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 characterize ...

(a defined sequence of rock layers) of Chadian to Brigantian age ( Lower Carboniferous) found in north

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

. It forms part of the Carboniferous Limestone Supergroup. Its most extensive outcrop is along the length of the Clwydian Range, immediately to the east of its crest, between Llandegla 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, History Prehistory There is evidence that ...

. A further though more fragmented outcrop extends in an arc along the western margins of the Vale of Clwyd north from Rhyd-y-meudwy, west of

Ruthin Ruthin ( ; cy, Rhuthun) is a market town and community in Denbighshire, Wales, in the south of the Vale of Clwyd. It is Denbighshire's county town. The town, castle and St Peter's Square lie on a hill, skirted by villages such as Pwllglas an ...

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-Ogo ...

. It is prominently exposed at the Great Orme and

Little Orme The Little Orme ( cy, Rhiwledyn, also known as Trwyn y Fuwch, Trwyn y Gogarth and Y Gogarth Fach) is in height, and is a HuMP (having a minimum Hundred Metre Prominence). It is one of two headlands situated at either end of Llandudno Bay, in C ...

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 2011 UK census, the community – which includes Gogarth, Pe ...

and again in three areas of eastern and southern

Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a Local government in Wales, principal area known as the Isle of Anglesey, that includes Holy Island, Anglesey, Holy Island across the narrow Cymyran Strai ...

, together with a small area to the south of the

Menai Strait The Menai Strait ( cy, Afon Menai, the "river Menai") is a narrow stretch of shallow tidal water about long, which separates the island of Anglesey from the mainland of Wales. It varies in width from from Fort Belan to Abermenai Point to from ...

between Bangor and Y Felinheli. The outcrop also extends southwards from Llandegla to form an impressive scarp at Creigiau Eglwyseg north of Llangollen 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 Welsh border. It is at the junction of the A5, A483 and A495 roads. The town was the administrative headquarters of the Boroug ...

to Llanymynech Hill on the

Powys Powys (; ) is a Local government in Wales#Principal areas, county and Preserved counties of Wales, preserved county in Wales. It is named after the Kingdom of Powys which was a Welsh succession of states, successor state, petty kingdom and princi ...

Shropshire Shropshire (; alternatively Salop; abbreviated in print only as Shrops; demonym Salopian ) is a landlocked historic county in the West Midlands region of England. It is bordered by Wales to the west and the English counties of Cheshire to ...

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. An alternative name sometimes used for the dol ...

, 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 of the Clwyd Limestone around Ffrith to the northwest of

Wrexham Wrexham ( ; cy, Wrecsam; ) is a city and the administrative centre of Wrexham County Borough in Wales. It is located between the Welsh mountains and the lower Dee Valley, near the border with Cheshire in England. Historically in the county ...

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 is 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 Llan ...

References

{{Reflist Geology of Wales Limestone formations of the United Kingdom Carboniferous Wales Carboniferous System of Europe

See also

References