Geology

Geology is the study of planet earth - the materials it is made of, the processes that act on those materials, the products formed, and the history of the planet and its life forms since its origin.

Pembrokeshire displays a greater variety of rocks and scenery than any equivalent area in Britain. There are over 250 miles of coastal and estuarine cliff and foreshore exposures around the County, as well as numerous inland localities where rocks and landforms can be studied.

Since the beginnings of the science of geology, Pembrokeshire has been a prescribed destination for anyone with an interest in the subject.

The oldest surviving rocks on Earth would have been formed about 600 million years after it was created (around 4,100 million years ago). However the oldest rocks in Pembrokeshire were not formed until around 600 million years ago when volcanic eruptions occurred. The oldest fossil plants are of Silurian age, some 415 million years old.

All the rocks now found in Pembrokeshire were formed before the end of the Carboniferous Period (some 290 million years ago). Rocks younger than this have been lost, principally due to weathering and erosion, particularly marine erosion towards the end of the Cretaceous Period (around 80 million years ago) when the sea level was relatively high.

The land masses that today form Britain and North America were once joined together. They drifted apart around 60 million years ago to create the Atlantic Ocean, which is now 3,500 km wide. At the same time the rocks of Pembrokeshire were lifted out of the sea and a drainage system was established on a relatively even cover of marine sediments that sloped gently southwards. The streams and rivers rapidly cut through this material and began to dissect the solid rocks underneath.

The last ice age occurred around 18,500 years ago and the surface of Pembrokeshire was scraped clean of vegetation and soil by advances of the Irish Sea Ice Sheet, which was pushed southwards by glaciers moving out of the mountains of Scotland, the Lake District, and north and mid Wales. At times the ice cover melted away and old river channels were deepened by the flow of meltwater.