Glossary of geological terms


Late Devensian Glaciation / Rhewlifiant Defensaidd Diwethaf

The cold period between 26,000 years ago and about 15,000 years ago which marked the height of the last Ice Age.  Otherwise known as the Dimlington Stadial.

Laurasia / Lawrasia

A former continent comprised of the modern-day continents of North America, Europe and Asia.

Laurentia / Lawrensia

A former continent during Cambrian and Ordovician times which comprised much of modern-day North America and Greenland.  Laurentia subsequently collided with Baltica to form Laurussia.

Laurussia / Lawrwsia

See ‘Old Red Sandstone Continent’

limestone / calchfaen

Any rocks composed largely of calcium carbonate or magnesium carbonate (dolomitic limestone).  Limestones are highly variable in nature.

limestone pavement / palmant calchfaen

Generally flat-lying exposure of limestone bedrock which has, to a greater or lesser degree, been weathered into distinct blocks (clints) separated by fissures (grikes). The grikes often afford shelter to a diverse range of plants. A pavement is formed by the action of weakly acidic water dissolving the rock along lines of weakness.

Little Ice Age / Oes Ia Fach

Period from the 16th to the 19th century when the climate of NW Europe was notably colder.

Llandeilan or Llandeilo Series / Cyfres Llandeilo

Epoch of the Silurian Period. See geological timescale.

Llandoverian or Llandovery Series / Cyfres Llanymddyfri

Epoch of the Silurian Period comprising the Rhuddanian, Aeronian and Telychian stages. See geological timescale.

Llandyfan Limestone / Calchfaen Llandyfan

One of the limestones comprising the main Carboniferous Limestone.

Llanelly Formation / Ffurfiant Llanelli

Dolomitic limestone found between the Abercriban Oolite and the Dowlais Limestone within the main Carboniferous Limestone.

Llangammarch Formation / Ffurfiant Llangamarch

Set of mudstones of Wenlock age within Silurian Period.

Llanvirnian or Llanvirn Series / Cyfres Llan-fyrn

Epoch of the Ordovician Period. See geological timescale.

Llety Beds / Gwelyau Llety

Succession of rocks laid down during the Ludlow Epoch of the Silurian Period.

Loch Lomond Stadial / Is-gyfnod Rhewlifol Loch Lomond

The cold period which marked the end of the Pleistocene Epoch and occurred between 11,500 and 10,000 years ago after several thousand years of warming climate and during which glaciers briefly returned to Fforest Fawr.

Lower Coal Measures / Cystradau Glo Isaf

Traditional subdivision of the Carboniferous Period. See geological timescale.

Lower Devonian / Defonaidd Isaf

See geological timescale.

Lower Limestone Shale(s) / Sial(au) Calchfaen Isaf

Set of limestones and mudstones which occur at the base of the main Carboniferous Limestone. Now known as the Avon Group.

Ludlovian or Ludlow Series / Cyfres Llwydlo

Epoch of the Silurian Period during which the sandstones, mudstones and siltstones of the Cae’r Mynach, the Hafod Fawr, Cwm Craig Ddu and other formations were laid down. See geological timescale.