Abandoned 'slate' quarry, Abereiddi Bay, Pembrokeshire

Originally uploaded for the GuesswhereUK group. Photo has been replaced with slightly more extensive, uncropped version.

This is the back-wall of the abandoned 'slate' quarry, the flooded section of which is now the Blue Lagoon at Abereiddi bay, Pembrokeshire.

The rock is not true slate (a metamorphic rock) but thinly bedded black shales (Caerhys Shale) which span the Llanvirnian-Llandeilian junction in the Ordovician. Certain bedding planes towards the right-hand side are particularly rich in the graptolite zone fossil Didymograptus murchisoni.

Thousands of people each year see this, either walking past it or attending diving or coasteering (horrible word!) events in the Blue Lagoon.