Broad Vein Mudstone Formation
Stratigraphic range: Hirnantian Age
The Abercwmeiddaw quarry in Corris Uchaf which quarried the Broad Vein
TypeGroup
Unit ofAbercorris Group
UnderliesNarrow Vein Mudstone Formation
OverliesNod Glas Formation
Lithology
PrimaryMudstone
OtherSlate
Location
Coordinates52°39′48″N 3°50′43″W / 52.6632°N 3.8453°W / 52.6632; -3.8453
RegionMid Wales
CountryWales

The Broad Vein Mudstone Formation (commonly known as the Broad Vein, historically known as the Red Vein[1] 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 silty mudstone, intensely bioturbated in places. It varies in colour from a pale to a medium blue. This formation has been commercially quarried as slate in several locations along its length. The formation is between 400 metres (1,300 ft) and 560 metres (1,840 ft) thick and runs from Dinas Mawddwy south-west to Cardigan Bay at Tywyn.[2]

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.[3]

The Broad Vein was quarried in the following locations:

References

  1. "Broad Vein Mudstone Formation". BGS on-line lexicon of rock units. British Geological Survey. Retrieved 6 January 2020.
  2. "Broad Vein Mudstone Formation". BGS on-line lexicon of rock units. British Geological Survey. Retrieved 11 September 2019.
  3. Richards, Alun John (1999). The Slate Regions of North and Mid Wales and Their Railways. Gwasg Carreg Gwalch. ISBN 0-86381-552-9.
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