The term 'Pebidian' (along with Dimetian) was coined by geologist Henry Hicks in 1876 and published in a scientific paper in the Quarterly Journal of the Geological Society in the following year.
[1] These rocks are exposed in the St David's peninsula in northwestern Pembrokeshire.
One outcrop stretches east from Treginnis, wrapping around the north of St David's to Treglemais.
The supergroup comprises at its base the Treginnis, Treglemais and Penrhiw 'Groups' of the Lower Pebidian which include trachytic and andesitic tuffs and halleflinta.
Uppermost i.e. youngest is the Ogofgolchfa Group which includes slates and tuffs.