The following article is reproduced with the kind permission of UK Fossils Network
The main rocks of the area are of the Devonian period and are mainly mudstones that have been altered into weak slates, they are strongly inclined and to the east of the beach a fault divides the rocks between the Portscatho formation in the west and the Pendower formation to the east.
Running along the back of the bay is a fine example of a raised beach. This was formed relatively recently within the last 2 million years and shows that the sea levels were once higher than at present, this raised beach sits directly upon the Devonian rocks and is a classic example of unconformity, as the rocks that span the period in between (approx. 350 million years) have completely disappeared.
Occasionally after winter storms a submerged forest is uncovered which contains many familiar species of trees, it’s thought that these forests which can be found all over the South West are around 3 thousand years old and show that unlike at the time of the raised beach the sea levels were many metres lower during the ice ages.
Apart from microfossils from the Portscatho rocks there are no fossils to be found in either the cliffs or raised beach, the whole area is protected by SSSI status so please do not hammer or disturb the cliff formations. To collect fossils we need to head to the eastern end of the bay and travel back in time to the Ordovician period.
For anyone interested in the Late Devonian, further East at Carne, the Carne Formation of the Devonian are part of the Givetian stage.
Enthusiasts will find more detailed information at the UK Fossils Network site.
You can also download the text of a free guide, 'A Geological trail between Pendower & Carne', written by John Macadam and published by Cornwall County Council in 1997.