CYMRAEG search COVID-19 (Coronavirus) For details on service changes visit our Coronavirus information and advice page. GEOLOGY Home / About the National Park / Geology SHARE THIS When you think about the Pembrokeshire Coast National Park you may conjure up images of beautiful beaches, panoramic views from the Coast Path and quaint fishing villages complete with cosy local pubs. You won’t necessarily be thinking about what the cliffs are made of or what’s beneath your feet. However, believe it or not, the very stones that make up the foundations of the Park are in fact one of the main reasons we were designated as a National Park in the first place. The Pembrokeshire Coast National Park displays an extraordinary variety of rock types and landforms. It is this geodiversity that was one of the deciding factors leading to the designation of the Pembrokeshire Coast as a National Park in 1952. The 186-mile Pembrokeshire Coast Path National Trail was established soon afterwards. The National Trust has also purchased many stretches of the coastline to protect it for future generations. This shows exactly how precious, and indeed vulnerable, our geological heritage is. The diversity of rocks and the quality and extent of the exposure has attracted the attention of geologists for many centuries. This resource is considered so significant for research and education that around 40% of the coastline includes geological features that are protected by Sites of Special Scientific Interest (SSSI). Most of these SSSI also have biological features. The ages of the rocks range from late Precambrian to late Carboniferous (c.650-290 million years old). Rocks and unconsolidated deposits of Quaternary age are also widely distributed, usually seen overlying the older rocks. READING THE ROCKS The Precambrian rocks are exclusively igneous, mostly volcanic ashes and fairly large intrusions of microgranite and diorite. They are exposed on the south western tip of the St David’s Peninsula and on the north and south facing cliffs of the innermost part of St Brides Bay. The Cambrian rocks are mostly sedimentary, a basal conglomerate overlain mainly by sandstones but some mudstones occur in the middle part of the sequence. They are exposed along the southern and western sides of the St David’s Peninsula and in a less frequently visited section of coastline between Abercastle and Abermawr. Apart from this, the northern coastline of Pembrokeshire, from Ramsey Island to just east of Fishguard, is composed entirely of Ordovician rocks, mainly slates and volcanic rocks but from Dinas Island to the Teifi Estuary the cliffs mostly display turbidite sequences (interbedded sandstones and mudstones). Silurian rocks, both volcanic and sedimentary, form Marloes Penisula and Skomer Island. OUR GEOLOGY ROCKS! In South Pembrokeshire the outcrops of different rocks extend WNW-ESE and are repeated by the effects of folding and erosion as shown on the map. All these distinctive rock types are also present in other areas of South Wales and will be familiar to many people. The Old Red Sandstone consists of bright red mudstones, siltstones and sandstones, together with some conglomerates and green sandstones. The Carboniferous Limestone is usually light grey on weathered surfaces, although often darker on fresh surfaces. Thickness of beds is variable and limestones may be interbedded with darker calcareous mudstones. The Millstone Grit and Coal Measure sequences are similar in character, consisting of dark grey or black shales and light grey sandstones (the latter are often orange-brown on weathered surfaces). The Millstone Grit has a basal and upper gritty sandstone sequence, separated by rocks of more variable character. The Coal Measures include thin coal seams (locally referred to as veins) of anthracite grade. Quaternary deposits, usually mantling the top of cliffs but occasionally forming the entire cliff like at Druidston Haven and Abermawr include till (‘boulder clay’), solifluction flow deposits (stony clays in which tabular clasts show a preferred alignment), frost-shattered scree and wind-blown sand (the latter two types usually naturally cemented) and loess. LANDFORMS TO LOOKOUT FOR Small remnants of wave-cut platforms sometimes with cemented pebbles and shells, formed c.125,000 years ago when sea level was c.5 metres higher than at present, are found at many locations, notably Poppit Sands, Porth Clais, Marloes Sands, Freshwater West and Broad Haven. Sand dune systems are found at a number of locations. Landforms include all the typical ones formed by coastal processes (including many text book examples), but remnants of older scenery may also be present, including partially drowned meltwater channels such as Solva Harbour, reworked karst features (eg. caves and blow-holes of the limestone cliffs), and valley slope remnants (represented by coastal slopes with modern sea cliffs below). Evidence of landsliding and rockfall are very common and careful visual assessments of cliff stability should be made before commencing any climb. READ MORE ABOUT THE NATIONAL PARK'S GEOGRAPHY MORE ABOUT THE NATIONAL PARKS' GEOLOGY VOLCANIC HISTORY You will often hear it said that isolated craggy hills like Carn Llidi and Penbiri near Whitesands Bay or Garn Fawr on Strumble Peninsula are the erod... READ MORE ON VOLCANIC HISTORY GEOLOGICAL LANDSCAPE Pembrokeshire’s landscape is forever being photographed and painted, appreciated by the walker and artist alike. But what has created this landscape... READ MORE ON GEOLOGICAL LANDSCAPE GEOLOGICAL CONSERVATION Forget castles, Iron Age hill forts, golden sandy beaches and the ice cream van. We’re talking about what’s under your feet! The very stones on wh... READ MORE ON GEOLOGICAL CONSERVATION CLIMATE CHANGE What do us Brits like discussing more than anything else?! The weather of course! From tropical landscapes to glaciers and ice sheets, Britain has bee... READ MORE ON CLIMATE CHANGE GET IN TOUCH Contact us and register your details to get the latest updates on what's happening in the Pembrokeshire Coast National Park. CONTACT US National Park Office Llanion Park Pembroke Dock Pembrokeshire, SA72 6DY Tel: 01646 624800 Email: info@pembrokeshirecoast.org.uk VISITING Plan your visit Access for All Carew Castle and Tidal Mill Castell Henllys Iron Age Village Oriel y Parc Gallery and Visitor Centre QUICK LINKS About the National Park Authority About the National Park Planning Contact Us News Jobs Accessibility Statement Privacy Policy Terms & Conditions Cookie Policy Sitemap © 2021 Pembrokeshire Coast National Park. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies. However you may visit Cookie Settings to provide a controlled consent. Cookie settingsACCEPT