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Glossary of geological terms

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MN OP QRSTU VW X Y Z

N

Namurian / Namuraidd

A stage (sub-division) of the Carboniferous Period during which the Marros Group containing the Twrch Sandstone and Bishopston Mudstone was laid down. See Carboniferous timechart.

Neath Disturbance / Cylchfa Ffawtio-plygu Cwm Nedd

Linear zone comprising geological faults and folds stretching from Swansea Bay to Hereford, responsible for the Vale of Neath and evident at Craig y Ddinas (Dinas Rock)

Neogene / Neogen

Name given to the second (younger) of two new periods which replace the Tertiary Period.  It lasted from 23 to 2.6 million years ago and follows the Palaeogene.

O

Old Red Sandstone / Hen Dywodfaen Coch

Traditional name for the sequence of sandstones and mudstones which comprise the Devonian Period and the uppermost Silurian. See geological timescale.

Old Red Sandstone Continent / Cyfandir yr Hen Dywodfaen Coch

Also known as ‘Laurussia’ or ‘Euramerica’ – a continent of the Silurian and Devonian periods which comprised much of modern-day North America, Greenland and Northern Europe.  Named for its distinctive ‘red beds’ of desert sandstones.

oolite / oolit

A limestone consisting of myriad tiny spheres (ooliths) of calcium carbonate.

Ordovician / Ordofigaidd

Geological period which lasted 52 million years from 485 to 443 million years ago. See geological timescale.

Oystermouth Formation / Ffurfiant Oystermouth

Unit of the Carboniferous Limestone formerly known as the Upper Limestone Shale and which includes deposits of a weathered sandy limestone known as ‘rottenstone’ which has been quarried commercially at numerous locations in the Geopark for use as an abrasive and polishing agent.