Discover Wales and Explore its Geodiversity and Fossils of Green Bridge and Elegug Stacks
- Wayne Munday
- May 2
- 4 min read
Sip back and discover Wales and explore the Green Bridge and Elegug Stacks of the Pembrokeshire Coast National Park. The Pembrokeshire Coast has one of the United Kingdom's smallest National Parks offering a remarkable landscape primarily designated for its coastal features and international ecological importance in supporting a several rare species. Stretching nearly all of Pembrokeshire’s 420 Km coastline including all offshore islands, the Daugleddau estuary, the Preseli Hills, and Gwaun Valley the Pembrokeshire Coast National Park covers over 615 Km2. The best way to explore and experience the park is to walk along the Pembrokeshire Coast Path National Trail a 299 Km trail that forms one of eight parts of the larger 1,400 Km Wales Coast Path. The northern segment of the path features craggy volcanic outcrops while the southern portion presents towering Carboniferous Limestone cliffs that include the Green Bridge and Elegug Stacks.
The Pembrokeshire Coast National Park maybe small but it has considerable geological complexity and a record that spans from the Late Precambrian to the Late Carboniferous periods between 650 - 290 million years ago. The rocks range from volcanic ashes and large intrusions of microgranite and diorite to sedimentary Devonian Old Red Sandstone, Namurian Millstone Grit, Coal Seams and Carboniferous Limestone.
The older rocks and landforms of Pembrokeshire and much of Wales is covered by Quaternary deposits of boulder clay, solifluction deposits, scree, loess, and wind-blown sand from the last 2.6 million years from the impact and influence of climate change by a sequence of ice ages and warmer interglacial periods.
The Green Bridge (Welsh language: Pont Werdd Cymru) and the Elegug Stacks are striking Carboniferous Limestone coastal formations sculpted by the destructive erosion by waves by the forces of hydraulic action, compression, abrasion and attrition that continuously exploit the weaknesses in the limestone's faults and folds.
These faults and folds are no more dramatic than the striking coastal chasm seen at Huntsman's Leap. This narrow, steep-sided cleft was eroded by the sea over millions of years. The verticality and narrowness is due to the alignment of natural jointing within the limestone.
These rocks would have been folded and faulted during the Variscan Orogeny a mountain-building event that occurred between 370 - 290 million years ago in the Late Paleozoic. This orogeny resulted from the collision of the continents Laurasia and Gondwana leading to the formation of the supercontinent Pangaea.
The Green Bridge is a natural arch at over 24 meters high and spanning over 20 meters wide was formed when waves eroded caves on either side of a headland until they eventually merged. The Elegug Stacks are also known as Stack Rocks and are the remnants of a collapsed Carboniferous Limestone arch. Now standing as isolated pillars of rock they are detached from the mainland. Located just west of Flimston Bay these formations are not only remarkable geological landmarks they are also safe havens for nesting seabirds such as guillemots, razorbills, and fulmars. The name "Elegug" is Welsh for "guillemot".
The sedimentary rocks of Pembrokeshire including the Carboniferous Limestone was formed while Britain was part of the Gondwana supercontinent. These rocks tell a story of a time when Britain was moving northwards by tectonic activity through tropical and sub-tropical zones. During the Carboniferous Period, Britain was situated near the Equator and global sea levels transgressed submerging the land.
These limestone exposures are part of the broader Carboniferous Limestone Supergroup formed during the Early Carboniferous period. This is a major geological unit comprising of limestones, mudstones, and some sandstones formed during the Dinantian Epoch of the Carboniferous Period between 363 - 325 million years ago and is widespread across Great Britain and Ireland with prominence in North Wales, the Peak District, Yorkshire Dales and parts of Cumbria, Bristol and the Mendip Hills of Somerset.
The Carboniferous Limestone of Pembrokeshire is visibly exposed from Tenby to Frainslake Sands along the cliffs at St Govan’s Head, Stackpole Head, Lydstep Point, Huntsman’s Leap as well as Green Bridge and Elegug Stacks.
The Pembroke Limestone Group has marine fossils of corals, brachiopods, crinoids, bryozoans, and molluscs. Several locations across Pembrokeshire are known for fossils including West Angle Bay for crinoids, Freshwater East and Stocker Hole have fossil-bearing pebbles containing corals, brachiopods and crinoid fragments and Lydstep Point has corals, crinoids, gastropods and brachiopods.
Interestingly, Pembroke Castle was constructed from local Carboniferous Limestone. Originally built in 1093 by Norman knight Roger of Montgomery as a timber fortification in 1201 and under the direction of William Marshall the Earl of Pembroke the castle underwent a major transformation into a formidable limestone fortress. Apparently, crinoids, corals, and brachiopods can be seen on the weathered walls of Pembroke Castle.
Please note that removing fossils from the Pembrokeshire Coast National Park or any area designated an SSSI requires prior permission from the landowner. Collecting specimens is generally discouraged and photographing them is much more preferred.
