St Bride's Bay

St Brides Bay (Welsh: Bae Sain Ffraid) is a rocky bay inlet in western Pembrokeshire, West Wales.

Either Skomer Island or the mainland extremity of Wooltack Point at the western end of the Marloes Peninsula marks the southern limit of the bay whilst its northern limit is marked by Ramsey Island off St David's Head. The mouth of the bay is around 7 miles (12 km) wide; the bay extends some 10 miles (16 km) eastwards from this line.

The northern and southern shores of the bay are mainly rocky in nature, backed by cliffs up to 250 feet in height. Its eastern shore comprises a series of large and small sandy beaches between rocky sections.

The geological exposures around the bay reveal great complexity with considerable folding and faulting of the strata. The cliffs of its southern shore are formed from sandstones of Ordovician and Devonian age together with a suite of both intrusive and extrusive igneous rocks, some of which are Precambrian in age. Those in the north comprise a series of Precambrian and Cambrian age rocks of both sedimentary and igneous origin. In contrast, the eastern shore is formed from the more readily eroded rocks of Carboniferous age. These are largely the sandstones and mudstones of the Coal Measures but include a small section of shales and sandstones assigned to the Millstone Grit Series. Contorted coal seams within the Coal Measures were once worked though the Pembrokeshire Coalfield was never of major economic importance.

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