Carreg Dwfn (also referred to as Careg Dwfn and Carregydwfn and referred to also as Careg-y-dwfan ) is a hill four miles southeast of

Llandeilo Llandeilo () is a town and Community (Wales), community in Carmarthenshire, Wales, situated where the River Towy is crossed by the A483 road, A483 on a 19th-century stone bridge. At the 2021 United Kingdom census, 2021 census the community had ...

and just to the south of the village of Trap in the county of

Carmarthenshire Carmarthenshire (; or informally ') is a Principal areas of Wales, county in the South West Wales, south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. ...

, south

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

. It lies at the western extremity of the

Brecon Beacons National Park Brecon Beacons National Park, officially named Bannau Brycheiniog National Park (), is a National parks of the United Kingdom, national park in Wales. It is named after the Brecon Beacons (), the mountain range at its centre. The national park ...

and

Fforest Fawr Geopark Fforest Fawr Geopark is a Geopark in the Brecon Beacons National Park, south Wales. It is the first designated Geopark in Wales having gained membership of both the European Geoparks Network and the UNESCO-assisted Global Network of National G ...

. Its summit at is towards the eastern end of a rocky east-west-aligned ridge.

Geology

The hill is formed from the coarse

Twrch Sandstone The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period (geology), Period in South Wales. These rocks were formerly known as the Millstone Grit, Millstone Grit Series but are now distinguish ...

(formerly known as the Basal Grit) laid down during the

Namurian The Namurian is a stage in the regional stratigraphy of northwest Europe, with an age between roughly 331 and 319 Ma (million years ago). It is a subdivision of the Carboniferous system or period, as well as the regional Silesian series. The Na ...

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Carboniferous period The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the Permian Period, Ma. It is the fifth and penultimate perio ...

. It is defined by faults to east and west. There are a handful of disused

gritstone Gritstone or grit is a hard, coarse-grained, siliceous sandstone. This term is especially applied to such sandstones that are quarried for building material. British gritstone was used for millstones to mill flour, to grind wood into pulp for ...

quarries on the southern slope of the hill. Quarrying rights at these sites were stopped by the

Brecon Beacons National Park Authority Brecon Beacons National Park, officially named Bannau Brycheiniog National Park (), is a national park in Wales. It is named after the Brecon Beacons (), the mountain range at its centre. The national park includes the highest mountain in South ...

in 2008. To its north is the large Craigyrodyn Quarry which worked the Carboniferous Limestone outcrop which parallels the narrow band of Twrch Sandstone running west to east through the region.

Glacial striae Glacial striations or striae are scratches or gouges cut into bedrock by glacial abrasion. These scratches and gouges were first recognized as the result of a moving glacier in the late 18th century when Swiss alpinists first associated them w ...

on rock surfaces high on the hill record that during the ice age, glacial ice travelled obliquely across it towards the southwest though lower down, to the south, the ice is recorded as moving more or less from east to west.Strahan, A. et al. 1907 ''The Geology of the South Wales Coalfield Part VII: the country around Ammanford'' (memoir to sheet 230 of the Geological Survey) HMSO, London p199

Access

Carreg Dwfn is designated as open country under the provisions of the CRoW Act 2000. Public footpaths run around the western, northern and eastern sides.

External links

images of Carreg Dwfn and surrounding area on Geograph website

References

{{coord, 51.8382, -3.9530, type:mountain_region:GB, display=title Mountains and hills of Carmarthenshire Black Mountain (range)