succession includes a sequence with a thickness of more than 1800 m in the west. The Coal Measures were laid down on a low-lying waterlogged plain with peat mires immediately south of an ancient geological feature known as the Wales-London-Brabant High. Variscan Orogeny From late Carboniferous times, through the Permian, South Wales lay on the northern margin of the Variscan orogen, an area affected by a complex continental collision taking place to the south. The most intensely affected rocks are those of south and central Pembrokeshire where steeply dipping and vertical strata are commonplace and multiple folding, faulting and overthrusting are well seen in coastal sections. Southern Carmarthenshire and the western part of the South Wales Coalfield were affected to a lesser extent. Old Caledonoid weaknesses such as the Neath Disturbance were reactivated at this time. Permian Rocks dating from the Permian period occur in North Wales underlying the Vale of Clwyd and extend into the northeastern fringes of the country from the larger bodies of such rock in Cheshire and Shropshire. The Permo-Triassic rocks in the northeast of Wales are largely concealed by recent material deposited by rivers and the Devensian icesheet. Thicker sequences of Permo-Triassic rock are known to underlie the Bristol Channel, Cardigan Bay and the Irish Sea off the North Wales coast. Mesozoic Triassic Triassic sandstones form much of the coast between Barry and Penarth and extend eastwards along the Monmouthshire coast to the English border at Chepstow. They also occur more sporadically further west between Ogmore-by-Sea and Kenfig. There are very localized occurrences of Triassic material in Gower and south Pembrokeshire, much of it breccia-fill of fissures in underlying Carboniferous Limestone. Triassic sandstones are also found along the border with Cheshire and Shropshire, though most often concealed beneath recent fluvial and glacially derived material. Jurassic Rocks dating from the Jurassic period occur widely across the Vale of Glamorgan. Much of the Glamorgan coast between Ogmore-by-Sea and Barry is formed by cliffs of layered Jurassic limestone known as the Lias. Extensive and spectacular shore platforms have been developed e.g. near Southerndown, as these cliffs have retreated inland through frequent rockfall. Cretaceous There are no rocks of Cretaceous age in Wales but they are known to be present within the sub-sea basins off the Welsh coast e.g. Celtic Sea and the Bristol Channel. Cenozoic Palaeogene and Neogene There is scant evidence for rocks of the Palaeogene and