Clarach Bay just north of Aberystwyth is a 1st class exposure of Silurian rocks on the seashore. The rocks are mudstones, grits and sandstones deposited on a deep sea floor, 428-443 million years ago. The rocks are folded and faulted and contain some fossils mainly rather amorphous corals.

Photo: Glacial deposit in the cliff. The upper section appears to be wind-blown sand, beneath that fluvio-deposited gravel, beneath that sand, and below that glacial till.