Glossary of geological terms
ABCDEFGHI J KL
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.
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.