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Landscape and geology

As with the rest of Britain, the geological events that initially shaped Carmarthenshire occurred hundreds of millions of years ago, south of the equator and beneath warm tropical seas. For the past 425 million years, the continental plate, on which we stand, has been drifting imperceptibly northwards. For the most part, the exposed rocks of Carmarthenshire are sedimentary and consist largely of a mixture of shales, conglomerates, sandstones and mudstones, with Millstone Grit and Carboniferous Limestone forming the northwestern rim of the South Wales coalfield, which extends into Carmarthenshire in the southeast of the county, but which is also exposed in the sea cliffs running westward from Pendine towards Pembrokeshire.

Almost the whole of the county is hilly or mountainous, the exception being the southern coastal fringes. On its eastern borders, abutting the county of Neath-Port Talbot and Swansea, rise the imposing range of the Mynydd Du (the Black Mountains) and the westernmost part of the Brecon Beacons, where the county’s ‘top’ can be found in the shapely form of Fan Foel, standing at a proud 781m (2562ft). These north facing escarpments are formed from Old Red Sandstone, rocks of Palaeozoic age that were moulded, like the rest of Wales, during the late Tertiary period when they were thrust skyward to form hills and mountains. Glacial erosion during the Pleistocene ice ages greatly modified their contours, along with wind, rain and snow in more recent times. Outcrops of Millstone Grit and Carboniferous Limestone add to the geological mix. The area also forms part of the Fforest Fawr Geopark, the first of its kind in Wales, set up to promote the wealth of natural and cultural interest in the area. Here, as elsewhere in Wales, there is a high degree of correlation between rocks and relief.