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 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

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. ...

, intensely bioturbated in places. It varies in colour from a pale to a medium blue. 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 south-west to Cardigan Bay at Tywyn.

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 Broad Vein is one of the two major slate veins in Mid Wales that were commercially quarried. Broad Vein rock is generally dense, with few natural joints, so most of the commercial use was for slab and products such as mantlepieces, cisterns and (later) electrical switchboards. Production of roofing slates was relatively rare in Broad Vein quarries. The Broad Vein was quarried in the following locations: * Bryn Eglwys where the Narrow Vein 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 ...

* Abercwmeiddaw quarry, the most commercially successful of the quarries that only worked the Broad Vein. Connected to the Upper Corris Tramway * Cambergi quarry in

Cwm Hengae Cwm Hengae is a valley that runs roughly north-west from the village of Aberllefenni in Wales. The Afon Llefenni river runs along the valley and several slate quarries occupy the valley sides. The Roman road Sarn Helen ran along the valley, conne ...

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 continu ...

which worked from the 14th. century until 2002. Also worked the Narrow Vein. Connected to the Corris Railway * Ratgoed quarry, which mainly worked the Narrow Vein, 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 ...

Maes-y-gamfa quarry 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 ...

a smaller operation, 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 ...

, near Dinas Mawddwy, 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 chains ...

References

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