Geology
All the rocks underlying the surface are more than 300 million years old, but the coastline as seen today has been much subjected to the effects of coastal and river action and, in places, to events which occurred during the Ice Age.
The oldest igneous and volcanic pre-Cambrian granites outcrop on Ramsey and at the southern tip of the peninsula. Later Cambrian sedimentation produced sandstones, visible on the northern coast of St. Brides Bay (and which were used in the building St David's Cathedral). Subsequent Ordivician fine muds dominate the northern Pembrokeshire coast, but volcanic activity has complicated the whole. The later Silurian period saw the creation of limestone and shale, visible along the southern Marloes peninsula.
Subsequent earth movements, erosion by ice and water, and changes in sea level have further affected what we see today.
Read more about this topic: Pembrokeshire Coast Path