The Clwyd Limestone Group is a

stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features ( facies) that characteriz ...

(a defined sequence of rock layers) of Chadian to Brigantian age (

Lower Carboniferous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is sit ...

) found in north

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 forms part of the Carboniferous Limestone Supergroup. Its most extensive outcrop is along the length of the

Clwydian Range The Clwydian Range (; also Clwydian Hills or Clwyds) is a series of hills in the north-east of Wales that runs from Llandegla in the south to Prestatyn in the north; the highest point is Moel Famau. The range forms the north-western part o ...

, immediately to the east of its crest, between

Llandegla Llandegla () or Llandegla-yn-Iâl () is a village and community in the county of Denbighshire in Wales. In the 2011 census, the community had a population of 567. Name The village's name is Welsh for the "Parish of Saint Tecla", which hon ...

and

Prestatyn Prestatyn (; ) is a seaside town and community in Denbighshire, Wales. Historically a part of Flintshire, it is located on the Irish Sea coast, to the east of Rhyl. Prestatyn has a population of 19,085. Origin of name The name Prestatyn d ...

. A further though more fragmented outcrop extends in an arc along the western margins of the

Vale of Clwyd The Vale of Clwyd () is a tract of low-lying ground in the county of Denbighshire in north-east Wales. The Vale extends south-southwestwards from the coast of the Irish Sea for some 20 miles (about 30 km) forming a triangle of low ground bo ...

north from Rhyd-y-meudwy, west of

Ruthin Ruthin ( ; ) is a market town and community in Denbighshire, Wales, in the south of the Vale of Clwyd. The town, castle and St Peter's Square lie on a hill, skirted by villages such as Pwllglas and Rhewl. The name comes from the Welsh ''rhud ...

and then northwest to meet the coast at

Llanddulas Llanddulas is a village in Conwy county borough, Wales, midway between Old Colwyn and Abergele and next to the North Wales Expressway in the community of Llanddulas and Rhyd-y-Foel. The village lies beneath the limestone hill of Cefn-yr-Og ...

. It is prominently exposed at the

Great Orme The Great Orme () is a limestone headland on the north coast of Wales, north-west of the town of Llandudno. Referred to as ''Cyngreawdr Fynydd'' by the 12th-century poet Gwalchmai ap Meilyr, its English name derives from the Old Norse word for ...

and

Little Orme The Little Orme () is a headland in Llandudno, Wales. It is in height. It is one of two headlands situated at either end of Llandudno Bay, the other larger headland used by tourists is the Great Orme. The Little Orme has public footpaths and tw ...

near

Llandudno Llandudno (, ) is a seaside resort, town and community (Wales), community in Conwy County Borough, Wales, located on the Creuddyn peninsula, which protrudes into the Irish Sea. In the 2021 United Kingdom census, 2021 UK census, the community � ...

and again in three areas of eastern and southern

Anglesey Anglesey ( ; ) is an island off the north-west coast of Wales. It forms the bulk of the Principal areas of Wales, county known as the Isle of Anglesey, which also includes Holy Island, Anglesey, Holy Island () and some islets and Skerry, sker ...

, together with a small area to the south of the

Menai Strait The Menai Strait () is a strait which separates the island of Anglesey from Gwynedd, on the mainland of Wales. It is situated between Caernarfon Bay in the south-west and Conwy Bay in the north-east, which are both inlets of the Irish Sea. The s ...

between Bangor and

Y Felinheli Y Felinheli (), formerly known in English as Port Dinorwic, is a village and community beside the Menai Strait ( or ''Afon Menai'') between Bangor and Caernarfon in Gwynedd, northwest Wales. History Toponymy Etymologically, its name comes f ...

. The outcrop also extends southwards from Llandegla to form an impressive scarp at Creigiau Eglwyseg north of

Llangollen Llangollen () is a town and community (Wales), community, situated on the River Dee, Wales, River Dee, in Denbighshire, Wales. Its riverside location forms the edge of the Berwyn range, and the Dee Valley section of the Clwydian Range and Dee Val ...

and south again, to the west of

Oswestry Oswestry ( ; ) is a market town, civil parish and historic railway town in Shropshire, England, close to the England–Wales border, Welsh border. It is at the junction of the A5 road (Great Britain), A5, A483 road, A483 and A495 road, A495 ro ...

Llanymynech Llanymynech is a village and former civil parish straddling the Wales-England border, border between Powys, Wales, and Shropshire, England, about north of the Welsh town of Welshpool. The name is Welsh language, Welsh for "Llan (placename), L ...

Hill on the

Powys Powys ( , ) is a Principal areas of Wales, county and Preserved counties of Wales, preserved county in Wales. It borders Gwynedd, Denbighshire, and Wrexham County Borough, Wrexham to the north; the English Ceremonial counties of England, ceremo ...

Shropshire Shropshire (; abbreviated SalopAlso used officially as the name of the county from 1974–1980. The demonym for inhabitants of the county "Salopian" derives from this name.) is a Ceremonial counties of England, ceremonial county in the West M ...

border. In Anglesey, it comprises the Loggerheads Limestone Formation and overlying Cefn Mawr Limestone Formation. These are supplemented at the Great Orme by an underlying Llanarmon Limestone Formation and an overlying Red Wharf Limestone Formation, both of which are

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite (see Dolomite (rock)). An alternative name sometimes ...

, at least in part. In the Clwydian Range, a lowermost Foel Formation is succeeded in turn by the Llanarmon Limestone, Leete Limestone, Loggerheads Limestone and Cefn Mawr Limestone formations. These are capped by the limestones and sandstones of the Minera Formation which completes the sequence. The outcrop in the west of the Vale of Clwyd is similar but narrower and lacking the Foel Formation. The outcrop south of Llandegla comprises only the Leete, Cefn Mawr and Minera units. There is a small faulted

inlier An inlier is an area of older rocks surrounded by younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. Faulting or folding may also contribute to the o ...

of the Clwyd Limestone around

Ffrith Ffrith is a small village in the community of Llanfynydd in Flintshire, north-east Wales. Name The name Ffrith (the Welsh double "f" is pronounced simply as "f") reflects a spelling and pronunciation particular to Flintshire: it is derived f ...

to the northwest of

Wrexham Wrexham ( ; ) is a city status in the United Kingdom, city in the North East Wales, north-east of Wales. It lies between the Cambrian Mountains, Welsh mountains and the lower River Dee, Wales, Dee Valley, near the England–Wales border, borde ...

and a smaller

outlier In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to a variability in the measurement, an indication of novel data, or it may be the result of experimental error; the latter are ...

of the Clwyd Limestone just to the west of

Corwen Corwen is a town and community in the county of Denbighshire in Wales. Historically, Corwen was part of the county of Merionethshire. Corwen stands on the banks of the River Dee beneath the Berwyn mountains. The town is situated west of Llang ...

References

{{Reflist Geology of Wales Limestone groups of the United Kingdom Carboniferous Wales Carboniferous System of Europe Mudstone groups Sandstone groups

See also

References