Glossary of geological terms
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.
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.
Oxwich Head Limestone Formation / Ffurfiant Calchfaen Oxwich Head
Sequence of rocks forming a part of the Pembroke Limestone Group of the Carboniferous Limestone. Formerly known in this area as the Penwyllt Limestone.
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.