The Mellte Valley Part 5 - Description Of Sites West Of The River


In the following descriptions the grid references have all been checked by site investigation. In many instances the descriptions themselves are based on personal exploration. However, in those cases where it has not been possible to make a personal visit the descriptions have been taken from the literature. The length and vertical range of all caves is quoted where it is known.

To help in the assessment of the speleological significance of the sites they have been classified as:

Sinks (S)
Risings (F)
Unconformity Caves (U)
Others (O)

The site reference numbers at the head of each description relate to the numbering used on the general area map of the Mellte Valley.

The literature reference numbers at the bottom of descriptions relate to bibliography which will form part 6 of this study.

The inclusion of any site in this listing does not imply that a right of access to it exists. Indeed, in some instances it almost certainly does not and such access, if sought, would almost certainly be denied.

The Sites

37) Ogof Carnau Gwynion (O) Alt. Name Ogof Carnau Gwynion Caves

N.G.R. SN 9173 1486
L=10m VR=?

Small cave in the crag of Carnau Gwynion with two entrances.

References: 1, 12, 14, 25 (inc. survey)

38) Theoretical Pot (O) Alt. Name Gwynion Gulf

N.G.R. SN 9162 1476
L=8m VR=14m

A development of the bottom of a shakehole high on the Shar Wlad consisting of a shaft with a narrow entrance

References: 1, 12, 14, 25 (inc. survey)

39) Ogofau Gvynion (O)

N.G.R. No1 SN 9211 1462 No2 SN 9210 1461
L = l00m (total) VR = ?

These two small caves lie in the face of a small quarry behind a disused limekiln at the summit of Carnau Gwynion. They are both typical phreatic caves and almost certainly form remnants of the same truncated system. They consist primarily of constricted tubes formed in the bedding, which dips 10 to the South. Three chambers have been formed in No.1 by breakdown along joint lines.

From their location at the high point on the moor it is evident that they must be of great age, having been formed before the downcutting of the surrounding landsurface, and probably before the removal of the overlying strata. Deposits of red silty clay, which choke the passages, are probably derived from the Old Red Sandstone and are, in places, covered with calcite deposits. these are inactive and must date from a much earlier phase in the development of the cave. No water enters the caves today, except for a large amount of drip water from the roof during wet weather.

To the North of the cave entrances there is a closed depression which drains the North side of Carnau Gwynion, but this does not contain any open caves.

References 1, 12, 14, 17 (inc. survey), 25 (inc. survey)

40) Sink (S)

N.G.R. SN 9200 1438

A boulder filled fissure in the dry valley running South from Ogofau Gwynion. It lies directly in the middle of the trackway and takes water during heavy rain.

Reference 17

41) Sink (S)

N.G.R. SN 9197 1431

Another boulder filled fissure slightly lower down the valley from 40. This also takes quite large amounts of water during rain without backing up.

Reference 17

42) EINON'S HOLE (O) Alt. Name Innion's Shaft

N.G.R. SN 9196 1424
L = 0m VR = 8m

Small cave leading down from the bottom of a small shakehole. Entrance blocked with brushwood.

References 1, 12, 14, 25 (inc. survey), 34

43) Y GWAL (O)

N.G.R. SN 9205 1391
L = 30m YR 10m

An open pothole in the surface of the moor which is surrounded by a dilapidated fence. The entrance is formed by the collapse of the passage below. It can be descended via a muddy slope using a handline. This leads to a single keyhole shaped passage of impressive size which stops abruptly at a mud choke. A dig at low level has entered a length of bedding cave taking a small stream.

The cave represents an ancient deserted stream passage. Since it is not associated with any surface valleys it is possible that it is part of an ancient system formed prior to the shaping of the moor as it today.

Nearby a line of shakeholes marks the course of a fault across the moor.

References 1, 11, 12, 14, 24, 25

44) HOLE BY THE WALL (O,S) Alt. Name Mutton pot; Hole in the Wall

N.G.R. SN 9209 1351
L = 50m YR = 4m

This is an open pot at the bottom of the lowest of a whole series of shakeholes which pepper a large closed depression on this part of the Shar Wlad. The wall referred to in the name is in a state of complete collapse and runs close by.

The cave descends through boulders to the head of a very narrow rift which can be followed for some distance before it becomes blocked by boulders. Attempts at blasting have not, as yet, yielded success. In addition, Williams (ref.28) reports a long bedding plane extension to this cave. The pot takes very large amounts of water during rain and must be connected with an important drainage system below the moor. The water entering here has reportedly been traced to Porth Yr-Ogof Rising (q.v.).

This site does not lie directly on the nearby fault the line of which is marked by a straight line of shakeholes further North towards and West of Y GWAL.

References 1, 11, 12, 14, 25, 27, 28, 35


N.G.R. SN 9225 1346
L 3m VR = Om

As the name suggests the entrance to this cave is very obvious, situated as it is high on a crag overlooking the shakehole pitted depression which contains Hole by the Wall. It is a typical U-type feature in a cliff which has been created by the downcutting of the adjacent valley and enlarged by frost action. It consists of a large rockshelter 2m high, 3m wide and 3m long which is much used by sheep as a shelter. There are several other small cavities in the unconformity nearby. A section DI' the limestone/gritstone interface is particularly well displayed at the back of the cave.

A broken millwheel near the cave indicates that the site has been quarried and this may have been instrumental in the enlargement of the cave.

References 1, 12, 14


N.G.R. SN 9118 1341

A very large wooded depression drains water from the surrounding bog. The water sinks at the base of a limestone cliff but past digging attempts are now silted up. The destination of the water is unknown.
The sink forms a small blind valley at the head of a larger valley which runs down to Pwll-y-Gelynen.

References 1, 12, 25

47) RHODODENDRON HOLE (U) Alt. Name Rhododendron Pot

N.G.R. SN 9237 1289
L = 6m YR = 3m

This open pothole lies in a small area of peat covered gritstone which provides a thin cap for the limestone at this point. The entrance is completely dominated by a rhododendron bush below which a 3m deep pit can be found about 6m long and 3m wide. A small chamber formed in the uncomforniity can be entered at the Northern end.

References 1, 12, 14, 25 (inc. survey)


N.G.R. No 1 SN 9239 1281 No 2 SN 9240 1280
No1 L = 10m VR = 3m
No2 L = 10m VR = 2m

These are two short open rifts in an area of heather moor. The two holes are both evidently formed in the same major joint or fault as the nearby Rhododendron Hole. The two caves consist of narrow openings in gritstone about in wide; both contain large amounts of rubbish. No 1 is the most Southerly and descends about 3m to a short development about 10m along the Joint at the level of the P/A unconformity. No 2 is a few meters to the North and of similar character.

References 1, 12, 14, 25 (inc. survey)

49) PWLL-Y-GELYNEN (S) Alt. name Pwll-y-Gelynen Sink

N.G.R. SN 9185 1282

A large wooded depression takes water from at least two directions which sinks in a small poe1 at the bottom. The sink forms the end of a blind valley which precedes the head of the Nant-y-Carad stream in a boggy plateaux to the South.

The sink lies directly on the fault which has brought the gritstone into contact with the limestone at this point. Although the destination of the water is unknown, it seems likely that it will follow the line of the fault towards the I(ellte. The rising site No36 (q.v.) lies on this fault.

References 1, 12, 14

50) PLAS-Y-DARREN POT (U) Alt. names Plas-y-Darren N (orth); Plas-y-Darren Cave

N.G.R. SN 9227 1262

This is an unconformity cave near Plas-y-Darren farm. It is surrounded by a barbed wire fence.

Reference 12, 14, 35

51) OGOFAU PLAS-Y-DARREN (U) Alt. Names Ogof Plas-y-Darren; Ogof-y-Darren; Plas-y-Darren Fissure; Plas-y-Darren Potholes (Nos 1 & 2)

N.G.R. SN 9203 1239

This is a complex unconformity feature near Paut-y-Llwyn farm. A cave is formed in the P-D unconformity (Ogof Plas-y-Darren) beneath a prominent shelf of gritstone over which a small stream flows to sink in boulder choked shafts in the limestone below (Plas-y-Darren Potholes).

References 12, 14

52) PANT-Y-LLWYN CAVE (U) Alt. Name Pant-y-Llwyn Fissures

N.G.R. SN 9216 1238

An obvious cave on the gritstone scarp behind Pant-y-Llwyn farm. this is a typical U-type feature.

References 12, 14

53) PANT-Y-LlWYN RISING (R) Alt. Name Pant-y-Llwyn Farm Resurgence; Pant-y-Llwyn Rising West

N.G.R SN 9215 1228

A fairly strong spring rises from impenetrable bedding in the limestone just south of Pant-y-Llwyn farm. The spring is used as a water supply for the farm.

The source of the water is unknown but is probably collected percolation water.

Reference 12, 14


N.G.R SN 9268 1230

This spring flows only during wet periods.

Reference 12

55) SPRING (R)

N.G.R. SN 9280 1310

A spring at river level in the West Bank of the Avon Mellte.

56) SPRING (R)

N.G.R. SN 9288 1344

There is a spring adjacent to the track leading up to the Shar Wlad from the village. It has a cistern built around it and used to provide a water supply to the village tap ( now disused). Two other similar springs exist further South in the same field. All rise from the boulder clay.


N.G.R. SN 9275 1370

This is a strong spring which flows for most of the year from the limestone at the boulder clay boundary at a fairly high elevation on the Vest side of the valley.


N.G.R. SN 9213 1356

A massive collapse in the base of an existing shakehole in 1982 has created a large conical depression with very loose sides. It is about 10m deep. At the bottom what appears to be solid bedrock can be seen. The site is now surrounded by a barbed wire fence.

Reference 34


N.G.R. SN 9165 1440
L=60m VR=8m

A small cave can be entered from a narrow rift in a limestone crag high on the Shar Wlad . It was discovered in 1981 and subsequently dug by CCC. The entrance gives access to a small branching passage. All ways on are too tight.

Reference 36

60) SINKS (S)

N.G.R. SN 9257 1500

There is a group of wet weather sinks at this position on the Northern limit of the limestone outcrop.

Reference 35


N.G.R. SN 9286 1413

A spring rises from the boulder clay near Nant-y-Croen farm.

62) CAVE (U)

N.G.R. SN 9246 1225

A small cave formed under the gritstone near to Nant-y-Carred farm. The entrance in the gritstone scarp leads to a chamber containing rubbish and putrefying sheep corpses. A small passage leads to a climb down and a choke.

Allan Ockenden