Cynwyd Forest Quarry

Overview

Cynwyd Forest Quarry is a very small disused quarry beside a track in the Cynwyd Forest near Corwen, notified as a Site of Special Scientific Interest in 1983 and covering less than a fifth of a hectare. It is there for what it cut through rather than what it produced: a section in the Late Ordovician siltstones and mudstones of the Dolhir Formation, yielding a rich shelly fauna of brachiopods together with trilobites, bivalves, bryozoans, crinoids and cystoids.

History

The industrial history of this quarry is not recorded in anything read for this account. No owner, no dates, no output, no workforce; what is documented is a section beside a forest track and the fossils in it. The site is sometimes referred to in the literature as Bwlch y Gaseg, and lies very close to the area of that name. It was notified as a Site of Special Scientific Interest on 16 May 1983, for geology and palaeontology, and covers 0.18 hectares — about four tenths of an acre. It was described by Rushton and others in their survey of Cambrian to Ordovician stratigraphy for the Joint Nature Conservation Committee, and the trilobite that dominates its fauna was described from north Wales by Price in 1982.

Geology

The quarry exposes Late Ordovician micaceous siltstones and mudstones of the Dolhir Formation, of the Ashgill Series and the Rawtheyan Stage — the very end of the Ordovician, shortly before the glaciation that closed the period. The rock yields a rich shelly fauna dominated by brachiopods. Trilobites are represented by several genera, but the fauna is dominated by Gravicalymene arcuata, the species Price described in 1982; Illaenus davisii, Remopleurides, two species of Pseudosphaerexochus, Calyptaulax and Tretaspis are also present. Alongside them are bivalves, the bryozoans Pinnatoporella carinata, Phylloporina and Graptodictya, the brachiopod Leptaena, the cephalopod Zitteloceras costatum, the crinoid Cupulocorona rugosa, and the cystoids Regulaecystis inconstans and Dendrocystoides. Most of these are illustrated in the Palaeontological Association's field guide to fossils of the Upper Ordovician, which is a fair indication of how representative the section is.

Geological setting: Sedimentary Beds and Seams (surviving physical example)

Workings

A very small quarry beside a track in the forest — the notified area is 0.18 hectares. Nothing read for this record describes its faces, its depth, its plant or what the stone was taken for.

Closure

No closure date has been established. The quarry was disused by the time of its notification in 1983 and nothing consulted here narrows it further.

What remains

A designated Site of Special Scientific Interest of 0.18 hectares within forestry, beside a track. The faces were photographed in July 2021 and the section remains accessible and worth study; it is the exposure rather than any quarry structure that is protected.

The quarry faces beside the forest track, which are the reason for the designation. Nothing read for this record describes a surviving quarry structure.

Nearby mines

• Craig-y-Mwyn Mine — 12.9 km S, Powys

Straight-line distance, within 15 km. Show on the map.

Recorded claims

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

• Cynwyd Forest Quarry is a Site of Special Scientific Interest located beside a track within the Cynwyd Forest near Corwen, Denbighshire, notified on 16 May 1983 for geology and palaeontology, covering 0.18 ha at grid reference SJ 09135 39969. ¹
• The quarry exposes Late Ordovician micaceous siltstones and mudstones of the Dolhir Formation, of the Ashgill Series and Rawtheyan Stage, which yield a rich shelly brachiopod fauna. ¹
• Trilobites are represented by several genera although the fauna is dominated by Gravicalymene arcuata Price, 1982; bivalves, bryozoans and various Echinodermata, including crinoids and cystoids, are also present. ¹
• The site is sometimes referred to in the literature as 'Bwlch y Gaseg', and is in very close proximity to the area of the same name. ¹
• The quarry faces were photographed in July 2021. ²

Photographs & further reading

Sources

1. (secondary) Cynwyd Forest Quarry — Wikipedia
2. (observational) Cynwyd Forest Quarry, July 2021 (photograph) — Wikimedia Commons

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