Carreg Dwfn is a hill four miles southeast of Llandeilo

Llandeilo

Llandeilo is a town in Carmarthenshire, Wales, situated at the crossing of the River Towy by the A483 on a 19th century stone bridge. Its population is 1,731.The town is served by Llandeilo railway station on the Heart of Wales Line.- Early history :...

 and just to the south of the village of Trap

Trap, Carmarthenshire

Trap, or Trapp, is a hamlet in the county of Carmarthenshire in southwest Wales, located on the western border of the Brecon Beacons National Park, around four miles from the town of Llandeilo. Its name often appears as Trapp on maps, though the spelling with a single p is to be preferred...

 in the county of Carmarthenshire

Carmarthenshire

Carmarthenshire is a unitary authority in the south west of Wales and one of thirteen historic counties. It is the 3rd largest in Wales. Its three largest towns are Llanelli, Carmarthen and Ammanford...

, south Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. It lies at the western extremity of the Brecon Beacons National Park and Fforest Fawr Geopark

Fforest Fawr Geopark

Fforest Fawr Geopark was the first Geopark to be designated in Wales having gained membership of both the European Geoparks Network and the UNESCO-assisted Global Network of National Geoparks in October 2005. The Geopark aims to promote and support sustainable tourism and other opportunities to...

. Its summit at 283 metres (928.5 ft) is towards the eastern end of a rocky east-west-aligned ridge.

Geology

The hill is formed from the coarse Twrch Sandstone

Marros Group

The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geographically separate rock sequences of the Pennines and...

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

Namurian

The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age...

 stage of the Carboniferous period. It is defined by
faults to east and west. There are a handful of disused gritstone

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 paper and for grindstones to sharpen blades. "Grit" is...

 quarries on the southern slope of the hill. To its north are large quarries working the Carboniferous Limestone

Carboniferous limestone

Carboniferous Limestone is a term used to describe a variety of different types of limestone occurring widely across Great Britain and Ireland which were deposited during the Dinantian epoch of the Carboniferous period. They were formed between 363 and 325 million years ago...

outcrop which parallels the narrow band of Basal Grit running west to east through the region.

Access

Carreg Dwfn is designated as open country. A public footpath runs around the western, northern and eastern sides.

External links

• images of Carreg Dwfn and surrounding area on Geograph website