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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 Fferm Halfway

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.