from a still greater depth, it is not raised by the engine to the surface, but delivered into the adit. The general level of the mining-country East and west of Redruth is, according to Dr. Berger, from 350 to 450 feet above that of the sea, except where the granite overtops the schist, as in the instances of Cam-brae, Carn-math, and some few other hills, the summits of which are at a considerably greater elevation. This general level of the country is intersected by frequent vallies, which afford great advantages for the formation of adits, and consequently for the carrying away of the water from the mines. One adit frequently serves this purpose, for 2, 3 or more mines. Pryce, who published his work, entitled Mineralogia Cornubiensis, about 30 years ago, says p. 148, ‘Though we seldom see an adit half a mile in length, there are 2 or 3 of three times that length, these are the longest I know of.’ But since his time, one has been driven through a considerable tract of country at the lowest possible depth, as its mouth or extremity is nearly on a level with the water in one of the creeks of Falmouth harbour, into which it empties; and being below all other adits in that neighbourhood, it is called the deep adit. It does not run in one course, either direct or circuitous, the whole of its way; but taking into calculation its various branchings in and through the numerous mines (those of Gwennap) which it relieves of their water, it may be said to be about 24 miles in length.

Taking into consideration the purpose of an adit, it might be presumed that it is wrought on an inclined plane from the place at