Further to my earlier posting about prehistoric caverns at Stonehouse, I heard from Ernie Stanton who told me about a publication that he'd discovered called the 'South Devon Monthly Museum'. Within its pages is an article that was published in 1796 and includes a letter to the then Lord Edgcumbe concerning the caverns. It makes very interesting reading and I've reproduced it below. It's a long-winded account of the caverns, and you might not get to the end, but it's interesting to think that all this possibly exists under Stonehouse today. From the measurements given, it would probably be possible to work out the exact position of the caverns today.
For more information about the caverns, please read my previous posting at
Here's the complete article as it appears within the publication:
The following account of an extraordinary cave discovered at Stonehouseis extracted from the 'Weekly Entertainer', for July I6th, 1796.
AN ACCOUNT OF A SUBTERRANEAN CAVERN AT STONEHOUSE, NEAR PLYMOUTH.
By the late ingenious Dr. Geach,
To the Right Hon. Lord Edgecumbe.
Plymouth-Dock, March 1st., 1776.
My Lord,
I have the honour of communicating to your lordship an account, which I took on the spot, of a subterranean cavern, lately discovered in your Lordship's demesnes at Stonehouse. The place, at a considerable extent round, as your Lordship well knows, belonged formerly to the monks : part of the wall that inclosed their garden is still to be seen. The cavern was accidentally discovered by some miners in blowing up a contiguous rock of marble. The aperture, disclosed by the explosion, was about four feet in diameter, and looked not unlike a hole bored with an auger. It was covered with a broad flat stone cemented with lime and sand ; and twelve feet above it, the ground seemed to have been made with rubbish brought thither, for what purpose I know not, unless it were for that of concealment. Here indeed, but here only, we saw some appearance of art, and vestige of masonry. The hill itself, at the northern side of which this vault was found, consists, for the most part, of lime-stone, or rather marble. From the mouth of this cave (through which we descended by a ladder) to the first base, or landing place, is twenty-six feet. At this base is an opening, bearing N. W. by W. to which we have given the name of Tent Cave. It resembles a tent at its base, and in its circumference, and stretches upwards, somewhat pyramidically, to an invisible point. It is, as far as we can measure, about ten feet high, seven broad, twenty-two long : though there is an opening, which, on account of its narrowness we could not well examine, and in all probability it has a dangerous flexure. In each side of this Tent Cave is a cleft; the right runs horizontally inwards ten feet, the left measures six by four. The sides of the cave are everywhere deeply and uncouthly indented, and here and there strengthened with ribs, naturally formed, which, placed at a due distance from each other, give some ideas of fluted pillars in old churches.
In a direct line from this cave to the opposite point is a road thirty feet long. The descent is steep and rugged, either from stones thrown into it from above, since the discovery, or from frailments that have fallen off at different times, from different places below. This road is very strongly but rudely arched over, and many holes on both sides are to be seen ; but being very narrow, do not admit of remote inspection or critical scrutiny.
Having scrambled down this deep descent, we arrive at a natural arch of Gothic-like structure, which is four feet from side to side, and six feet high. Here some petrefactions are seen depending. On the right of this arch is an opening like a funnel, into which a slender person might creep ; on the left is another correspondent funnel, the course of which is oblique, and the end unknown.
Beyond this Gothic pile is a large space, to which the arch is an entrance. This space, or inner room (for so we have termed it) is eleven feet long, ten broad twenty-five high. Its sides have many large excavations, and here two columns, which seem to be a mass of petrefactions, project considerably. On the surfaces of those pillars below, are seen some fantastic protuberances, and on the hanging roofs above, some crystal drops that have been petrified in their progress. Between those columns is a chasm capable of containing three or four men.
Returning from this room, we perceive on the left hand side, an avenue thirty feet long naturally floored with clay, and vaulted with stone. It bears S. S. W. and before we have crept through it, we see a passage of difficult access and dangerous investigation. It runs forward twenty-five feet, and opens over the vault thirty feet high near the largest well. Opposite to this passage are two caverns, both on the right hand. The first bears N. W. by W. and running forwards in a strait line about twenty feet, forms a curve that verges somewhat to the N. E. Here we walk and creep in a winding course from cell to cell, till we are stopped by a well of water, the breadth and depth of which are as yet not fully known. This winding cavern is three feet wide, in some parts five feet high, in some eight. Returning to the avenue we find adjoining to this cavern, but separated by a large and massy partition of stone, the second cavern running west ; and by descending over some small piles of lime-stone, or rather broken rocks, the bottom here being shelvy slate, or more properly a combination of slate and lime-stone, we discovered another well of water. This is the largest; the depth of it is, in one place, twenty-three feet, the width uncertain. Opposite to this well, on the left hand, by mounting over a small ridge of rocks, covered with wet and slippery clay, we enter a vault eight feet broad, eighteen long, thirty high. Here, towards the S. E., a road, not easy of ascent, runs upwards seventy-two feet towards the surface of the earth, and so near to it, that the sound of the voice, or of a mallet within, might be distinctly heard without, in consequence of which a very large opening has been made into it. At the bottom of this vault, in a place not readily observed, is another well of water, the depth of which, on account of its situation, cannot be well fathomed, nor the breadth of it ascertained.
While the miners were exploring those gloomy and grotesque regions, they were alarmed at a murmuring sound, that seemed to come from the hollows of the cave, and one of them, who chanced to be near the largest well with a candle in his hand, saw at that instant the water rise about half a foot.
This phenomenon then could not be explained ; but now we think that the several wells are nearly on a level, and that the waters shape their course towards the sea, and mix with it in Mill Bay, at the distance of four hundred and twelve feet. It is not certain whether those wells, though they lie below the extremity of the lime-stone, have a mutual communication or not : but it is highly probable, as the bottom of the largest well is clay, and its sides are shelvy slate, that there are sprinos, and it is certain that this shelvy vein of slate, nearly of the same kind and colour with some seen at Mount Edgecumbe on the opposite shore, is continued even to the sea, where two openings at low water have been found, through which it is probable the water of the great well discharges itself. When the tide rises, it is presumed that the pressure of the sea without retards the course of the water within, and this may account for the rise and fall so manifest at different times of sounding : and the same circumstance is observed also in a well near the old French prison, in the environs of Plymouth.
Each cavern has its arch, each arch is strong, and in general curious. The way to the largest well is, in one part, roofed with solid and smooth stone, not unlike the arch of an oven. No one seemed to be affected by the damps till he came hither, and then the candles grew dim, and one of the investigators, as well as myself, felt unusual and uneasy sensations.
However, since an opening has been made near the arch of the great well, and the air has had a much freer access, no such sympoms have been perceived. It is very likely that the hill itself is hollow ; some of the caverns have reciprocal communications, but the clefts are often too narrow for accurate inspection or minute enquiry. The water here and there is still dripping, and incrustations, usual in such grottos, coat the surface of the walls in some places. There are some whimsical likenesses, which the pen need not describe nor the pencil dehneate. Mr. Cookworthy, of Plymouth, a very ingenious man, and an excellent chemist, has been so obliging as to analyze the water of the three wells, and has found by many experiments, that it is very soft, and fit for every purpose. I therefore beg leave to congratulate your lordship on the discovery of this water, which, though there was no want before, cannot fail to be a valuable acquisition to your town of Stonehouse ; a place very delightful, and superior to most for the beauty of its prospects, and the elegance of its situation, and what is still better, for the goodness of the air, as the longevity of the inhabitants sufficiently evinces.
I have the honour to be, my Lord,
Your Lordship's most obedient,
and obliged humble servant,
FRANCIS GEACH.
