field notes 2017Posted by Vince Simmonds Fri, June 09, 2017 11:17:13BCRA 2017 Field Meeting:
Caves and Karst of the Gower Peninsula, Wales.
19-21 May 2017. A personal account.The Salt House, Port Eynon.
Walk: Pilton Green (NGR SS 4465 8710) via Long Hole Cliff, along the coast path back to the campsite at Port Eynon. The aim of this excursion was to look at various unrecorded resurgences, and a number of archaeologically sensitive sites.
John Cooper talked about the caves, karst and the glacial moraine that seals much of the limestone in this locality. Paviland Cave was not visited due to adverse tides, but the water levels didn't look much different to when I visited the cave a few years ago.
It was a pleasant stroll along the coast path, stopping every now and then to admire the view and discuss the geological out-crops.Oxwich Head Limestone Formation
, described as thickly bedded, fine to coarse-grained, recrystallized, bioturbated, skeletal packstones with distinctive pale to dark grey mottling and pseudo-brecciation and ooidal limestones. Units of dark grey, irregularly bedded skeletal packstones with shaly partings are developed at intercals. Thin unitof calcareous sandstone and sandy skeletal packstone [Pant Mawr Sandstone Member and Honeycombed Sandstone Member] at the base in Vale of Glamorgan and north-west crop of South Wales Coalfield respectively. Unit of ooidal limestone in lower part [Pendyrn Oolite Member] on north-west crop of South Wales Coalfield. Palaeo-karstic surfaces, overlain by red and grey clay palaeosols, punctuate the formation; thin coals developed in Gower (BGS iGeology online).
High Tor Limestone Formation
, mid-grey, predominately thick bedded, fine to coarse-grained, burrowed, skeletal packstones with thin beds and partings of shaly dolomite mudstone and siltstone. Some thin-bedded, dark grey bituminous packstones interbedded with thin argillaceous wackestones and mudstones. Coarse, locally cross-bedded, peloidal/skeletal/oolitic packstones/grainstones developed in lower and upper parts in north sections. On south-east crop of the South Wales Coalfield the formation is predominately dolomitized (BGS iGeology online).
A detour from the path was made to visit Long Hole
, a c.20m long, phreatic tunnel. The cave once had a thick sloping flowstone floor, but this had been excavated c.1850 by antiquarians, in the search for animal bones. Evidence for the flowstone floor visible, in places, on the cave walls. The animal remains recovered were from the last interglacial and the last glacial periods.
From here some of us continued along the coast path to Port Eynon, the rest returning to Pilton Green. On the way, those of us on the coastal path, stopped to admire Culver Hole
, it has been blocked with stonework construction to create a dovecote, or so one of the stories go.Saturday.
Today's itinerary involved two excursions, the first was to the Bishopston Valley, beginning at Barland Quarry. Meeting at the car park (NGR SS 5785 8968).
The geological sequence: Bishopston Mudstone Formation overlies Hunt's Bay Oolite Sub-group, which in turn overlies High Tor Limestone.Barland Quarry Cave
, was exposed during quarrying operations. A narrow rift section, c.40m long and c.10m high, ends at a small stream and choked sump. There are several remnants of caves (Kittle Hill Caves
) that are likely to be connected to the quarry cave. From here, we followed the Creten Stream to where it disappears into Bishopston Sinks No's 1 & 2
, there are a succession of, currently, dry sinks further down the valley.
Along the way we stopped to look at the fine Daw Pit
, it is an impressive sight.
Relic caves in the valley possibly indicate that the valley floor was c.10m higher. Ogof Ci Coch
was excavated by Rob Dinnis in 2012, no archaeology was encountered. A short detour was made to Gulver Pit
, another fine sight, described as a "large rent in the hillside". Guzzle Hole
is accessible for c.50m to the first sump. Beyond the sump, some 400m of passage have been surveyed by divers. Near the bottom of the valley the water can be seen to emerge from several springs.
The second excursion of the day was to Coed y Parc (NGR SS 5393 8975) to visit Green Cwm and LLethryd Cwm. These cwm's together form a c.1.5km dry valley in the centre of an extensive area of faulting.
In Green Cwm evidence for Upper Palaeolithic, Mesolithic, Neolithic, Bronze Age and Roman presence has been found in the caves and cliffs. There is a Neolithic chambered tomb of Cotswold/Severn type, known as the Giants Grave.
It is interesting that the re-constructive work at Parc le Breos has similarities to that seen at Stoney Littleton, Wellow in Somerset, another Cotswold/Severn type.
Although Cat Hole Cave
has a gated entrance the group were permitted access. In the cave, the roof consists of a number of high fissures, narrowing at the top. The base of these fissures has been eroded away to form the main chamber of the cave.Lower Cat Hole Cave.
Further up the valley, is found Llethryd Swallet, where I managed to gain access through the, now exposed, flood sink and re-emerge from the gated entrance.
On the way back down the valley a brief stop at Tooth Cave
, the longest recorded cave on the Gower Peninsula with over 1500m of surveyed passages. It is also an archaeologically sensitive site, hence the now gated entrance.Sunday.
Started the day on Cefn Bryn, where I parked the van, and walked over to visit Maen Ceti (Arthur's Stone), an impressive burial chamber.
The large boulder that forms the capstone, is an erratic carried to the hill top by an ice-sheet, it originates from Mynydd Carrig, located 40 miles to the north.
From the top of Cefn Bryn the topography of all of the area surrounding the next venue, Stout Hall can be seen. The underlying Old Red Sandstone rises on three sides to form a basin of limestone which was once filled with ice. At the southern the dip is south-east leading towards the Oxwoch Bay syncline, here the lower limestones are overlain with Marros Group Formations. Much of the area is covered by glacial diamicton, with the Paviland Moraine forming the south-west horizon.
Stout Hall Cave, has an impressive entrance, tall, c.1m wide, entering a lofty chamber. Daylight enters from other higher entrances.
The cave has been modified, there are several shot-holes to be seen. It has also been used regularly, in more recent times, as a dump. Bottles, broken pottery, rusty iron and ash forms a talus in one section.
There is evidence of recent flooding, wooden pallets wedged in narrow fissures, and leaves adhere to the main chamber walls to a height c.2m above floor level.Members of the group look at the results of a photogrammetry session in the cave.
The photography impeded the chance to explore fully but several geologically interesting features were noted, like this death assemblage.
It would be interesting to investigate the sedimentology in the main chamber, and some of the side passages, although the fill is fine, and rather sticky.
In the surrounding woodland there is plenty of scope for further cave development, albeit most likely to be choked.
Later in the morning, went over to investigate the site of a palaeo-lake in an adjoining field. Several potential 'sink' features were noted, and I'm not going to get into the argument about whether they are sinks or something else. In the field, medieval field boundaries were clearly visible, these are seen on a LiDAR image of the site distributed with the field notes for the weekend.
Walking back to the car park, I pointed out another feature, a drainage ditch parallel to a stone-built boundary wall has been channelled into a 'sink'. There were several mature trees growing over the stone wall, and it is possible that some working of the rock outcrop surrounding the 'sink' had occurred in the past. Close-by was a depression with some evidence of recent slumping.
That was the end of the action for the weekend. A thoroughly enjoyable field meeting, and a return to the area is planned.
field notes 2017Posted by Vince Simmonds Fri, June 09, 2017 07:00:058th June 2017:
with Jake, Nick and Tav.
After some recent torrential rain, it was a relief to find that there wasn't any water running into the dig.
We had a brief discussion about how best to proceed, as the dig gets ever deeper. The decision was that we should engineer the slope before continuing downwards. Jake and I began to dismantle the upper retaining wall and remove the sediment behind it. The rocks were stacked to one-side, as they will be required later. Tav and Nick were carrying out the hauling and spoil dispersal. With two people filling the skip, they were sometimes, rather on the heavy side, as Tav's back will attest. There will be several more sessions needed before forward and/or downward progress can resume. Also, the engineering works will help to protect the dig from too much slumping should it get wet and flood in the winter.
field notes 2017Posted by Vince Simmonds Fri, June 02, 2017 06:25:011st June 2017:
with Roz, Brockers, Nick, Tav and Duncan.
It was a fine evening, warm and sunny, there were grumbling's like "too nice to go underground". These were ignored and off we went.
At the dig, Brockers picked-up where he had left-off last week, the rest of us shifted and dispersed the spoil.
By the end of the session, some large boulders were beginning to appear, these will require 'capping' to reduce them to a manageable size and an interesting hole, to one-side was revealed. There is a lot of spoil to be moved before this can be fully investigated.
But now...it was time for the pub!
field notes 2017Posted by Vince Simmonds Fri, May 26, 2017 06:32:0525th May 2017:
with Roz, Brockers, Jake, Nick (and Duncan).
Duncan went to Edmonds Chamber to retrieve his rope, the rest of us went digging.
Inspired by Jake's attire last week, I too, went for a more minimalist approach, T shirt and over-shorts with a pair of Ron Hill's, still I was warm.
Brockers put in a sterling digging effort, aided by Nick, who was lowering the step-down as Brockers got ever deeper.
It was my job to load the buckets filled with sediment into the skip, Roz and Jake hauled the skip away and managed the spoil dispersal.
At the end of the session, the hole was deeper and boulders had been encountered, the finer sediment had, also become more granular. What does it mean? Keep digging and find out, I guess!
field notes 2017Posted by Vince Simmonds Fri, May 19, 2017 07:01:3318th May 2017:
with Jake, Tav, Jonathon, Dunc P, Matt and Mandy Voysey.
Me and Jake made our way to the dig, the rest of the team tarried awhile to admire the scenery. At the dig, Jake and I started to dig, it wasn't too long before we were joined by the others. Jonathon and Matt assisted Jake with the digging, Tav did the hauling aided by Mandy, Dunc and I were on spoil management. It was a very mellow digging session with plenty of banter. All too soon it was time for refreshment at the Hunter's Lodge Inn.
field notes 2017Posted by Vince Simmonds Mon, May 15, 2017 06:17:41
14th May 2017: with Brocker's. Also, Ray Deasy and Richard Abbot (MNRC).
Brocker's and me planned to dig the choke at the end of Sandy Tunnel, to which end
had bought along the capping gear. The other two went for a tour around and into Young Bloods in Wigmore.
We detoured on the way to the choke along the sixty-metre crawl, which is really more like 30m to assess the prospects there and, if necessary formulate a plan. An interesting looking space beyond has cool air emanating from it. The left-hand side is dominated by what appears to be a large, possibly detached flake, a few holes in the more competent right-hand side might be the best option. Anyway, that's a job for another day onto the choke.
Quickly, I got the capping gear into action and reduced a couple of large boulders as required, this enabled more digging. Removing smaller boulders, cobbles and some sticky mud, gaps could be seen at stream level.
Some shoring work might be needed, just to be on the safe side, scaffolding tubes would be a good option.
We were joined by the MNRC contingent briefly before they headed out of the cave. We carried on digging for a while longer before we, too made our way out. Good session.
field notes 2017Posted by Vince Simmonds Fri, May 12, 2017 06:29:07
11th May 2017: with Jake, Nick, Tav, Duncan, Roz, Roger Haskett, Dave King and Ray Deasy.
Roz took Roger up to chamber 20, Tav took Dave and Ray for a tour around, the rest of us headed up to the dig at the top of 20.
At the dig, Nick and Duncan rotated the digging effort, Jake and me hauled the spoil away. We were joined later by Tav and co., Ray and Dave went up to the end to assist with the digging, Tav helped out with spoil dispersal.
All too soon, it was time for the pub, it had been another enjoyable session.
field notes 2017Posted by Vince Simmonds Fri, May 05, 2017 06:06:094th May 2017:
with Jake, Tav and Duncan P.
The usual warm trip up through 20, even though we kept a relaxed pace. Ma and Jake took it in turns to dig, Tav and Duncan hauled and emptied the skip. The new digging buckets were put to good use and spoil was removed at a steady rate. The hole got deeper, it won't be too long before a ladder will be needed to get in and out.
There is some interesting layering within the sediments, evidence of successive flooding/drying events. Some of the laminations are compact, some less so.
field notes 2017Posted by Vince Simmonds Mon, April 17, 2017 09:24:5116th April 2017:
with Nick Hawkes, Paul Brock and Duncan Price.
This trip had a plan, to go and tickle the choke at the end of the sandy passage in Home Close Hole. I took the capping gear, just in case, but it was not required in the end, Brockers rigged the pitch and led the way, which was curious, as he has always expressed a dislike of pushing chokes.
We followed the inlet stream to where it issues from the boulder choke, then climbed the loose muddy slope to a point where further upward progress was not possible. A small gap was expanded and access to a small chamber was possible. It measured c.5m (l) x 2m (w) x 2m (h) was full of loose boulders and formed along a mineral vein, the floor wasn't too stable either. After a quick look around, Nick and Vince took it in turns to remove cobbles and boulders from an enticing looking space upwards. Nick managed to cause a slump of boulders that left things teetering on the brink. Nothing moved. We needed a rope, so all our belts were tied together and Vince got a loop over the chock-stone and pulled. That worked. A bit of gardening, Vince then accessed c. 7m (l) of horribly loose ascending passage that closed down to a very narrow fissure, there isn't a way on here. Here, many of the rocks have a black manganese coating, and there is a trickle of water.
Meanwhile, Duncan had spotted another gap leading downwards and needed assistance to open it up further. Eventually we abandoned this, made our way back down the slope, looked at some potential options off the slope, but after some discussion we decided the best plan was to dig at stream level where there is, at least one solid wall.
We went downstream a little way and climbed up another slope into the choke. Here, there is an open space beyond a precariously balanced boulder that would require moving if further progress was to be made. Gingerly, Vince used a small bar to ease the boulder out of the way, luckily, nothing more came with it. A short clamber up gained access to a gnarly, sharp, boulder passage, a couple of squeezes, it closed down after about 15m. There were some gaps overhead but, as a digging prospect it looked pretty hopeless. Duncan had noticed another space overhead, estimated c.3m (l) but this was not entered.
By now, it seemed everyone had had enough of playing 'ker-plunk' and Brockers was already on his way back to the pitch. Although Vince was last up the pitch, Duncan had waited and de-rigged. On the surface were Tony, Chris, Alice and Caroline, after changing, tea and sausage rolls was welcomed, followed by a de-brief about todays events. Then, we all headed off to a very busy Queen Vic for more refreshment.
field notes 2017Posted by Vince Simmonds Fri, April 14, 2017 08:21:31
13th April 2017: with Roz, Nick, Tav and Paul Brock.
Happy days! Back to digging and a good team assembled. The usual steady, warm trip up to the end of 20.
Tav and Brocker's took it in turns to dig, me and Nick did the hauling - a joint effort, while Roz emptied the skip and managed the spoil heap. Hauling was made considerably better with the replacement rope donated to the cause by Brockers.
No-one counted the number of bucket loads removed, but there was a good-sized hole at the end the session. The digger's reported that the sediment was becoming more compact and it's not easy to work-out just where the water has gone.
As ever, we'll just keep digging on.
field notes 2017Posted by Vince Simmonds Wed, April 12, 2017 05:55:0211th April 2017:
The main purpose of the trip was to have another look at the water level in the dig, so that we can get work there underway. It was noticeably drier on the approach through the cave passage.
At the top of 20 we paused to investigate a curious gurgling sound being created by a trickle of water through a tiny fissure in the rock. We, then collected the digging kit we had stashed about a month ago and took it down to the dig, some of it will be useful I'm sure. The small side passage, that overflows into the dig was dry. I was optimistic that the dig would be dry. It was!
After sorting-out the digging kit, Nick suggested that we remove the clay film that had settled as the water had receded. So, that we did, taking turns to fill the bucket with the claggy sediment and load the skip. Hauling the skip wasn't so easy either, the haul rope could do with replacing, then there was the thixotropic slop to be removed from the skip. But, we managed to get most of the slumped and settled material out and the digging should be easier next session. Hopefully, more of the team will be available and that will make the task a whole lot better.
Time for refreshment, another warm, thirst inducing digging session.
field notes 2017Posted by Vince Simmonds Sun, March 26, 2017 14:05:32
Herb Paris unfurling in Harptree Combe. This plant species is an indicator of ancient woodland.