Joseph Carne on the Submarine Mines of the St Just District

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Joseph Carne on the Mineral Production & Geology of the Parsh of St. Just (Transactions of the Royal Geological Society of Cornwall 1822 proceedings of lecture given in 1821)
Submarine Mines

These are objects rather of curiosity than geology; but they are singular, and therefore merit a description. Mr. Hawkins has given, in the preceding volume, an account of the principal submarine mine in Cornwall, viz. the Wherry; the only one of which the entrance is actually through the sea. Many of the mines of St. Just are on the border of the land and some are on the very edge of its precipitous termination, and are wrought to a considerable distance under the sea; but all communication to them is from the land.

1 Levant Copper Mine. The first level in this mine is about 17 fathoms below high water mark, and is extended 40 fathoms in length under the sea. As the shore declines rapidly, there can be scarcely more than 10 fathoms between the end of the level and the sea. In one part of it the workmen, tempted by a bunch of copper ore, followed it to the height of five fathoms above the level, but feared to proceed further. There is a deeper level, 28 fathoms under high water mark, which has been driven 26 fathoms under the sea. Not only the roaring of the sea in stormy weather but the ordinary breaking of the waves on the beach, is distinctly heard by the miners. The water in this mine is salt; but there is so little of it that, although the depth is 42 fathoms, the whole is drawn to the adit in a bucket, by the labour of two men.

2. Tolvaen Copper Mine. The levels of this mine are known to have been extended under the sea; but as it has not been wrought since about the year 1754, I cannot obtain any particulars respecting it.

3. Huel Cock Copper Mine. This mine has not been wrought for several years; but 1 have collected the following particulars from an old miner. The mouth of the adit is very little above high water mark: at very high tides the sea flows into it. At the depth of about 20 fathoms, a level is driven nearly 100 fathoms in length under the sea: the depth of the sea at that distance from the shore I am not acquainted with; but the space between the bottom of the sea and the end of the level must be very small; perhaps not more than five fathoms. In stormy weather, the thundering noise of the sea, and, the concussion caused by the heavy waves dashing against the rocky beach, were so terrific that the affrighted workmen would sometimes fly from the spot, supposing the sea was actually breaking into it. In one part of this level the miners followed a bunch of ore about 12 fathoms above the level, and would have pursued it still farther, had not the agents seen the danger and forbidden them. About 40 fathoms under high water mark., another level is driven under the sea, about 30 fathoms in length, and, the whole of the lode between this and the higher level is taken away. At 20 fathoms deeper, or 60 fathoms in all, a third level is driven about the same distance. Even in the deepest part, the workmen could distinctly hear the noise of the waves. The water in every level was very brakish, and was drawn to the adit by a small water engine.

4. Botallack Tin and Copper Mine. This mine was wrought under the sea beyond the memory of any person now living. The ancient workmen have indeed left a convincing proof of it by having followed the ore so high as to open a communication between the sea and the mine. Whether this opening was made whilst they were at work, or the, sea afterwards broke through the thin barrier which was left, is not known; it is, however, now stopped by a wooden - platform, on which is laid a mass of slimy turf, and the whole is covered by the stony fragments of the beach. At about half spring, the sea flows over it at every return of the tide. At present, the first level on the Crown lode is about 30 fathoms below high water mark, and is driven 30 fathoms horizontally; the 40 fathoms level is driven 10 fathoms, the 65 fathoms level, 30 fathoms,-and the 85 fathoms level, 40 fathoms, all under the sea. In the highest level, the noise of a heavy sea beating against the.rocks is frequently sufficient to ternfy the workmen, and even in the deepest part it is distinctly heard. The water is brakish, but not so in the lower as in the higher levels. A singular circumstance occurs in the 40 fathoms level: a small quantity of clear fresh water oozes out at one spot, whilst all the water around it is salt. this is perhaps conveyed in a small vein of which the most penetrable part does not come in contact with the sea. On Huel Button lode, also, there are two levels at the depth of 40 and 50 fathoms below high water mark, in which the lode has been pursued under the sea; in the former about 20, and in the latter 30 fathoms in length. Although the depth of this mine is 105 fathoms below the adit, the whole of the water drawn by a small steam engine does not exceed 40 gallons per minute. Botallack mine is now become one of the Lions of Cornwall, and is an object of as much enquiry, attention, and admiration, as either the Land's End or the Logan rock; but as its singular situation and romantic appearance have been the subjects of Dr. Paris's pen in his "Guide to Mounts Bay,-" I shall not attempt to add to the effect of his description.

5. Huel Castle Copper Mine. This mine has been wrought in a very limited way. The extent which has been explored under the sea does not exceed ten fathoms, and in that space nothing, has occurred worthy of particular remark.

6. Praze Tin Mine here, at the depth of 20 fathoms under high water mark, a level has been driven about twenty fathoms in length under the sea. This mine, however, has not been wrought for more than forty years; I am therefore obliged to dismiss it with this short notice. The mines already mentioned are all in slate; and the small quantity of water which is found in them proves the superior compactness of this slate, as well as of the veins which it contains, to the killas and the veins of most other parts of Cornwall.

7. Little Bounds Tin Mine. Here three distinct lodes, distant from each other, have been wrought under the sea; two of them are in granite; the other is in slate. Here also, at some former period, through the avarice or carelessness of the workmen, a communication was made in two parts of the lode known by the name of Saveall's lode, between the sea and the mine: one of them is about high water mark at spring tides; the other is covered by the sea at every tide, except at very low neaps. great and constant attention is therefore paid to the latter, which was at first stopped by a piece of Wood covered with turf, but as this was found not to be perfectly secure, a thick platform caulked like the deck of a ship, is now placed on it, which renders it almost water proof On Little Bounds lode, the 20 fathoms level below the adit is driven 40 fathoms horizontally under the sea: the other levels to the depth of 64 fathoms are driven various lengths, from 30 to 60 fathoms. On the north lode the 40 fathoms level is driven 40 fathoms, and on Saveall's lode (in slate) the levels are extended from 1 0 to 40 fathoms under the sea. The breaking of the waves is heard in all the levels; but as a part of this mine is under a pebbly beach, the rolling of the large pebbles, in boisterous weather, causes a more terrifying noise, and a greater concussion, than are produced by the mere dashing of the waves against the rocks. The water is all brackish, and, of course, injures the pumps. It is drawn by a water engine which is erected on the very extremity of the cliff. The situation of this mine, although not quite so romantic as that of Botallack, is yet well deserving of attention. Mr. Lysons considered it worthy of an engraving in his Magna Britannia. Small quantities of tin ore are frequently thrown up by the sea, on the beach below the Little Bounds engine. One or more workmen may generally be seen, on the return of the tide after high water, searching for tin amongst the sand and shingle. It is probable that this comes from the back of some of the tin-lodes which run under the sea.

8. -Riblose Tin Mine. The lode of this mine (which is not now at work) has been pursued across a small creek near Caraglose Head. The cavities in the granite cliff, from which the upper parts of this and other lodes have probably been washed away by the sea have a very interesting appearance.

9. Huel St. Just Tin Mine is the last submarine mine which I have to notice. It is wholly in granite, and furnishes another instance of the dangerous consequences of approaching too near to the sea, whilst in pursuit of the treasures of the earth. In one part of this mine, the sea broke into the cavity from which the lode had been taken away too near to the surface. There are only two levels in this mine below high water mark; one at the depth of 17, and the other, 27 fathoms: the former has been driven 30, and the latter 35 fathoms in a horizontal direction under the sea. The water, as in the other mines, is very brackish. This mine has not been wrought for several years; but is now about to be again set at work.

I have no doubt that several other lodes in this Parish have been wrought under the sea, although, perhaps, not within the recollection of the present race of miners.
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