Rock Textures at Eype 1

View of the cliff on the western shore at Eype showing stratification

View of the cliff on the western shore at Eype showing stratification

The interesting thing about Eype Beach is that you don’t have to climb the cliffs to see the rocks in detail – the rocks come to you! Boulders of sandstone and limestone from high in the cliffs regularly collapse to the beach, which becomes strewn with them, and affords an opportunity to examine the composition of, and the fossil content of, the variety of rock types represented in the strata above shore level. Even the low, thick band of softer mudstones and shales slips down on a fairly regular basis, and liquified by small streams, oozes over the shingle of the upper beach.

It’s going to take me a while to work out which rock is which. However, I can say that Eype Beach has two different geologies more or less separated at Eypesmouth where a small stream cuts its way down a steep-sided valley through the predominantly soft rocks. If you turn right and westwards where the stream breaks through to the shore, and walk towards Thorncombe Beacon as I did, then on your right-hand side are cliffs made up of several virtually horizontal rock strata of different types of sedimentary rock. The lowermost layer, nearest to the level of the shingle beach, is a 55 foot depth of blue-grey Eype Clay Member made up from micaceous silty mudstone and shale – also called  the Micaceous Beds – from the Middle Jurassic Period.

Above the blue-grey mudstone, are the yellow layers of silts and sandstones of the Down Cliff Sand Member and the Thorncombe Sand Member – with sporadic fossil beds, and thinner bands of calcareous sandstone and ironshot limestone. You can easily see the contrasting colours of the different rocks in the cliff face.

I had hoped to find some brittle star fossils, that was the main aim of the visit, but I wasn’t lucky on this occasion. It was rather hot on the day and I don’t think I walked far enough along the shore to be in the most likely location. The Starfish Bed with Palaeosoma egertoni is at the very base of the Down Cliff Sand Member which itself overlies the Eype Clay Member. Large blocks of this rock fall to the beach – but you have to hope that the block has fallen the right way up for you to see the brittle star fossils, and also hope that a professional fossil hunter has not got there before you! I’ll have to keep on keep searching.

View looking west toward Thorncombe Beacon from the base of the cliff at Eype

View looking west toward Thorncombe Beacon from the base of the cliff at Eype

It was clear that many types of rock were identifiable on the beach; even the modern mud-slicks and clay seepages were interesting because they demonstrate and replicate the same  processes that would have contributed to the textures and patterns of the ancient rocks. As the soft muds dried out in the sun, the surfaces were beginning to form a crazy paving patchwork of cracks – the same as could be observed in nearby slabs of rock. As the liquified clays dribbled outward from the base of the cliff rock exposure, they incorporated assemblages of small pea-sized pebbles and who-knows-what man-made objects that might end up in rock strata of the future.

So the gallery of pictures today just shows details of a small selection of the rocks and sediments to be found on Eype Beach with a range of the natural textures and patterns they exhibit. It’s the starting point for the Eype geological learning journey.

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Sweyne’s Howse

 

In the earlier  discussion about the strange stone that might be an ancient axe – which was found on the Worm’s Head Causeway on the Gower  Peninsula – I mentioned the nearby Neolithic chambered tombs. The most frequently found ancient tools in this area are the polished stone axes from the Neolithic. There are some earlier tools – but these are flint, and were probably made on a flint-working site that existed on the tidal island of Burry Holms at the north end of Rhossili beach. (The Worm’s Head Causeway is at the southern end of Rhossili beach).

The Neolithic period started about 6,000 years ago and was marked by an influx of farming communities who cleared the land for grazing and cultivation. These people left tools behind them, the ones most frequently found being the polished stone axes that have been recovered from sites such as Paviland, Oystermouth and Barland. The most noticeable remains of these people are the large megalithic structures. On Rhossili Down are the remains of chambered tombs belonging to this category: the best known of which are Sweyne’s Howses (there are two of them).

The images in this post show the location of Sweyne’s Howse on Rhossili Down – positioned on the land the Neolithic settlers cleared, at the junction between freely-drained and poorly drained soils, recognisable by the heathland vegetation on the one hand and the fertile cultivated fields on the other. The upland is covered with vibrant pink flowering Ling and Heather in the summer, and the ground is still grazed by sheep, cattle, and roaming wild ponies.

The tomb is now located amongst cleared bracken on the lower slopes of the Down. It looks very different from various angles, being comprised of massive slabs of local Old Red Sandstone Conglomerate – slabs that look like pillars when viewed end-on. The rocks are covered with a thick layer of lichens.

From higher up on Rhossili Down, it is possible to look down towards the north-west and see the island of Burry Holms where there was an earlier Mesolithic flint-working site. Looking down to the south-west, you can see the Worm’s Head and its Causeway where the strange stone was found.

I now have an appointment to take the stone to an archaeologist who is a specialist in stone tools at the National Museum of Wales; and a geologist will also be on hand to give their opinion. I am hoping that the stone is an axe – but I am also prepared to be disappointed because I know how easy it is for an amateur like myself to be mistaken about this kind of thing.

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A Curious Beach Stone

A stone found on the Worm's Head Causeway

I’m always looking at pebbles and beach stones but I wasn’t the one who first spotted this curiously shaped stone. My companion picked it up from where it lay in a shallow tide pool out on the Worm’s Head Causeway, which is at the end of the Gower Peninsula. It is a fairly symmetrical and flattened leaf-shape; and measures approximately 12 by 7 cm. It seems to be made of limestone – but I could be wrong about that.

One edge is smooth and rounded. The other is thinner and sharper. Overall, it is well worn and smoothed – it has been rolling around on the shore for a considerable time. The surface has evidence of both infesting and encrusting organisms. There are small burrows made by marine worms and also by sponges – I’m not sure what types they are. At the broad end is a larger hole that perforates the stone. It looks a lot like part of a tunnel that might have been bored by a bivalved mollusc such as a Flask Shell or a Wrinkled Rock Borer. Within the hole, small acorn barnacles have attached their plates. Over the flat surfaces of the stone are minute lace-like Sea Mats and the occasional calcareous tube made by a worm. The whole stone feels balanced and comfortable in the hand.

I’m quite excited about this stone because I think it might be an ancient hand axe! I’m going to send these pictures to experts at the National Museum of Wales for their opinion. Maybe you, the reader, knows something about this object and can tell me something about it. I have read that a really old Neanderthal flint axe was once found at Rhossili; and Palaeolithic stone axes have been recovered from some of the local caves. However, most of the axe heads discovered in this area have been Neolithic; and physical evidence for Neolithic occupation of the locality can still be easily seen in the megalithic chambered tombs – like Sweyne’s Howes on Rhossili Down.

If this piece of rock is not just an oddly shaped beach stone, and it is in fact an axe head, then its most curious feature of all must be the perforation. From a naturalist’s point of view, it seems most unlikely that a rock boring mollusc would have burrowed into such a thin section of rock as presented by a lost hand axe. That being so, it raises the possibility that the rock was chosen for making into a hand axe because it already had the hole in it. Microscopic examination of the inner surface of the hole, beneath the encrusting barnacles, could reveal whether the hole is naturally made by some organism or if it is man-made. Surely a most unusual phenomenon in ancient axe-making.

I’ll keep you posted about developments. Fingers crossed that it really is something special – but maybe it is only in my imagination.

Flat surface of a stone found on the Worm's Head Causeway

Flat surface of a stone found on the Worm's Head Causeway

Possible worked sharp edge to the strange beach stone

Possible worked sharp edge to the strange beach stone

Blunt, rounded edge to the odd beach stone

…….and where the stone was found:

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More about Joggins Fossil Cliffs

View of Joggins Fossil Cliffs inclined strata

As you walk northwards along the shore at Joggins Fossil Cliffs, you are walking backwards through time. As you look straight-on at the inclined rock strata exposed in the cliff face, the strata are rather like the pages of an open book, with the beginning of the story (or the chapter might be a better simile) told by the pages furthest to the left; and the the end of the chapter to the right. Each layer of rock has a different thickness and composition. Each stratum represents a different event or episode in geological history. Altogether, the Joggins Fossil Cliffs site comprises a 14.7 km coastal section with the majority of detailed stratigraphical and sedimentological studies being concentrated in about a 4 km section of the Joggins Formation.

Originally, the layers of rock were laid down in horizontal beds but, over time, earth movements have tipped them up so that now these are all lying at an angle of about 20 degrees. The conditions under which these sedimentary rock layers were laid down changed in a cyclical way. The location in which the sediments were formed was basically a coastal environment.  Periodically the sea moved in and out. This meant that the place became either drier or wetter, more marine, more freshwater, or more terrestrial depending on the prevailing sea level.

When the sea level was high, the area was covered in shallow sea. This is when the limestone rocks were formed. When the sea level fell, the area become more terrestrial. The sea level changed according to such major phenomena as the movement of tectonic plates in the earth’s crust or due to eustatic land/sea level changes linked to the build-up or the thawing of ice sheets. The terrestrial environments were not always absolutely dry but were muddy swamp-like places with stands of vegetation including large tree-like plants.

The coastal strip was traversed by rivers that cut channels in the sediments and brought down large quantities of sand and other materials that could bury the coastal plants in times of flooding. This is where the sediments that formed the sandstone layers came from. In-filled river channels are preserved in the cliff face and are also visible at low tide as long lines of rock projecting from the surface of the shore as they extend out to sea. Mudstones and shales were also formed. Rapidly buried rotting vegetation and trees were sometimes converted under pressure to coal.

The rocks at Joggins belong to the Cumberland Group of the Langsettian in the Upper Carboniferous Pennsylvanian period. The rocks along the total 14.7 km stretch of cliffs are made up of four formations: from The Ragged Reef Formation,  (the youngest to the south), then the Springfield Mines Formation, next the Joggins Formation itself, and then to the Little River Formation and Boss point Formation in the north. I was only able to walk from Dennis Point (SMF) to Coal Mine or Hardscrabble Point (JF) because of the state of tides and weather.

On my visit I found it impossible to work out which strata were which. However, since returning home and doing a bit of research, I have discovered that a sedimentological log has been recorded for the length of the Joggins Formation by Davies et al 2005. Each stratum was measured to the nearest centimetre and its composition, structure, and associated fossils described. This means that when I visit again, I will be well equipped to ‘label’ each stratum that I photograph – with a little help from the published diagrams, and hopefully an expert guide from the Joggins Fossil Cliffs Visitor Centre.

It has been possible to find out what some of the rock patterns, structures and textures represented. For example, there were many examples of preserved wave and current ripples patterns on beach stones and boulders as well as in bedrock layers:

Ironstone or siderite nodules formed of iron carbonate by precipitation in evaporating shallow water; and clay galls derived from dried mud polygons incorporated into sandstones are common.

Cross-bedding of sedimentary layers made by deposition from migrating streams and rivers; patterns of cracks in sun-baked muds; and conglomerates  of various sorts with small pebbles and rock fragments brought down by running water and cemented into a matrix, were also seen.

Wrapped up within these layers of sedimentary rock are numerous, sometimes spectacular fossils, preserved in situ where they lived and died. The plant fossils include huge ‘tree’ trunks still rooted in their life position; fossil stems, roots, leaves, and diverse carbonised items of vegetational debris abound. Invertebrate fossils such as bivalved and gastropod molluscs are also found, as are pieces of giant millipede, dragonflies and whip spiders. Trace fossils of tracks left by Arthropleura millipedes and reptiles occur. In fact, the actual skeletons of small reptiles, such as Hylonomus lyelli – one of the first reptiles to evolve on earth, have been recovered from hollow tree trunks at this site. More about the fossils in the next post.

REFERENCES

Calder, John (2012) The Joggins Fossil Cliffs: Coal Age Galapagos, Province of Nova Scotia, Department of Natural Resources, Crown Copyright, ISBN 978-1-55457-473-5.

Davies, S. J., Gibling, M. R., Rygel M. C., Calder, J. H., and Skilliter D. M. (2005) The Pennsylvanian Joggins Formation of Nova Scotia: sedimentological log and stratigraphic framework of the historic fossil cliffs, Atlantic Geology, 41, pp 115 – 142.

Joggins Fossil Institute, The Joggins Fossil Cliffs Field Guide.

Nova Scotia Department of Natural Resources, Nova Scotia Geological Highway Map.

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Rock Patterns & Textures at Joggins – Part 2

 

Cliff face rock strataMore patterns and textures of rocks at Joggins Fossil Cliffs in Canada. You might ask what is the significance of these images? The truth is that they not only seem to me to be examples of natural abstract geological art but they also represent some of the many the rock types at this location – rocks that are providing geologists, palaeontologists and palaeo-environmentalists with vital information about the way the world was in the late Carboniferous Period.

Important discoveries were first made at this site in the mid 1800’s and have been continuing since then – but there has been an upsurge in research into these rocks in recent years. I can do no better than to quote from the abstract of the paper by Grey & Finkel (2011) that summarises the situation:

The Joggins Fossil Cliffs UNESCO World Heritage Site is a carboniferous coastal section along the shores of the Cumberland basin, an extension of Chignecto bay, itself an arm of the bay of Fundy, with excellent preservation of biota preserved in their environmental context. The Cliffs provide insight into the Late carboniferous (Pennsylvanian) world, the most important interval in Earth’s past for the formation of coal. The site has had a long history of scientific research and, while there have been well over 100 publications in over 150 years of research at the Cliffs, discoveries continue and critical questions remain. Recent research (post-1950) falls under one of three categories: general geology; paleobiology; and paleoenvironmental reconstruction, and provides a context for future work at the site. While recent research has made large strides in our understanding of the Late Carboniferous, many questions remain to be studied and resolved, and interest in addressing these issues is clearly not waning.

REFERENCES

Grey, Melissa & Finkel, Zoe E. (2011)  The Joggins Fossil Cliffs UNESCO World Heritage site: a review of recent research, Atlantic Geology, 47, pp 185 -200.

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Rock Patterns & Textures at Joggins – Part 1

View looking south at Joggins Fossil CliffsJoggins Fossil Cliffs are a UNESCO World Heritage Site on the Nova Scotia shore of the Bay of Fundy on the Atlantic coast of Canada. The stratified rocks in the cliffs were laid down in the Upper Carboniferous (Pennsylvanian) Period between 310 and 300 million years ago. They consist of alternating layers of sandstone, siltstone and shale, including coal measures. They are similar, though not identical, in composition, formation, and date to the wonderful Cliffs of Moher on the Atlantic coast of Ireland.

Joggins Fossil Cliffs are particularly famous for their plant fossils, with large fossilised tree stumps weathering out of the cliffs every year. Fossils of small amphibians, and some of the first reptiles that ever lived, have also been recovered from inside tree stumps. These fossils were first discovered in the mid 19th century by the English palaeontologist Sir Charles Lyell (who was a friend and colleague of Sir Charles Darwin), and the Canadian Sir William Dawson.

View looking north at Joggins Fossil CliffsI will in due course, in following posts, develop the themes of the geology of this location, the fossils it contains, and the way it has been mined for coal. For the moment, however, I am posting images of some more abstract details of the natural fracture patterns and textures in these spectacular cliffs.

REFERENCES

Ferguson, Laing (1988) The Fossil Cliffs at Joggins, Nova Scotia Museum, Halifax, Nova Scotia, ISBN 978-1-55109-669-8.

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Pictures from an Isle of Portland walk – Part 5

 

The rocks and soils above and below the raised beaches at the southern tip of the Isle of Portland in Dorset, England, exhibit features that are believed to be associated with freeze-thaw  periglacial conditions. These photographs show interesting rock features in the Upper Jurassic limestone that I think may possibly relate to the cold period prevailing prior to the interglacial period in which the younger of the two raised beaches known as Portland East Beach (as shown in the previous post) were formed.  Pugh & Shearman (1967) first described these cryoturbation features on the Isle of Portland, and later  (Goudie & Brunsden, 1997) stated that:

At the base of the raised beach gravels, the shore platform is heaved, cracked, and warped to a depth of up to 3m.  The meticulous observer will also be able to reconstruct crude polygons of angular boulders which stand on edge. Such features are thought to be caused by frost action under cold conditions and are commonly known as periglacial (tundra) patterned ground and, more specifically as rock blisters.

REFERENCES

Goudie, A. and Brunsden, D. (1997) Classic Landforms of the East Dorset Coast, Series Editors Rodney Castleden and Christopher Green, The Geographical Association, ISBN 1 899085 28 9.

Pugh, M. E. and Shearman, D. J. (1967) Cryoturbation structures at the south end of the Isle of Portland in Proceedings of the Geologists’ Association, 78, pp 463 – 471.

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Pictures from an Isle of Portland Walk – Part 4

On the southern tip of the Isle of Portland, in Dorset, England, raised beach deposits provide evidence of higher sea levels at some periods during the Quaternary. There are two separate raised beaches, the more publicised Portland West Beach just to the west of Portland Bill Lighthouse – and another 200 metre long section of Portland East Beach to the east of the lighthouse and behind the Lobster Pot Café.

The Portland East Beach raised beach deposits are shown in these photographs. They sit on top of layers of limestone and are made up of pebbles, larger beach stones, and boulders of Portland and Purbeck limestone, flint and chert – intermixed with seashells. The shells in the images here are all marine gastropod shells of the common periwinkle. All the beach material is bound together in a cement-like matrix of high calcium content, the whole being frequently stained rusty by iron from percolating water. It is interesting to note how many of these ancient beach stones were already riddled with small holes and burrows made by sea creatures, such as Polydora-type worms and boring bivalve molluscs like piddocks, before being isolated and consolidated into the solid layer of beach deposits when the sea levels went down. If you look closely, you can actually see the piddock shells retained within the bore holes of some of the stones..

The whole raised beach layer is up to 0.45 metres thick but is mostly patchy in its distribution. Amino-acid analysis of the mollusc shells suggests that they date from the Ipswichian period of 125,000 years before present, which was the last interglacial. The sea level at that time would have been about 6.95 – 10.75 metres above present sea level. The Portland East Beach is a more recent deposit than the Portland West Beach that has been dated by the same method to 210,000 BP, at which time the shoreline would have been about 14.5 metres above present levels. The higher sea levels are thought to have resulted from the melting of the ice caps in these warmer interludes in the Ice Age, and it is also possible that some local tectonic uplift of the land mass may have played a part.

REFERENCES

Barton, C. M.; Woods, M. A.; Bristow, C. R.; Newell, A. J.; Westhead, R. K.; Evans, D. J.; Kirby, G. A.; Warrington, G. (2011) Geology of south Dorset and south-east Devon and its World Heritage Coast, Special Memoir for 1:50 000 geological sheets 328 Dorchester, 341/342 west Fleet and Weymouth and 342/343 Swanage, and parts of sheets 326/340 Sidmouth, 327 Bridport, 329 Bournemouth and 339 Newton Abbot, Compiled by M. A. Woods, British Geological Survey, Keyworth, Nottingham.

Davis, K. H. and Keen, D. H. (1985) The age of Pleistocene marine deposits at Portland, Dorset, Proceedings of the Geologists’ Association, 96, pp 217 – 225.

Goudie, A. and Brunsden, D. (1997) Classic Landforms of the East Dorset Coast, Series Editors Rodney Castleden and Christopher Green, The Geographical Association, ISBN 1 899085 28 9.

Keen, D. H. (1995) Raised beaches and sea levels in the English Channel in the Middle and late Pleistocene: problems of interpretation and implications for the isolation of the British Isles, in Island Britain: a Quaternary perspective, Preece, R. C. (editor). Geological Society of London Special Publication, No. 96, pp63 – 74.

Keen, D. H. (1985) Late Pleistocene deposits and mollusca from Portland, Dorset, Geological Magazine, 122, pp 181 – 186.

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The Cliffs of Moher Strata

Rock strata at the Cliffs of Moher

The Cliffs of Moher rise to 214 metres above the sea and stretch for 8 kilometres along the west coast of Ireland in County Clare. They are spectacular. This impressive site has formed the backdrop for box-office hits like the ‘Princess Bride’ and ‘Harry Potter and the Half-Blood Prince’. The first landfall west of the cliffs is the Atlantic coast of Canada – 3000 kilometres away. You can get an idea of the vast scale of the cliffs by noting the minute figures of the people walking along the cliff-top footpath and rocks in the photographs below.

The Cliffs of Moher take their name from a ruined promontory fort known as “Mothar” that once stood at the southern Hag’s Head end of the cliffs but which was pulled down in Napoleonic times to make way for a signal tower.

The Cliffs are part of the famous Burren landscape. However, they are composed of relatively more recent Upper Carboniferous Namurian Period rocks – the Central Clare Group and Gull Island Formation, that overlie the Clare Shale Formation. These sandstones, siltstones, mudstones, and shales were all deposited on top of the more familiar Carboniferous Visean limestones of the perhaps better known eroded scenery of the Burren. The sediments of which the cliff rocks are made, were originally brought down by a large river to a huge delta system that was subsequently consolidated into rock about 300 million years ago. The Burren and the Cliffs of Moher are a recognised UNESCO Global Geopark.

Over long periods of time, some places at the base of the cliffs have been worn away by wave action to form sea caves. In fact, Ireland’s largest surfing wave (called Aileen’s) is at the base of these cliffs. Continued eating-back of the rock where these caves have been scooped out of the cliff, can lead to the formation of sea arches through which the tides can freely flow. When the arches themselves eventually collapse, isolated pillars of rock named as sea stacks are created. The final stage of erosion by the sea causes the stacks to be worn down to ever-decreasing stumps of rock. These caves, sea stacks and stumps can be seen from the cliff-top pathways.

The strata in the cliffs are almost horizontally bedded and the ledges which jut out from the cliff face, where the alternating hard and soft rock layers have been differentially weathered, form ideal nesting sites for thousands of puffins, guillemots, razorbills, fulmars, kittiwakes, peregrine falcons, and choughs. Wild flowers abound on the cliffs in the summer months. The great height of the cliffs provides an ideal viewpoint to look for dolphins and seals in the water below – and maybe even the occasional basking shark, humpback or Minke whale.

The best vantage point of all is the top of O’Brien’s Tower perched near the cliff edge. It was purpose built in the 1835 for tourists who, even then, were flocking to marvel at the cliffs. Up to a million visitors a year now come to the Cliffs of Moher and, even on a cold March day early this year when I was there, people were arriving by the coach-load to enjoy the wonder of the cliffs and to learn about their significance in the fascinating and extremely well-presented Cliffs Exhibition. Although most visitors walk no further than O’Brien’s Tower, this is enough to give them a real sense of awe at this incredible geological site.

O'Brien's Tower at the Cliffs of Moher

REFERENCES

Cliffs of Moher Visitor Experience, Co. Clare – Visitor guide leaflet.

Sleeman, A. G., Scanlon, R. P., Pracht, M. & Caloca, S. (2008) Landscape and Rocks of the Burren: A special Sheet in the Bedrock Geology 1:50,000 Map Series, published by Geological Survey Ireland, ISBN 189970257-1.

Hennessey, R., McNamara, M., and Hoctor, Z. (Compilers) (2010) Stone, Water and Ice – A geology trip through the Burren, The Burren Connect Project, ISBN 0-9567204-2-9.

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A few fossils at Mewslade Bay

Coral fossil in Carboniferous Limestone

In the way that some people have their own personal trainer or financial adviser, what I really need is my own personal geologist! I am learning by looking, consulting geology maps, reading books, consulting academic treatises, and visiting museums but translating all the information into an interpretation and understanding of the rocks and fossils that I see on the shorelines, is a difficult task and I know it is open to error. Particularly since the way the strata are categorised and named has changed over time.

 In 1970 when the 3rd edition of the British Regional Geology Series for South Wales was published, the stratigraphical succession of the Carboniferous comprised the Cleistopora Zone (K), Zaphrentis Zone (Z), Lower Caninia Zone (C1), Upper Caninia Zone (C2S1), Seminula Zone (S2) and Dibunophyllum Zone (D). These zones have been reclassified and renamed so that in the current version of the British Regional Geology Series for Wales (2007) the Carboniferous is divided up into the Avon Group, Black Rock Limestone Group, Gully Oolite Formation, Caswell Bay Mudstone Formation, High Tor Limestone, Hunts Bay Oolite Formation, Oxwich Head Limestone Formation and Oystermouth Formation. Cross-referencing the information from old and new sources is not always straightforward.

I am enjoying what I do, and learning a lot as I go along, with the posts I write being part of the learning process. However, it would be really great one day to go out in the field with a professional geologist, who has consummate knowledge of the areas I study, to see the rocks and fossils from an expert perspective to confirm my identifications and ideas.

With all that in mind, I have been closely examining the rocks that have been recently exposed by the removal of overlying sand at Mewslade Bay in Gower – before they disappear from view again – the sand is rapidly returning after the extraordinary winter clear-out of all loose sediments. The temporary exposure of the hidden rock surfaces, in combination with an elemental scouring that has virtually scrubbed the rocks clean of encrusting organisms, and has revealed a number of fossils that I had never noticed before.

These fossils seem to be mostly gastropod molluscs and corals with a few bivalves or brachiopods. They are not the perfect fossils that you see on display in museums; and you cannot pick them up and take them home in your pocket. They are generally small and are embedded in the rocks; and what you see at the surface is a part of the fossil from all sorts of odd angles, so they are not always easy to recognise for what they are. They all seem to have had the original hard parts replaced by crystalline calcite which is normally white but often here tinted pink or red. The colour is mostly likely to be caused by staining from iron. There are also numerous, seemingly random, streaks of calcite in the rocks, some of them extending outwards from the fossils or traversing them.

Putting a specific name to the different types of fossils is somewhat dependent on knowing the type of rock in which they are embedded. Usually, somewhere, there is an academic work listing all the fossils that are found in a particular rock type. But here it gets complicated. I know that the rocks on this part of the Gower Peninsula are Carboniferous Limestone. However, the Carboniferous Limestone is composed of many named strata or layers laid down at different times according to the varying conditions prevailing. The Carboniferous Period started 359.2 +  2.5 million years ago; and ended 299 + 0.8 mya. The Carboniferous has two stages, and the earlier Dinantian stage (to which these Mewslade rocks belong) finished 318 mya.

The rocks were laid down in a warm tropical sea subject to rises and falls in sea level, that periodically resulted in exposure of the surface rocks to aerial weathering and increased input of  terrestrial materials. The fossils are the remains of the animals that were living, dying and being buried in the seabed sediments of that tropical sea. The subsequently uplifted rock strata have been affected by earth movements that have caused tilting, fracturing, and faulting. It is possible to have more than one kind of strata on display in the same area.

I know from looking at the literature and maps, that the high cliffs surrounding Mewslade Bay are High Tor Limestone Formation (HTL). In the geological succession High Tor Limestone has Gully Oolite Formation (GO) beneath it and Hunts Bay Oolite Subgroup (HBO) above. I noticed a narrow band of what looked like mudstone, low down, and sandwiched between two thick layers of rock that looked slightly different composition and colour. So that set me thinking – while at first I believed the fossils were embedded in HTL, I am now thinking maybe they belong to the Gully Oolite. The Gully Oolite exhibits a palaeo-karst surface elsewhere in Gower (as at Caswell Bay), where the mudstones (Caswell Bay Mudstones) that separate HTL from GO are particularly well developed. Surely the fantastical erosional hollows that characterise Mewslade Bay are also part of this palaeo-karst surface – and the fossils illustrated here are in that particular sculptured rock surface.

Given the uncertainty hanging over the exact identification of the rocks in which the fossils were found, I hesitate to attach names to them. Here anyway is a selection of the fossils I found, which have their own abstract beauty as well as their intrinsic value in aiding our understanding of the environments of the deep past. I will update when I find out more information. As usual, feedback and corrective information is welcome in solving the mystery of the Mewslade fossils.

REFERENCES

George, G. T. (2008) The Geology of South Wales: A Field Guide, published by gareth@geoserve.co.uk.

George, T. N. British Regional Geology: South Wales (1970) Institute of Geological Sciences, Natural Envoronment Research Council, HMSO, 3rd Edition, SBN 11 880084 1.

Howells, M. F. (2007) British Regional Geology: Wales, British Geological Survey, NERC, ISBN 978 085272584 9.

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