Penylan Quarry

Overview

Penylan Quarry worked the outcrop of Silurian mudstone on Pen-y-lan hill in Cardiff — the oldest rocks in the city — for building stone. It has not been quarried since the nineteenth century, and it is remembered now for what the quarrymen exposed rather than for what they took away: a rich shelly fauna of brachiopods, corals, graptolites and trilobites that made it one of the most important fossil sites in Wales. It is a Site of Special Scientific Interest.

History

That Silurian rocks exist at Pen-y-lan hill and in its neighbourhood was made known as long ago as 1861, by Norman Glass, who collected a number of fossils from the quarry. The outcrop was worked for building stone, and the working itself did not outlast the nineteenth century.

Its afterlife has been geological. The quarry became well known for the quality of its Silurian fossils, including complete examples of trilobites such as Encrinurus, and Calymene from Penylan is among the Silurian trilobites held by Amgueddfa Cymru. The site was described in the scientific literature — a paper on the Silurian district of Rhymney and Pen-y-lan was read to the Geological Society in 1879 — and it is now protected as a Site of Special Scientific Interest for its palaeontology. Part of it was lost when a major road was built across the ground, leaving the remainder protected.

Geology

The quarry exposes Silurian mudstone, the oldest rock in Cardiff, at an outcrop that rises through the much younger cover of the surrounding city. The rock is a marine mudstone crammed with a shelly fauna — brachiopods, corals, graptolites and trilobites — laid down in a shallow sea, and it is the fossils rather than any mineral content that give the site its standing. Complete trilobites of the genus Encrinurus have come from here, and Calymene from Penylan is among the Welsh Silurian material in the national collection. This is sedimentary rock worked as bulk building stone; there is no mineralisation and no vein.

Geological setting: Sedimentary Beds and Seams (historical documentary reference)

Workings

A surface quarry on the hill at Pen-y-lan, worked into the Silurian outcrop for building stone. Its plan, its depth and how it was worked are not recorded, and no figures for output or workforce survive.

Closure

The quarry has not been worked since the nineteenth century. No source here gives a closure date or a reason; the ordinary explanation for a small urban building-stone quarry of this kind is that the city grew over it and better stone came in by rail, but that is not stated anywhere read and is not asserted here.

What remains

Protected as a Site of Special Scientific Interest, and partly gone: the site became partly inaccessible when a major road was built, though the remainder is now protected. It remains a notable palaeontological locality.

The quarried faces of the Silurian outcrop, so far as they survive the road that took part of the site. Nothing on record describes any quarry building or structure.

Related mines

• Rumney Quarry — The two Cardiff quarries cut the same thing: a single inlier of Silurian rock breaking through the younger cover in the eastern suburbs, which the Geological Survey describes as cropping out at Rumney and Pen-y-lan together. Both were worked for stone in the nineteenth century and both are now Sites of Special Scientific Interest for what they exposed.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• Penylan Quarry is a quarry and a Site of Special Scientific Interest in Penylan, Cardiff, and a notable palaeontological site containing fossil trilobites and Silurian brachiopods. ¹
• Penylan quarry was well known for its Silurian fossils, including complete examples of trilobites such as Encrinurus; Calymene from Penylan Quarry is among the Silurian trilobites of Wales held in the national collection. ²
• The site became partly inaccessible when a major road was built, although the remainder of the site is now protected. ²

Photographs & further reading

Sources

1. (secondary) Penylan Quarry — Wikipedia
2. (secondary) Trilobites in Wales — Amgueddfa Cymru — Museum Wales

Record created: 4 September 2026 · Last researched: 5 September 2026