Siambre Ddu trip 07/10/2023
Unless otherwise stated, camera, setups, lighting, edits and gallery effects by Tarquin. Modelling and lighting at various points will be Steph Andrews.
The name of this cave uses an archaic spelling, and should be Siambr Ddu. However, it is almost always written Siambre Ddu, sometimes mistakenly Siambra Ddu, and for some reason Siambri Ddu in the cave registry. It was recorded in 1967, which is apparently so long ago that the archaic spelling is now preserved in spite of it not being the normal modern spelling (much like how waterfalls in South Wales get written as Scwd, Scŵd or Sgŵd instead of Sgwd).
However you spell it, it is a very unusual cave. It should not really exist. It is not a natural limestone cave, and is really just a shakehole that failed to reach the surface. The cave formed when Siambre Ddu Passage in Ogof Draenen collapsed. The collapse propagated upwards from the Gilwern Oolite, through the limestone shales of the Llanelly Formation, and into the relatively weak Twrch Sandstone Formation (formerly Millstone Grit, a much better name). Normally the Twrch Sandstone Formation is not strong enough to support such an enormous chamber, and the collapse would be expected to continue upwards, creating a shakehole. However, here it survived, in spite of one edge clipping the surface enough to open an entrance. Not being limestone, the rock contains very unusual fossils for a cave, particularly a large number of trees, with incredible details preserved. The walls and ceiling are deeply stained black by manganese from the peat bog, which gives the cave its name, meaning "black chamber" or "black cavern".
The remains of the Blackwalls caving hut, which was used by Oxford University Caving Club during the exploration of Ogof Draenen.
Modelling by Steph
Looking towards Cwm Llanwenarth from the open land below the former Lamb and Fox pub. Lamb and Fox Chamber in Ogof Draenen sits underneath the field in front of the camera, and Megadrive North and Underworld Series are beneath the right edge of the field. The pub itself sits over the junction of White Arch Passage and Back Passage, close to Tea Junction. In the background are Gilwern Hill (441 metres, the part containing Waterfall Series), Pen y Gadair Fawr (800 metres), Pen Twyn Mawr (658 metres), Pen Gwyllt Meirch (580 metres), Disgwylfa (540 metres), Crug Mawr (550 metres), Sugar Loaf (596 metres), The Skirrid (486 metres), Edmund's Tump (423 metres) and the Blorenge (561 metres, but not the part containing Ogof Draenen).
Former sidings on the Hill's Tramroad. These sit over Anastomosis Passage, Faded Love and Blue Eyes Cryin' in Underworth Series, with Megadrive North ending just beyond them. The Lamb and Fox pub and Pwll Du Adventure Centre can be seen on the left, with the rope climb in the Entrance Series below the adventure centre, and the entrance below the grassy slopes to its right. Waterfall Series ends below the radio mast on Gilwern Hill ahead. Pen Cerrig-calch (701 metres), Table Mountain (451 metres) and Waun Fach (811 metres) are now visible between Gilwern Hill and Pen y Gadair Fawr.
Cutting on the Hill's Tramroad. The camera is over the top of the end of Siambre Ddu Passage, with Siambre Ddu itself being at the far end of the cutting.
Fossil tree imprint in a lump of quartz conglomerate in the cutting.
Pwll Du Quarry, with Hill's Tramroad running along the ledge near the top. Siambre Ddu Passage runs parallel to the quarry, about 30 metres behind it, and the Nunnery is about 60 metres behind the camera. Siambre Ddu itself is in the mouth of the tramroad cutting at the top of the quarry. The stone lined shaft on the left is the top of the balance shaft, which was powered by the stream on the left. The entrance to Balance Shaft Cave is in the gully at the bottom of the quarry below it. The sink that supplies the Black Beetle streamway is in the middle of the quarry, but is currently dry.
Hill's Tramroad has fallen into the quarry, and the path along it is now a very narrow ledge. The tramroad is fenced off on one side and walled off on the other.
Modelling by Steph
The Twrch Sandstone Formation is very visible at the top of the quarry. Two bands have very visible large quartz pebbles.
The top of the balance shaft, which funnels in before you can see the bottom. An empty tram truck would be put onto one of the two carriages that ran up and down the balance shaft, at the top. A truck loaded with limestone would be put into the other carriage at the bottom. Stream water would be directed into the bottom of the empty truck's carriage, until it was heavier than the loaded truck in the other carriage. It would then sink down the shaft, pulling up the full truck with a cable that ran over a pulley at the top. The full truck would be removed from its carriage at the top, the water would be emptied from the carriage at the bottom of the shaft, the empty truck at the bottom would be removed from its carriage and replaced with a full one, an empty truck would be put onto the carriage at the top. The cycle would be repeated, lifting limestone using water power.
Modelling by Steph
The entrance to Balance Shaft Cave at the bottom of the quarry.
Balance Shaft Cave starts very low, filled with sheep and fox scat. At most, it is stooping height. However, it would once have been large enough to fit tram trucks through, before it got filled in with quarry debris.
Modelling by Steph, lighting by Tarquin, Steph and Sol
Metellina merianae cave spider, which appears to be female.
Modelling by Arianwen
Shotholes in the walls show that the quarry workers had enlarged parts of the passage to allow the tram trucks to fit.
Modelling by some grains of sand
Fossil shark dorsal spine, probably a Ctenacanthus.
The only side passage is very short and narrow, but is shown much larger than it is on older surveys. The only other alcoves are full of animal bones.
Crawl from the larger passage into the bottom of the balance shaft. It would have been a good idea to wear proper caving gear here.
Modelling by Steph, lighting by Tarquin, Steph and Sol
Looking up the balance shaft. This is about 20 metres tall.
Lighting by Sol
Black beetle, a devil's coach horse beetle, on the wall of the shaft.
Modelling by a shining shiny dæmon, lighting by Tarquin and Sol
Stal in the balance shaft.
Lighting by Tarquin and Sol
Entrance of Siambre Ddu.
Modelling by Steph
Ferns in the entrance.
Lighting by Tarquin and Sol
Moss covered rocks in the entrance.
Fossil imprint of a tree in the entrance.
Modelling by manus de Steph, lighting by Tarquin, Steph and Sol
Fossil log with a very clear branch knot.
The branch knot. The state of preservation is very impressive.
The side passage to the left at the entrance. Just like the chamber itself, this must have been formed as a collapse from below, and is not a water-formed passage. However, it may have formed by water washing out the shale in the underlying Llanelly Shales.
Lighting by Tarquin and Sol
Several fossil logs in the side passage.
Lighting by Tarquin and Steph
Chaotic fossil tree in the side passage.
Modelling by Steph's glove, lighting by Tarquin and Steph
Fossil tree imprint in a shale band.
Lighting by Tarquin and Steph
The way into the chamber is a flat out crawl through the collapse.
Modelling by Steph, lighting by Tarquin, Sol and Steph
Log in the crawl.
Modelling by portions of Tarquin
The last part of the crawl has an enormous fossil tree trunk in the ceiling.
Modelling by Steph, lighting by Tarquin and Steph
Lying beneath the log.
Modelling by Steph, lighting by Tarquin and Steph
Siambre Ddu is an enormous chamber, 25 metres from left to right, 36 metres in length, and around 7 metres high in the middle. This picture has 6 powerful lights, but the manganese stained walls, floor and ceiling drink the light, making it appear very dark. The grey sheen on the ceiling appears to be microbial mats, probably bacteria. The boulders on the floor are mostly quartz conglomerate, and feel very unusual to stand on. We saw a number of bats in here, which flew down through gaps between the boulders. This is likely to be one of the many ways that they make their way into Ogof Draenen; they have never needed to use man-made entrances.
Modelling by Tarquin and Steph, lighting by Tarquin and Steph
Heavily grooved rock, which appears to be a fossil tree.
Formations near the entrance crawl, with a tick coating of microbial mats.
Gold and grey coloured microbial mats. The gold ones are hydrophobic, and the beads of water that gather on them glisten better than gold.
Tree imprints.
Modelling by Tarquin's toe
Rippled flowstone, with a golden edge standing starkly against the manganese.
Two-pronged bristletail (Diplura), which eats the rotting vegetation that makes its way into the cave.
Modelling by Dai Plura
Coloured drips, probably ochre, on manganese stained rocks.
The most impressive tree fossils are the preserved skin texture and enormous log sections of a huge tree trunk, on the northern side of the shakehole. Each oval shaped rock is a part of the tree trunk, which has been partly flattened. The trunk is about 60 cm across.
Modelling by Steph
Trunk segments.
Modelling by Steph's little toe, lighting by Tarquin and Steph
The most beautiful fossil is the skin imprint of a tree, tucked beneath a larger rock. This is likely to be an arborescent lycophyte (a tree version of a club moss), and probably comes from the same tree as the trunk segments. They did not have bark like a modern tree, and are more like a modern palm tree, or pineapple.
Modelling by a rubber coated Steph
Textured tree trunk segment nearby.
Immediately beside it is another fine example of a tree's skin texture. This one has less detail, but appears to be the same tree.
Flowstone formations, made from ochre and manganese. It should be noted that there is no limestone above this; the layers above would have been iron ore deposits and coal measures. Therefore these cannot be calcite formations.
Modelling by Steph
Shiny black flowstone, with streaks of dark blue and green. This looks more like an oil slick than flowstone, or perhaps something out of a horror film.
Rippled gour pools in the flowstone.
Patterns in the flowstone.
Grey formations in the ceiling, which appear to have microbial mats over the top of the black manganese.
Lighting by Tarquin and Steph
Orange and black formations. The orange again appears to be ochre.
Modelling by Steph
Orange gours.
Tucked behind the formation is an inlet, which repeatly sent little burst of water, with a gap in between.
The alcove at the back of the chamber has very dark black formations, which again look more like oil. This part of the chamber also has a visible bed of shale, showing that the cave is formed at the bottom of the Twrch Sandstone Formation.
A stream of orange mud on the southern side of the chamber. This is likely to be red ochre.
Modelling by Steph, lighting by Tarquin and Steph
The entrance to Large Shelter, a very short cave. As we approached the quarry containing the cave, we met a climber who had fallen just over 3 metres when a bolt popped out, fracturing his tibia. The climbers shown here had begun helping him try to hop to the road. I joined in, and we carried him 750 metres down the track back to the cars.
Modelling by Steph and some climbers
Large Shelter had been enlarged by the quarry workers to make it into a useful shelter, and it served us as a place to make a cup of tea. Sadly it sees a lot of untidy visitors, and always has some litter strewn about.
The remains of the Blackwalls caving hut, which was used by Oxford University Caving Club during the exploration of Ogof Draenen.
Modelling by Steph
Looking towards Cwm Llanwenarth from the open land below the former Lamb and Fox pub. Lamb and Fox Chamber in Ogof Draenen sits underneath the field in front of the camera, and Megadrive North and Underworld Series are beneath the right edge of the field. The pub itself sits over the junction of White Arch Passage and Back Passage, close to Tea Junction. In the background are Gilwern Hill (441 metres, the part containing Waterfall Series), Pen y Gadair Fawr (800 metres), Pen Twyn Mawr (658 metres), Pen Gwyllt Meirch (580 metres), Disgwylfa (540 metres), Crug Mawr (550 metres), Sugar Loaf (596 metres), The Skirrid (486 metres), Edmund's Tump (423 metres) and the Blorenge (561 metres, but not the part containing Ogof Draenen).
Former sidings on the Hill's Tramroad. These sit over Anastomosis Passage, Faded Love and Blue Eyes Cryin' in Underworth Series, with Megadrive North ending just beyond them. The Lamb and Fox pub and Pwll Du Adventure Centre can be seen on the left, with the rope climb in the Entrance Series below the adventure centre, and the entrance below the grassy slopes to its right. Waterfall Series ends below the radio mast on Gilwern Hill ahead. Pen Cerrig-calch (701 metres), Table Mountain (451 metres) and Waun Fach (811 metres) are now visible between Gilwern Hill and Pen y Gadair Fawr.
Cutting on the Hill's Tramroad. The camera is over the top of the end of Siambre Ddu Passage, with Siambre Ddu itself being at the far end of the cutting.
Fossil tree imprint in a lump of quartz conglomerate in the cutting.
Pwll Du Quarry, with Hill's Tramroad running along the ledge near the top. Siambre Ddu Passage runs parallel to the quarry, about 30 metres behind it, and the Nunnery is about 60 metres behind the camera. Siambre Ddu itself is in the mouth of the tramroad cutting at the top of the quarry. The stone lined shaft on the left is the top of the balance shaft, which was powered by the stream on the left. The entrance to Balance Shaft Cave is in the gully at the bottom of the quarry below it. The sink that supplies the Black Beetle streamway is in the middle of the quarry, but is currently dry.
Hill's Tramroad has fallen into the quarry, and the path along it is now a very narrow ledge. The tramroad is fenced off on one side and walled off on the other.
Modelling by Steph
The Twrch Sandstone Formation is very visible at the top of the quarry. Two bands have very visible large quartz pebbles.
The top of the balance shaft, which funnels in before you can see the bottom. An empty tram truck would be put onto one of the two carriages that ran up and down the balance shaft, at the top. A truck loaded with limestone would be put into the other carriage at the bottom. Stream water would be directed into the bottom of the empty truck's carriage, until it was heavier than the loaded truck in the other carriage. It would then sink down the shaft, pulling up the full truck with a cable that ran over a pulley at the top. The full truck would be removed from its carriage at the top, the water would be emptied from the carriage at the bottom of the shaft, the empty truck at the bottom would be removed from its carriage and replaced with a full one, an empty truck would be put onto the carriage at the top. The cycle would be repeated, lifting limestone using water power.
Modelling by Steph
The entrance to Balance Shaft Cave at the bottom of the quarry.
Balance Shaft Cave starts very low, filled with sheep and fox scat. At most, it is stooping height. However, it would once have been large enough to fit tram trucks through, before it got filled in with quarry debris.
Modelling by Steph, lighting by Tarquin, Steph and Sol
Metellina merianae cave spider, which appears to be female.
Modelling by Arianwen
Shotholes in the walls show that the quarry workers had enlarged parts of the passage to allow the tram trucks to fit.
Modelling by some grains of sand
Fossil shark dorsal spine, probably a Ctenacanthus.
The only side passage is very short and narrow, but is shown much larger than it is on older surveys. The only other alcoves are full of animal bones.
Crawl from the larger passage into the bottom of the balance shaft. It would have been a good idea to wear proper caving gear here.
Modelling by Steph, lighting by Tarquin, Steph and Sol
Looking up the balance shaft. This is about 20 metres tall.
Lighting by Sol
Black beetle, a devil's coach horse beetle, on the wall of the shaft.
Modelling by a shining shiny dæmon, lighting by Tarquin and Sol
Stal in the balance shaft.
Lighting by Tarquin and Sol
Entrance of Siambre Ddu.
Modelling by Steph
Ferns in the entrance.
Lighting by Tarquin and Sol
Moss covered rocks in the entrance.
Fossil imprint of a tree in the entrance.
Modelling by manus de Steph, lighting by Tarquin, Steph and Sol
Fossil log with a very clear branch knot.
The branch knot. The state of preservation is very impressive.
The side passage to the left at the entrance. Just like the chamber itself, this must have been formed as a collapse from below, and is not a water-formed passage. However, it may have formed by water washing out the shale in the underlying Llanelly Shales.
Lighting by Tarquin and Sol
Several fossil logs in the side passage.
Lighting by Tarquin and Steph
Chaotic fossil tree in the side passage.
Modelling by Steph's glove, lighting by Tarquin and Steph
Fossil tree imprint in a shale band.
Lighting by Tarquin and Steph
The way into the chamber is a flat out crawl through the collapse.
Modelling by Steph, lighting by Tarquin, Sol and Steph
Log in the crawl.
Modelling by portions of Tarquin
The last part of the crawl has an enormous fossil tree trunk in the ceiling.
Modelling by Steph, lighting by Tarquin and Steph
Lying beneath the log.
Modelling by Steph, lighting by Tarquin and Steph
Siambre Ddu is an enormous chamber, 25 metres from left to right, 36 metres in length, and around 7 metres high in the middle. This picture has 6 powerful lights, but the manganese stained walls, floor and ceiling drink the light, making it appear very dark. The grey sheen on the ceiling appears to be microbial mats, probably bacteria. The boulders on the floor are mostly quartz conglomerate, and feel very unusual to stand on. We saw a number of bats in here, which flew down through gaps between the boulders. This is likely to be one of the many ways that they make their way into Ogof Draenen; they have never needed to use man-made entrances.
Modelling by Tarquin and Steph, lighting by Tarquin and Steph
Heavily grooved rock, which appears to be a fossil tree.
Formations near the entrance crawl, with a tick coating of microbial mats.
Gold and grey coloured microbial mats. The gold ones are hydrophobic, and the beads of water that gather on them glisten better than gold.
Tree imprints.
Modelling by Tarquin's toe
Rippled flowstone, with a golden edge standing starkly against the manganese.
Two-pronged bristletail (Diplura), which eats the rotting vegetation that makes its way into the cave.
Modelling by Dai Plura
Coloured drips, probably ochre, on manganese stained rocks.
The most impressive tree fossils are the preserved skin texture and enormous log sections of a huge tree trunk, on the northern side of the shakehole. Each oval shaped rock is a part of the tree trunk, which has been partly flattened. The trunk is about 60 cm across.
Modelling by Steph
Trunk segments.
Modelling by Steph's little toe, lighting by Tarquin and Steph
The most beautiful fossil is the skin imprint of a tree, tucked beneath a larger rock. This is likely to be an arborescent lycophyte (a tree version of a club moss), and probably comes from the same tree as the trunk segments. They did not have bark like a modern tree, and are more like a modern palm tree, or pineapple.
Modelling by a rubber coated Steph
Textured tree trunk segment nearby.
Immediately beside it is another fine example of a tree's skin texture. This one has less detail, but appears to be the same tree.
Flowstone formations, made from ochre and manganese. It should be noted that there is no limestone above this; the layers above would have been iron ore deposits and coal measures. Therefore these cannot be calcite formations.
Modelling by Steph
Shiny black flowstone, with streaks of dark blue and green. This looks more like an oil slick than flowstone, or perhaps something out of a horror film.
Rippled gour pools in the flowstone.
Patterns in the flowstone.
Grey formations in the ceiling, which appear to have microbial mats over the top of the black manganese.
Lighting by Tarquin and Steph
Orange and black formations. The orange again appears to be ochre.
Modelling by Steph
Orange gours.
Tucked behind the formation is an inlet, which repeatly sent little burst of water, with a gap in between.
The alcove at the back of the chamber has very dark black formations, which again look more like oil. This part of the chamber also has a visible bed of shale, showing that the cave is formed at the bottom of the Twrch Sandstone Formation.
A stream of orange mud on the southern side of the chamber. This is likely to be red ochre.
Modelling by Steph, lighting by Tarquin and Steph
The entrance to Large Shelter, a very short cave. As we approached the quarry containing the cave, we met a climber who had fallen just over 3 metres when a bolt popped out, fracturing his tibia. The climbers shown here had begun helping him try to hop to the road. I joined in, and we carried him 750 metres down the track back to the cars.
Modelling by Steph and some climbers
Large Shelter had been enlarged by the quarry workers to make it into a useful shelter, and it served us as a place to make a cup of tea. Sadly it sees a lot of untidy visitors, and always has some litter strewn about.