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Glossary of geological terms

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Raglan Marl Group / Grwp Marl Rhaglan

Former name for the Raglan Mudstone Formation

Raglan Mudstone Formation / Ffurfiant Carreg Laid Raglan

A thick succession (up to 1100m) of mudstones and siltstones laid down during the Pridoli Stage of the Silurian Period.

Redhill & Slade Beds / Gwelyau Redhill a Slade

A succession of mudstones and sandstones laid down during the Ashgillian Epoch of the Ordovician Period.

Red Marl Group / Grwp y Marl Coch

Former name for the Raglan Mudstone Formation

Red Sandstone Formation / Ffurfiant y Tywodfaen Coch

Former name for the Brownstones and Senni Formations and the uppermost part of the St Maughan’s Formation.

Rhuddanian / Rhuddanaidd

Lowermost stage of the Silurian. See Silurian timechart.

rottenstone / carreg bwdr

Weathered limestone which was once quarried for use as an abrasive.  The removal by natural processes of the calcium carbonate from the rock left a pumice-like material composed of silica.  The largest deposits were worked in the C19th just to the northwest of Cribarth.