Geology determined the origins and foundation of Pembroke, which is situated on a ridge of hard Carboniferous limestone (coloured light grey on map), and is surrounded by the older but softer Devonian shales and sandstones (coloured orange and pale pink).

Geology of Pembrokeshire CastlePromentory250.jpg Pembroke castle and surrounds (aerial view)

The historic core of Pembroke is constructed on the low, east-west aligned limestone ridge, to the north and west of which lies the tidal (but now dammed) Pembroke River and to the south an area of marshy land (now partly reclaimed and used as car parks), called the Commons. Pembroke Castle, on the western end of this ridge, dominates the whole of the town which developed in stages eastwards from the castle, along one long main street. The town is situated at the head of one of the many creeks of the Milford Haven waterway, a drowned river valley known as a ria and now designated an SSSI (Site of Special Scientific Interest) and also a Marine Special Area of Conservation.

The hard nature of the limestone provided the prominent outcrop for the construction of the castle. Because limestone is also soluble in water, the presence of caves enabled early peoples to settle here.

A cross section, from north to south, through Pembroke rock and the hills on either side


South Pembrokeshire is of international importance geologically. In the carboniferous seas 350 million years ago there was abundant life when this area lay beneath a tropical sea.

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Fossil evidence can be found in the lower limestone shales - crinoids (coral-like plants) on the right, and brachiopods (shell fish) in the centre photograph.


Take a look at Pembroke's nearby coastline: for example in the rocks at beach level around Stackpole Quay where you will see ample evidence of these early life forms in the numerous fossils in the limestone cliffs.


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The above photographs show Pembroke Story members and Millponds Action Group volunteers combining to learn more about Geology with Sid Howells, our local expert geologist, and who offers field trips along the South Pembrokeshire coast.

Geology events are organised each summer by the Pembrokeshire National Park and further information can be found here.