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Glossary of geological terms

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Hafod Fawr Formation / Ffurfiant Hafod Fawr

A succession of sandstones, siltstones and mudstones laid down during the Ludlow Epoch of the Silurian Period. It includes the Cwar Glas Member which contains a number of thick sandstone beds.

Halfway Farm Formation / Ffurfiant Halfway Farm

A succession of mudstones laid down during the Wenlock Epoch of the Silurian Period.

Hirnantian / Hirnantaidd

Uppermost stage of the Ordovician Period. See Ordovician timechart.

Holocene / Holosen

The current epoch which began around 11,500 years ago. See Quaternary timechart.

Honeycombed Sandstone / Tywodfaen Dil Mel

A sandy limestone deposited during the Carboniferous Period.