OUCC Proceedings 4 (1966)
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The O.U. Cave Club has been active in South Wales in 1965.
A fortnight of terrible weather endured by the authors in March, 1965, produced concrete results in the shape of the extension of this little-known cave in Pant Sychbant.
The cave is situated at N.G.R. SN 9707.0972, at a height of c. 975' OD. The entrance lies in the westerly of two adjacent sinkholes, the easterly taking a fairly large stream. The cave shows signs of having been entered initially by digging, and the farmer upon whose land the cave is situated, Mr. G. Davies, tells us that he remembers some local boys being active in the area in the early fifties. This story is confirmed by Mr. Melvyn Davies of the B. N. S. Who says that the cave was probably first entered by the boys of Monmouth School led by Cullingford. He says also that Gordon Clissold dug in the cave in 1955.
When we first entered, a short entrance shaft led to a small chamber with a boulder floor, from which a squeeze to the left gave access to a 10' shaft. At the bottom of this a stream was met, which could be followed until it sank in boulders immediately under the entrance chamber. Traversing across the head of this shaft, a slide down to the right led to another chamber with a long, downward-sloping tube in the floor at the bottom of which could be heard faintly the noise of falling water. A half-hearted attempt to dig at the bottom of this tube was abandoned when it produced no quick result and we turned our attention to the entrance chamber. The whole entrance series is rather unstable.
By shifting some large boulders in the floor of the entrance chamber, access was gained via a very disconcerting squeeze to the head of a smooth, water-worn shaft down which we could just slip without dislodging several tons of unstable boulders jammed in it. The shaft opened out into a short rift, blocked at the end, which is, at the present moment, full of stones removed from the floor. Digging in the floor, we got into a downward-sloping bedding plane, also choked with stones. This was cleared and the debris deposited in the rift above.
At the bottom of the bedding plane was a jumble of large, unstable boulders, and it was at this point that we would have given up had it not been for the extremely loud rumble of water that we could hear through them after heavy rain. The bedding plane was named Twll y Mochyn after the unique character of the mud found there.
After very many false attempts, we broke through the boulders into a stream passage. As is the wont of those breaking into new caves we told ourselves that this was IT, another Agen Allwedd! Alas for us, after a few right-angled bends, the stream sank into the floor, as did the roof. The next day, after some impotent scrabbling, we at last broke through this obstacle too, into a largish, low chamber. The floor of this chamber is of large boulders, and one has only to climb down through them to stream level to see what a nasty specimen of a choke it is. This is definitely the end of the cave for the moment. Just recently we have been digging in a bedding plane off the main chamber ( not shown on the survey ) which appears to continue indefinitely.
Worthy of mention also is a small but attractive inlet passage leading up off the main chamber which provides a sporting ten minutes.
One of the distinctive features of the cave is that the greater part of it is developed along a single shale band, the passage above this shows a high degree of joint control. Development along the shale band has also given rise to an extensive network of oxbows off the main stream passage. Several of these oxbows contain a stratified fill possibly of glacial origin. Quantities of eroded stalagmite in the upper reaches of the cave and large quantities of alluvium, in view of the nature of the stream now entering the cave, probably originate from an earlier period of the cave's history, deposited before the present, active development had begun. The whole system now totals some 800' in length and the extension is shown in the accompanying survey.
Our thanks are extended to Mr. And Mrs. G. Davies of Wern Las, Cadlan, whose kindness and hospitality have made the exploration possible, and to Paul Deakin of the Eldon Pothole Club who drew the survey.
F. E. Sanders
R. J. Cooper
Several visits to this most impressive of sinks have been made. Unfortunately, on all occasions, inclement weather and/or dead sheep have not allowed a very close look to be taken. Since I wrote the above I have learned that the B. N. S. have re-opened an old dig and are making good progress, although this has been slow as they have encountered archaeological material. Thermal currents in the dig apparently indicate a cave rather than a 'pot'. Still, all that water must go somewhere and the prospects for a large cave system are good.
The following is a summary of findings and conclusions after an afternoon spent examining shakeholes on the southern edge of the grit capping of Gwaen Cefn y Garreg.
N.G.R. SN 9477.1172 at c. 1025' OD. A stream sink 100 yds. N of Tir Duweunydd farm, two sinkholes connected by a rock arch. These might repay attention but to dig them out would be an extensive operation.
N.G.R. SN 9478.1180 at c. 1050' OD. A small shakehole with a visible opening 100 yds. E of the above. The entrance leads down into a small chamber with interesting mud formations on the roof. The roof is gritstone while the chamber is developed in the underlaying limestone, the division being clearly marked. The two rocks are quite conformable. Off to the right of this chamber, a hole that was not seen until the last minute led, after a little enlargement, to the head of a very unsafe 25' pitch. Huge boulders all around appeared to be held in by nothing but mud. The landing at the bottom of the pitch is onto a heap of black gritstone boulders. There is a small aven to one side and a very short descending passage, both choked with debris. The pitch is remarkable for some rather fine fluting and for the occurrence, at regular intervals of a few feet, of perfectly horizontal bands of chert at an advanced stage of desilification.
N.G.R. SN 9480. 1195 at c. 1050' OD. East of the above and an active stream sink. It is a shakehole, half filled with rubbish, where there has been a recent collapse of the face, but despite this, an opening can be seen under the debris and might repay further attention.
N.G.R. SN 9494.1207 at c. 1100' OD. On the other side of the mountain road to the above, near the gate. It is a larger shakehole than the others with a visible opening leading to boulder-floored chamber once again developed immediately under the basal grit. Through holes in the rather unstable floor can be seen two openings, while a squeeze on the right leads to the head of an obviously unsafe pitch of about 25' depth. This was not thought worth the risk involved in descent.
Despite the repeated efforts of several clubs, notably B.N.S.S.S. only a small portion of the long underground course of the Hepste has been traversed. Inlet passages from sinks in the valley sides may provide a way in, although all sinks investigated to date have been hopelessly choked.
It is hoped that after a little more work it will be possible to publish a rather more rigid geomorphological account of some of the particular features of the Hepste and Cwm Cadlan-Pant Sychant valleys.
F. E. Sanders