Glossary of geological terms


Abercriban Oolite / Oolit Abercriban

The lowermost (=oldest) unit of the main Carboniferous Limestone rock succession.

Aberedw Formation / Ffurfiant Aberedw

A succession of sandstones and siltstones laid down during the Ludlow epoch of the Silurian Period.

Aeronian / Aeronaidd

Stage of the Lower Silurian Period. See Silurian timechart.

age / oes

Minor sub-division of geological time, the rocks of which comprise a ‘stage’. See geological timescale.

alluvium / llifwaddod

Sands and gravels deposited by a river on its floodplain.

anticline / anticlin

An upfold of rock at any of a variety of scales from metres to tens of kilometres.  Within the Geopark, there are good examples to be seen at Cribarth and at Bwa Maen beside Dinas Rock. See also syncline.

Arenig Series / Cyfres Arennig

Epoch of the Silurian Period. See Silurian timechart.

Armorica / Armorica

A former micro-continent comprising parts of modern-day France and surrounding territory.  It collided with Laurussia thus causing the Variscan orogeny.

Ashgillian or Ashgill Series / Ashgillaidd or Cyfres Ashgill

Latest epoch of the Ordovician Period. See Ordovician timechart.

Avalonia / Afalonia

A former micro-continent which, as the Iapetus Ocean closed up, collided with the continent of Laurentia during the Silurian and Devonian periods.  The collision gave rise to the Caledonian Orogeny. Avalonia comprised what would later become England and Wales, southern Ireland and parts of Newfoundland and the Low Countries – a piece of the Earth’s crust referred to as the Avalon Composite Terrane.

Avon Group / Grŵp Avon

A sequence of limestones and mudstones at the base of the Carboniferous Limestone. Formerly known as the ‘Lower Limestone Shale(s)’.