The Mellte Valley Part 3 - Description Of Sites East 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 a 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 spelaeological significance of the sites they have been classified as:

Sinks (S)
Risings (R)
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 Mehlte Valley on page 16.

The literature reference numbers at the bottom of descriptions relate to the 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

1) OGOF GWAEN CEFN-Y-GARREG (U) Alt. Name Gwaen Cefn-y-Garreg Rock Shelter

N.G.R. SN 9421 1340
L=5m VR=?

A large rock shelter formed entirely on gritstone in the side of a collapse dohine near the summit of Gwaen Cefn-y-Gareg. The cave has formed by the collapse of the surface of the moor into a cavity in the limestone some 10m lower down. Thomas (23) imputes some very larg dimension to the initiating cavity that must have produced this and other similar collapse dolines on the moor.

The Site is identified by a Rowan tree growing in the entrance.

References: 12, 14, 15 (inc. survey), 18

2) Rock shelters (U)

N.G.R. SN 9415 1342

A series of rock shelters formed in the Post-Dinantian unconformity in this area where it is expossed in a cliff.

The specific site refered to by Lloyd (18) at SN 9414 1338 is difficult to identify.

References: 15, 18

3) Cave (U)

N.G.R. SN 9406 1302

An unconformity feature leading down below a crag.

References: 12

4) Sink (U) Alt. Name Gwaen Cefn-y-Garreg Sink

N.G.R. SN 9408 1297

An unconformity doline with a Rowan tree just above the wall taking a small amount of water with no cave accessible.

References: 12, 14

5) Cave (U) Alt. Name Lesser Pulpit Hole

N.G.R. SN 9407 1290
L = ? VR = 19m

Typical unconformity doline just below a wall with a cave leading down. The new cave refered to by Bull (21) and Lesser Pulpit Hole refered to by Stratford (14) probably refer to this site.

References: 12, 14, 18, 21

6) PULPIT HOLE (U) Alt. Name Gwaen Cefn-y-Garreg Pot, Buttertubs Cave

N.G.R. 511 9406 1281
L = l00m VR = 15m

This is the most important of the U-type caves along the Post-Dinantiau unconformity on the western edge of Gwaen Cefn-y-Gareg. It is reached by a stile over the forest fence from the Sennybridge - Penderyn Road. The entrance is a wide cavern with a prominant rock standing up at its centre - the Pulpit. The cave is developed in the bedding with several routes leading down into pits in the floor mainly to the east and south. The earlier passage is noted for its red liquid mud.

The Buttertubs refered to by Stratford (14) at 941 128 probably refers to this cave.

References: 9, 11, 12, 14, 15, 18 (inc. survey)

7) Cave (U)

N.G.R. SN 9410 1275
L=25m VR = ?

Small unconformity cave just above the boundary wall.

References: 12, 18


N.G.R. SN 9412 1255
L=5m VR=?

A large cavern formed in the P-D unconformity just below the forest boundary fence which takes a small of water. Light penetrates to all corners of the cave!

References: 12, 14, 18

9) Dig (U)

N.G.R. SN 9411 1247
L=60m VR=?

A timbered shaft at the north east corner of a large doline north of Pwll Derw; It is difficult to find because of the forestry. The shaft has now run in at the bottom but it is reported to have lead to about 60m of passage.

References: 18

10) Doline (U)

N.G.R. SN 9412 1240

A collapsed doline in the gritstone a few metres north of Pwll Derw which is difficult to find amongst the trees. A small cave leads down from the west side.

11) PWLL DERW (S) (U) Alt. Name Pwll Derwen (in error)

N.G.R. SN 9413 1235

An impressive sink in the forestry land just to the north of the Mellte Castle - Penderyn Road reached by a style over the forestry fence. A fairly large perenial stream runs off the gritstone moors into a huge steep-sided doline and sinks amongst massive gritstone boulders on its western side. The site has been dug by CCC and others without success. A small cavity exists high up on the north side of the doline above the sink.

The sink has evidently formed in a collapsed doline caused by solution of the limestone beneath the gritstone cap rock. Although the gritstone is about 15m thick here~ the bottom of the depression must be a few meters above the limestone interface. The fact that water drains freely (except in exceptional conditions) into this sink indicates that sizable fissures must exist in the limestone. The water has been traced to the Hepste Valley.


N.G.R. SN 9375 1420

A strong spring in wet weather is situated just below the road north of Garreg Fawr Farm. The source of the water is unknown.

13) FFYNNON GARREG FAWR (R) Alt. Name Rovers Cave, Ogof Garreg Fawr

N.G.R. SN 9379 1387
L=500m VR=?

An extensive cave which runs into the hill from the strong spring below Garreg Fawr Farm. It consists mainly of constricted, waterlogged bedding planes. The entrance was opened in 1969 using explosives. A tight squeeze leads to a series of sumps which can be bypassed until a terminal sump is reached about 500m from the entrance. A tributary joins the main stream near the end of the cave. Until recently the previous farmer did not allow cavers to visit the cave and it probably remains only partly explored. The source of the water is not known and there is no clearly identifiable sink that can be associated with the resurgence. It seems likely that the water is mainly percolation collected from a wide area.

References: 2, 7, 11, 14, 18

14) Sink (S)

N.G.R. SN 9337 1278

Water overflowing from Llyn Bach sinks into a series of mud floored shakeholes. There are numerous other shakeholes in the small limestone plateaux below the crags of Gwaen Cef-y-Gareg, several of which take small streams.


N.G.R. SN 9324 1224
L = 150m VR = 20m

This cave is entered from the most northerly of the line of shakeholes along a fault above Cwm Porth Farm and is marked by a dead hawthorn tree. It consists of a typical unconformity development along a fault with sharp rock flakes and numerous blind shafts in the floor. The line of the cave trends in a northerly direction with the shafts progressively getting deeper.

References: 9, 11, 12, 14, 18 (inc. survey)


N.G.R. SN 9326 1221
L = 6m VR = ?

A short cave in the Post-Dinantian unconformity with no vertical development. The cave is situated in one of a line of large shakeholes on the moor above Cwm Porth Far. It takes water during heavy rain.

References: 9, 11, 12, 18 (inc. survey)

17) OGOF FFYNNON (U) (O) Alt. Name Ogof Ffynnon Fach

N.G.R. SN 9341 1202
L = 1000m VR = 30m

The most southerly of a line of typical unconformity caves entered from large shakeholes on a weakness in the gritstone (caused by a fault line) above Cwm Porth Farm. The cave has an impressive entrance on the west side of the shakehole which leads directly to a collapse chamber formed under the grit. The floor is a rubble of limestone an grit boulders and the limestone and shale walls are deeply fluted by dripping percolation water. At the north end of the chamber a route down through the boulders leads to a north-south rift with two ways on.

The south route leads, via a flat out crawl, to another long boulder chamber with a few straws. A narrow drop at the far end of this chamber leads down amongst the unstable boulders until an exit is wade from the base of the choke into a clean washed passage in white limestone. All ways off this are choked; a sump may be reached upstream which is only known to drain after prolonged hard frost. When open, this sump leads to an extension that can be followed for about 500m. A succession of muddy and constricted crawls and chambers lead to a 6w pitch below which the passage soon chokes. Much of this passage appears to be fault-guided aligned along the 330-150 degrees axis of the fault on which the entrance lies. A major shale band appears to be the primary statigraphic control.

Following the rift north a crawl leads to a large chamber floored with very big boulders. An old iron Ladder may be climbed 5m to gain access to the continuation of the fault at roof level. This leads to several small chamber, until a dig is encountered at the end.

Water sinking at the entrance disappears into the underlying boulders and reappears 100m lower down in Cwm Porth Inlet in Porth-yr-Ogof. The sump resurges a large quantity of water in wet weather which joins the water sinking at the entrance and disappears into the boulder choke ramp that leads down to the stream passage from the entrance. It is clear that the whole length of the extension sumps under such conditions, although the source of this water and its point of ingress into Ogof Ffynnon

References: 9, 10, (inc. survey), 11, 12, 14, 18 (inc. survey), 29 (inc. survey), 37

18) Sink (S)

N.G.R. SN 9359 1218

A small stream sink in a collapse doline in the gritstone adjacent to the old tramway.

References: 14

19) PWLL-Y-PHAIADR (S) (U) Alt. Name Pwll Coed-y-Phaiad, Pool Swallet

N.G.R. SN 9364 1190

A large collapse feature surrounded by dense forestry which takes a stream from the South East and another stream from the North. The depression is hour-glass shaped, the southern part containing a permanent lake which overflows to sink in the slightly lower northern part. The origin of the sink is likely to be the similar to 11 - Pwll Derw. The destination of the water is similarly likely to be the Hepste Valley.

References: 12, 18

20) CWM PORTH CAVE (U) Alt. Name Ogof Sulgwyn

N.G.R. SN 9198 1213

This cave is located at the head of the small valley running down to Cwm Forth Farm. A small stream runs off the afforested land and over a gritstone cliff to sink at this site.

Burke (9) lists this cave as A-G. Jenkins and Williams (11) describe a large cave at this grid reference but the description appears to be one of Cwm Porth Caverns, probably A-G. Baguely (12) mentions an Ogof Sulgwyn near to this site. It seems that the two are in fact one, Baguely having an incorrect grid ref. (See correction below)

References: 9, 11, 12, 18


N.G.R. SN 9194 1221

This spring is used for water supply to the farm just down the dry valley from Cwm Porth Cave and is probably the resurgence of the water from this site.

References: 12, 14, 18

22) CWM PORTH CAVERNS (U) Alt. Name Cwm Forth Woods Caves, Cwm-y-Porth Wods Caves

L up to 70m VR = ?

Cwm Porth Caverns constitute a classic series of caves formed under the gritstone caprock. At least 35 entrances are identified in the literature as existing along the gritstone/limestone boundary in the woods to the south east of Cwm Porth Farm. None are easy to find in this dense forest and some (those located furthest from the gritstone/limestone boundary) virtually impossible to get at now. The caves are of a classic unconformity type and are characterised by collapse features with overhanging gritstone cliffs on the east side and a jumble of boulders in the base. These collapse dolines form the entrances to the caves. In most cases the cavities associated with them are fairly insignificant, however some of them interconnect thus forming large size passages up to 200ft long. Drip water collecting in the caves seeps away through boulders and blind shafts in the floors and has been shown to resurge in the series of springs located below sites 25 and 26(q.v.).

The caves that can still be located form six distinct groups. All of these caves were studied in some detail by Burke (9) and his identification letters have been related to the six groups.

(a) SN 9281 1191 A-F A large collapse feature several entrances under a long gritstone cliff.
(b) SN 9287 1188 H-J A series of cavities located along the gritstone boundary. Some interconnect underground.
(c) SN 9287 1185 K-L Two interconnected entrances at one end of a large doline.
(d) SN 9288 1182 H-N A sizable stream sinks here after falling over the cliff on the east side.
(e) SN 9288 1178 0-R An interconnected series of chambers running south from a large doline.
(f) SN 9288 1176 T-V Another interlinked series of cavities.

The sites Burke identified as W-AF, which should lie further to the N.E., are those which are now difficult to locate. A-G would appear to be the same as Cwm Forth Cave (site - 20).

References: 9 (inc. survey), 12, 14, 18

23) Sink (U)

N.G.R. SN 9280 1157

A large collapse doline on the P-D unconformity which takes a small amount of water from the hillside.

References: 18

24) Spring (R)

N.G.R. SN 9276 1150

An intermitent spring from unstable ground located just above the wall near a derelict barn. This is probably the most southerly of the line of U-type features along the gritstone boundary.

References: 18

25) Rising (R)

N.G.R. SN 9277 1182

A stream emerges from boulders and flows west to join the Mellte. The water comes from Cwm Porth Caverns.

References: 18

26) Rising (R)

N.G.R. SN 9275 1165

A stream emerges from boulders and flows west. To the Mellte near Ogof Glan Mellte. The water derives from Cwm Forth Wood Caverns.

References: 18

Frank Baguley, Hon. Secretary of the Cambrian Caving Council writes in the Council's Newsletter No.6, 1988-89 to correct a mistake in the above article which appeared in Pelobates 53. He states:

Re. entry 20, that Ogof Sulgwyn and Cwm Porth Cave are the same, and that I did not give the correct Grid Reference. I would point out that Cwm Porth Cave was an open cave which existed before Ogof Sulgwyn was opened up by myself digging in a semi-circular shakehole. Peter Bird, Tony Burke, my son and myself worked on it in Whitsun 1963 - hence the name Ogof Sulgwyn. It does not take a stream of f the moor and has no gritstone cliff.

Whilst we take pains to be as accurate as we can in Pelobates we do sometimes slip up and are grateful if readers point out to us our errors.

Allan Ockenden