The Narrow Vein Mudstone Formation (commonly known as the Narrow Vein) is an

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geology, geological science associated with the study of stratum, strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) in

Mid Wales Mid Wales ( cy, Canolbarth Cymru or simply ''Y Canolbarth'', meaning "the midlands") or Central Wales refers to a region of Wales, encompassing its midlands, in-between North Wales and South Wales. The Mid Wales Regional Committee of the Senedd ...

. The rock of the formation is silty, homogeneous or finely-laminated

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

. It generally a medium blue colour. This formation has been commercially quarried as

slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...

in several locations along its length. The formation is between and thick and runs from

Dinas Mawddwy Dinas Mawddwy () is a village in the community of Mawddwy in south-east Gwynedd, north Wales. It lies within the Snowdonia National Park, but just to the east of the main A470, and consequently many visitors pass the village by. Its population is ...

south-west to

Cardigan Bay Cardigan Bay ( cy, Bae Ceredigion) is a large inlet of the Irish Sea, indenting the west coast of Wales between Bardsey Island, Gwynedd in the north, and Strumble Head, Pembrokeshire at its southern end. It is the largest bay in Wales. Geograp ...

Tywyn Tywyn (Welsh: ; in English often ), formerly spelled Towyn, is a town, community, and seaside resort on the Cardigan Bay coast of southern Gwynedd, Wales. It was previously in the historic county of Merionethshire. It is famous as the loc ...

Outcrops

The formation is exposed in a number of locations in Mid Wales where glacial valleys cut across it. It is especially visible in the quarries along its length

Commercial quarrying

The Narrow Vein is one of the two major slate veins in Mid Wales that were commercially quarried. Narrow Vein rock is generally more splittable than Broad Vein rock and was often used to make roofing slates. The Narrow Vein was quarried in the following locations: *

Bryn Eglwys Bryn Eglwys quarry was a slate quarry and mine near Abergynolwyn, in Merionethshire (now part of Gwynedd), Wales. More than 300 men worked at the site, making it the principal employer in the area. Two veins of slate, known as the Broad Vein an ...

where the

Broad Vein The Broad Vein Mudstone Formation (commonly known as the Broad Vein, historically known as the Red Vein and in Welsh as Y Faen Goch) is an Ordovician lithostratigraphic group (a sequence of rock strata) in Mid Wales. The rock of the formation is s ...

was also worked, connected to the

Talyllyn Railway The Talyllyn Railway ( cy, Rheilffordd Talyllyn) is a narrow gauge preserved railway in Wales running for from Tywyn on the Mid-Wales coast to Nant Gwernol near the village of Abergynolwyn. The line was opened in 1865Drummond 2015, page 17 ...

* Gaewern and Braichgoch quarries in

Corris Uchaf Corris Uchaf ( en, Upper Corris) is a village lying in the south of the Snowdonia National Park in Gwynedd, Wales. The slate quarries that surround Corris Uchaf are its most prominent feature. Description The village lies in the valley o ...

, connected to the

Upper Corris Tramway The Upper Corris Tramway was a gauge horse-worked tramway that connected the slate quarries around the villages of Corris and Corris Uchaf with the Corris Railway at Maespoeth Junction. It was just over long. History Opening The tramway w ...

Aberllefenni Quarry Aberllefenni quarry is the collective name of three slate quarries, Foel Grochan, Hen Gloddfa (also known as Hen Chwarel) and Ceunant Ddu, located in Cwm Hengae, just to the west of Aberllefenni, Gwynedd, North Wales. It was the longest contin ...

which worked from the 14th. century until 2002. Also worked the Broad Vein. Connected to the

Corris Railway The Corris Railway ( cy, Rheilffordd Corris) is a narrow gauge preserved railway based in Corris on the border between Merionethshire (now Gwynedd) and Montgomeryshire (now Powys) in Mid-Wales. The line opened in 1859 as a horse tramway, runni ...

* Cymerau Quarry, connected to the

Ratgoed Tramway The Ratgoed Tramway (originally known as the Ty Cam branch) was a gauge horse-worked tramway that connected the remote Ratgoed Quarry with the Corris Railway at Aberllefenni. It was long. History Opening Ratgoed Quarry was first opened bef ...

Ratgoed quarry Ratgoed quarry (also known as Alltgoed quarry) was the northernmost of the slate quarries served by the Corris Railway. It is one mile north of Aberllefenni in Gwynedd, Mid Wales, on the western side of Mynydd Llwydiarth. The quarry primarily ...

, which mainly worked the Narrow Vein, connected to the Ratgoed Tramway *

Hendre Ddu quarry Hendre is an old Welsh word for an old house or winter farmhouse (also spelt ). The name may refer to: Places in Wales * Hendre (Bangor electoral ward), an electoral division in Bangor * Hendre, Llanddyfnan, an area of Llandyfnan, Anglesey * Hen ...

a smaller operation connected to the

Hendre-Ddu Tramway The Hendre-Ddu Tramway was a narrow gauge industrial railway built in 1874 in Mid-Wales to connect the Hendre-Ddu slate quarry to Aberangell station on the Mawddwy Railway. It consisted of a main line long and several branch lines and spurs ...

* Gartheiniog quarry, also connected to the Hendre-Ddu Tramway *

Minllyn quarry Minllyn quarry was a slate quarry near Dinas Mawddwy in Wales that opened before 1793 and continued working intermittently until 1925. The quarry is located on the western flank of Foel Dinas. Geology Three parallel veins of Ordovician slate ...

connected to the

Mawddwy Railway The Mawddwy Railway was a rural line in the Dyfi Valley in mid-Wales that connected Dinas Mawddwy with a junction at railway station on the Newtown and Machynlleth Railway section of the Cambrian Railways. Despite being only 6 miles 63 chain ...

References

{{Reflist Ordovician System of Europe Upper Ordovician Series Rock formations of Wales Slate industry in Wales