Rocks & Pools on Worms Head Causeway

Looking down to the Worms Head at high tide

It was a sunny day with the prospect of a very low tide – just right for exploring the rocky causeway that links the Rhossili headland to the tidal island of Worms Head. I was really looking forward to it. The times when it is safe to venture out on the Causeway are always clearly indicated; and it is assuring to know that there is almost always a Coastguard Lookout monitoring the area through binoculars to render assistance if anyone gets into trouble out on the rocks. Most people seem merely to cross the causeway by the quickest route to reach the Worms Head. However, the Causeway itself is a source of great fascination for anyone like me and interested in natural history.

You have to be fairly fit to get down on the Causeway and need to have sensible footwear. The descent from the red-rimmed turf platform at the base of the headland, and the initial scramble over the tall projecting limestone strata of the first 50 metres or so, can be a challenge for some. However, it is well worth the effort because it is a different world out there. It is a unique experience. An alien landscape full of surprises awaits you.

When you look down on the Causeway from the headland , it might look a rough and barren expanse of dull buff and grey rocks. Boring, even. Once down of the rocks, a closer perspective reveals a wealth of detail with hidden pockets of colour, variations in texture and topography, strange natural sculpturings, ancient rocks with complex geological histories, embedded fossils such as entire Sea Lilies, tidal pools of every size, deep water gullies, multi-coloured seaweeds and myriads of seashore creatures. The variety and complexity of this beachscape might be perplexing but it is none the less inviting and exciting.

On this particular visit, I aimed for the central part of the Causeway that I hadn’t investigated before, and then slowly veered round in a more easterly direction before returning to base. I was interested not only in the geology and the seashore life as entities in their own right but was also intrigued by the way each component of the shore is influenced by the other – the way everything interacts. How the geology and landscape affect and facilitate the living organisms; and how the living organisms affect the landscape.

Once away from the very landward edge of the Causeway where the rocks can sometimes seem to be completely devoid of animal life, almost every rock surface is covered to a varying degree by small acorn barnacles of different types. The common mussel is abundant but not growing in such profusion as in previous years. Not many dog whelks were feeding on the barnacles and mussels along the route I was taking but, no doubt, they lurk in other lower shore areas. Large limpets cling to surfaces both wet and dry. Common Periwinkles and striped Top Shells are common. Even the smallest pool is home to red Beadlet and pink-tipped Snakelocks Anemones. Small fish and shrimps dart through the pools and hide beneath the seaweed. Large Balanus perforatus grow on the lower shore  – instantly recognisable with their volcano-shaped shells and beaky opercular plates.

While I was sitting eating my lunch, a large Common Green Shore Crab ventured out of the water right by my feet but soon made a hasty retreat. I made a little movie of him scuttling around the pool.

Even the most exposed rock surfaces out on the centre of the Causeway have some seaweeds growing on them. Bright green soft weeds of the Ulva species (like Sea Lettuce and Gutweed) seem to tolerate the dry rock as well as the pools. Red branching seaweeds make a dramatic colour counterpoint to them: they often grow together. Calcareous red seaweeds like the branching Coral Weed grow extensively, and patches of flat Corallinaceae crusts like Pink Paint Weeds line water-filled hollow basins and dips, and coat the water-line of large boulders in the gullies. The familiar Brown Fucoid seaweeds like Bladder Wrack and Toothed Wrack make an appearance further down the shore, while the large kelps such as Oarweed occupy deeper waters right on the shoreline and below. One interesting new alga that I spotted is an encrusting brown paint-like species covering the shells of limpets (probably Brown Limpet Paint, Ralfsia verrucosa).

The strange curvilinear shapes of some of the upstanding rocks, the deep gullies along bedding planes, and the numerous rounded hollows and depressions, are typical of coastal limestone karst topography. More extreme and more extensive examples can be seen elsewhere in Gower, such as around the tidal island of Burry Holms, and at Mewslade Bay and Caswell Bay. Many people assume that it is the impact of waves, acid dissolution by rain, and abrasion by sand-bearing winds, that are the combined means by which seashore rocks are worn away, slowly and steadily over the millennia. This is partly true; it does account for some of the erosion. However, there is another aspect to the erosion of seashore rocks which is equally, maybe more, important: bio-erosion.

It all starts in the smallest of ways on a microscopic level with organisms like bacteria, algae, fungi, and lichens – especially those that are capable of not only colonising the surface of the rock (endolithic organisms) but also of penetrating it (epilithic organisms), even if that is only to a depth of a few millimetres. The general effect of the rock penetration is a weakening of the substrate so that when grazing molluscs like periwinkles and limpets come along they can easily remove not only the bio-film on the surface but can also scrape off some of the surface rock as well.

For example, analyses of the gut contents of limpets shows that small particles of rock are ingested along with the food they obtain. Limpets also alter the rock in another way. They always return from foraging trips to the same position on the rocks – their home base. As a limpet adjusts its position on the home base, its shell mechanically grinds against the rock wearing away a circular depression; this depression is deepened and emphasised by the chemical effect of the limpet’s acidic waste products dissolving the rock. It has been calculated that over vast periods of time, the cumulative effects of limpets feeding on rocks can contribute the process by which they are reshaped or destroyed. Abandoned limpet home bases are common on the rocks of the Causeway where the animals have been dislodged by last winter’s stormy seas.

Another major bio-erosional component is the burrowing activity of marine polychaete worms, and of specially adapted rock-boring bivalved molluscs. It is amazing to see just how extensive is this kind of damage to the rocks on the Causeway. It is no wonder that there are so many pebbles and boulders with holes in them found on the shores all around the Gower Peninsula. Almost every damp patch, depression, hollow, pool, and gully has limestone riddled with these burrows. The burrowing activity of these marine invertebrates is made easier by the weakening of the rock by micro-organisms; and the burrows and holes then provide a greater surface area for the further colonisation by micro-organisms. The combined effects of all types of bio-erosion have a significant impact on the surface shape of the limestone and landscape.

The strata on the Causeway lie in parallel lines along an approximately northwest to southeast axis. Most of the rocks that you see are Black Rock Limestone Subgroup with some Shipway and Brofiscin Limestone. As you face the Causeway with your back to the Coastguard Lookout building on the Rhossili headland, then behind you and beneath the superficial loose deposits, lies first of all Gully Oolite and then High Tor Limestone as solid bedrock. In front of you, the Black Rock Limestone is bordered on the far side of the Causeway by strips of first Gully Oolite and then outermost High Tor Limestone solid bedrock. So there is a particular sequence to the layers of rock visible on the surface which reflects their history.

On the landward side of the Worms Head Causeway, the sharp projecting edge-on rock strata dip down and towards the Rhossili headland and lean at an angle in the direction of the open sea. On the seaward side of the Causeway, the lines of strata dip down and towards the open water with their free edges inclined in the direction of the land. Between these two areas of strata that point towards each other, there is a flatter, more eroded area, more severely cut away by wave action. The whole unit is the remains of an eroded geological feature called an anticline.

Imagine that the sedimentary rock layers were originally horizontal but later pushed upwards by earth movements into a mound or ridge; the resulting arched rock layers in the mound have been worn away by the elements over time until only the base of the mound remains with a characteristic layout in which stumps of the most recently formed younger rocks lie on the outside with the older layers on the inside of the feature.

You can visualise this process by thinking of a Swiss Roll. [If I am to persist with this analogy, perhaps we can go whole hog and imagine a chocolate one with cream filling?] If the cake were roughly cut  length-wise, the broken surfaces would have a pattern of longitudinal stripes with alternating sponge and cream. The layer which was original wrapped around the outside of the Swiss Roll cake would be seen as the two stripes of sponge on each side.

There is rocky shore zonation of the organisms that live on the Worms Head Causeway but this zonation is not so straightforward to recognise and interpret as on a normal stretch of shoreline. For a start, the Causeway is connected by beaches to the mainland at the Rhossili headland and the island at Worms Head. Elsewhere, the waters’ edge describes an irregular outline, the shape of which depends on the state of tide, and which more or less defies description. The surface is full of ups and downs on various scales.

Zonation is the way that organisms tend grow in associations on rocks depending on their tolerance for different degrees of exposure to the air – each type of organism having a physiological preference or need for more or less immersion in sea water. Typically, this zonation of organisms is seen on a rocky shore as different coloured bands – pale for barnacles, dark for mussels, yellow for lichens and so forth.

The best way to describe the zonation on the large scale out on the Causeway is by thinking of it radiating irregularly outwards, in a roughly concentric fashion, along a slight and highly disturbed incline from the highest to the lowest parts of the Causeway  – rather than a zonation with easily observable regular bands as on a normal rocky shoreline or cliff face. On a minor scale, there is zonation in the rock pools and in the water-filled gullies themselves.

At high tide the causeway is completely covered by the sea; sometimes the beaches are covered too. As the tide goes out, greater and greater areas of the causeway rocks are exposed to the air. It could be claimed that the water drains away from the perimeter and also from higher areas of the Causeway simultaneously. Water seems to continually make its way downwards from pools in the highest parts, through small cascades and gullies, to reach the sea. You can hear the continuous trickling sound of this water, merging with the noise of the wind, the breaking waves, the calls of birds. You are immersed in sound when you are out on the Causeway.

The tide seems to come in and go out in a very haphazard way. It is difficult for the occasional visitor to predict the direction in which the seawater will ebb or flow; or the speed with which it will rise and fall. This is what makes it potentially dangerous to be out on the Causeway when the tide is in flood – it could be difficult to decide which parts will be covered with water first, and therefore it is easy to get trapped by the water, with access denied to dry land. Swimming or even wading through the tide water is not a good idea because of the cross currents, water encroaching from three sides, and the hazardous sharp and barnacle-encrusted rocks beneath your feet.

Having kept an eye on the changing tide after spending a most enjoyable five hours out on the Causeway exploring and taking photographs, I looked for a safe, or easy way to get back to the Rhossili headland. The strata run in rows parallel to the headland and projecting higher and higher as you approach the beach. There are numerous pools between the layers of rock. This would make it hard work to traverse the last bit of terrain back to the beach from the location I was in. Luckily, north-south fault lines cross the rock layers. The areas of the fault lines tend to be worn down to lower levels than the surrounding projecting rocks because they are frequently filled with wide veins of softer white crystalline calcite and narrow veins of red haematite. Following these fault lines makes it much easier to negotiate a way back to the mainland.

The surfaces of these natural pathways are often worn smooth. Shallow streams of sea water flow along them and many small seashore creatures take advantage of the moist habitat they provide. The ‘stream’ beds and shallow pools along the fault lines are really colourful, often coated with a film of bright green microscopic algae that provides a vivid contrast to the red and white minerals, and to the purple striped Top Shells that love to graze there.

From out on the Causeway, not only can you view Worms Head from the most unusual angles and see it in a way that is completely different from the standard postcard perspectives – but there are also spectacular views of the Rhossili headland. The sixty metre high plateau of clearly stratified limestone is sketchily cloaked with turf which at its lowermost weathered edge reveals a vivid orange soil. This soil covers remnants of an ancient raised beach where seashells and pebbles from around 125,000 years ago, deposited in the Ipswichian Interglacial period, are cemented together by calcite and covered by glacial debris. The orange band contrasts dramatically with the bleached smooth pebbles and bizarre barren outcrops of the beach itself. This is the point to which I at last returned and was able to look back at the vast expanse of rocky causeway fully revealed by the now low tide. Next time I intend to venture out to the deep gullies of the far side of the Causeway and see what I can find there.

P.S. Don’t forget that you can click on any picture to enlarge it and see a description of the image

COPYRIGHT JESSICA WINDER 2014

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Evening Tide Rhossili – videoclip

Rocks and Pools on Burry Holms

The fantastically sculptured Carboniferous limestone around the tidal island of Burry Holms, which lies at the northern end of Rhossili Beach on the Gower Peninsula in South Wales, provides a habitat for many intertidal species.

The exposed rocks between the highest and lowest tide levels are covered with a patchwork pattern of permanently attached dark mussels and pale acorn barnacles on which thousands of roaming dog whelks feed. Periwinkles and limpets graze on the algal films that cover the rocks and the shells. The curiously curving contours of the rocks supply numerous sheltered micro-habitats in the form of small hollows, crevices, gullies, overhangs, and pools.

Some of the pools are only just big enough to accommodate a couple of sea anemones and a few dog whelks. Some bigger pools are almost perfectly circular smooth basins dissolved into the stone, characteristically highlighted in summer by vivid green soft seaweeds concealing minute fish and multitudes of striped top shells and other gastropods. The occasional deeper pool  becomes a safe haven for clusters of common starfish and small shrimps; while wet overhangs and clefts display numerous beadlet sea anemones in a vast array of colours from pale khaki to bright red, together with rounded mounds of orange sponge.

All the organisms that live on the rocks in the inter-tidal zone contribute to the process by which the rocks are shaped. Frequently, this is done in a slow, subtle, and imperceptible way by the actions of epilithic and endolithic micro-organisms such as bacteria, fungi, algae, and lichens, and by the way these microscopic organisms are scraped from the surface and surface layers of the limestone by grazing seashore creatures.

Sometimes, the erosion is visible to the naked eye – as in the circular “home bases” that limpets have created by the continual grinding and wear of their shells against the rock as they settled in the same place each time after foraging trips; together with acid dissolution of the stone by their waste metabolic by-products. Another easily observable kind of bio-erosion damage is the burrowing activity of marine polychaete worms and boring bivalved molluscs. These small holes in rocks are often clustered in a band immediately above and below the water line of pools but also in any continually wet or damp grooves and channels. The overall persistent erosional activity of marine invertebrate organisms on intertidal seashore limestone over thousands and even millions of years contributes to the creation of fascinatingly sculptured karst topography like that seen around the island of Burry Holms.

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Evening Tide Rhossili

COPYRIGHT JESSICA WINDER 2014

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Large Jellyfish at Rhossili

 

Yesterday (27th July 2014) I walked along Rhossili beach from one end to the other and back again – a distance of about 10 kilometres. I followed the high tide strand line most of the way and saw 16 large Barrel Jellyfish, also known as Dustbin-lid and Root-mouthed Jellyfish (Rhizostoma octopus Linnaeus) – but there could have been more. They were various sizes and states of maturity. I put a seashell beside each one I photographed to give an idea of scale. They were different shades of pink and blue colour. Their condition varied, too. Some were freshly dead and well preserved but others had been split or torn, and some were beginning to decompose by “melting” into the sand. They were lying at different angles. Some were dome upwards and others were upside down. All are harmless – no danger from stings to holiday makers. They are a relatively common sight on beaches of the Gower Peninsula in South Wales. However, they have been appearing in very large numbers along the Coast of Devon and Cornwall this summer, which is an unusual occurrence, and there has been a lot of coverage of the phenomenon in the media. There are more posts about Barrel or Dustbin-lid Jellyfish elsewhere in Jessica’s Nature Blog from sightings in previous years on Gower.

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A Walk to Mewslade Bay

It is sheer delight from the moment I walk out the door of the one-up one-down cottage known as The Slope. In May, the house martins fly right past carrying food to the youngsters in the coal shed; while the clematis and honeysuckle flowers on the fence provide a safe nesting site for blackbirds. A few yards more and the still pond at Mewslade View is home to beautiful blue iris. The field is covered in lush grass with blossoming plantains; this is the field that is mowed for the Caravan Club visitors to park. Beyond, a flock of sheep clear Nitten’s Field for a re-seeding of wild flowers that will supply food for migrating birds. This year there will be extra red poppy flowers planted to commemorate the centenary of World War I.

The boundary between the private land of Nitten’s Field and Mewslade valley is marked by a stile made of driftwood. From this point you can see right down into the steep-sided dry valley that leads to the sea and Mewslade Bay. The shape of the valley is partly due to it lying along a geological fault line, and partly due to quarrying activities in times gone past. Once the stile is negotiated, you are on public footpaths that lead in various directions. – the coastal path that follows the cliff tops in both directions along the southern shore of the Gower peninsula; back up the valley to the village of Middleton; or down the slope to the bottom of the valley and the beach. The scree-covering on the lower slopes is the result of peri-glacial activity. Access to the shore is via a narrow rocky fault gully but only at low tide as the sea comes right up the gully at many high tides.

If you arrive too early to get on the beach because of the tide, you can walk around the valley sides finding wild flowers and exploring the small caves high up the slopes. From a high vantage point looking east, you can see the dipping rock strata beneath Thurba Head. Looking in the other direction towards Fall Bay, Tears Point, and Worms Head, the high-tide waves lap the jagged dark rocks that project into the sea – Carboniferous limestone with numerous pits created by bio-erosion into a karstic landscape.

The ripping and tearing of the rocks along the fault-line has created some very interesting geology at the gully, with many rock types embedded in white crystalline calcite. This fault breccia can be seen in the solid rock of the gully and in large boulders on the ground. The force of the pounding sea has worked away over the years to carve out interesting tunnels, arches, caves, and blow holes around the entrance to the bay.

As the tide begins to recede, you can see small seashore creatures that cling to the rocks – invertebrates like limpets, barnacles and small periwinkles taking advantage of every nook and cranny.

When at last the tide ebbs, you can get onto the beach. This shore has seen dramatic changes in preceding months. By May this lovely family-friendly sandy beach was recovering nicely after seriously strong seas whipped all the sand away in the first few months of the year. At that time there was nothing but a jagged rocky platform, with a revelation of strata and fossils that most people had not seen before in their lifetime. It wasn’t an altogether unique event for Mewslade – it has been recorded before – but it was a rare circumstance. Mewslade was not alone in suffering this albeit temporary fate. Beaches along many British coasts were severely eroded. Many, like Mewslade, have recovered but some have been changed for ever.

Where the sand has not quite reached its former levels, a white band of crystalline calcite remains exposed at the base of one of the bio-eroded limestone cliffs. Across the shore, numerous rocks with fantastical sculptural shapes are scattered – their forms resembling the peaks and troughs of whipped meringue or cake frosting. Some of these rocks contain fossil corals, bivalves, and marine snails.

I can’t wait to discover more about this fascinating place on my next visit.

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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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Re-appearance of a Rhossili Wreck

Shipwrecked wooden boat on the beach

The shifting of the sands at Rhossili Bay has uncovered a wrecked wooden ship quite high on the shore between Diles Lake and Spaniard Rocks. I last saw this ship’s timbers emerge from the sand about seven years ago. It comes and goes and seems to be a fairly rare sighting. Mostly, the remnants of the keel with its attached ribs lie hidden from view, buried under the sand. However, following the weather events of the winter just past, the sands have moved around to a significant degree and revealed once more this elusive piece of history. I am not even sure of its name.

Of course, Rhossili Beach has seen many ships come to grief. The most famous of all is the Helvetia which features so prominently in all the postcards, pictures, and publicity material for the beach. However, there are many others: the stark rusty metal girders and plate of the Danish ship Vennerne at the base of Rhossili Cliffs; the massive anchor of the Norwegian barque Samuel lying on the Worm’s Head Causeway; and at low spring tides, the engines of the wooden paddle steamer City of Bristol – these are all easy to spot.

My favourite wreck though is this particular one lying near the dunes of Llangennith Burrows. I am delighted when circumstances conspire to enable a view of its old weathered and worn timbers. Wooden pegs form part of its original construction but these were reinforced later with iron nails which have now rusted and stained the woodgrain. Beach pebbles form a drift against the outside of this skeletal hull, and stick between the ribs; while the hollow within makes a transient tide pool.

See the image below for a view of the wreck when I last saw it in 2007.

Remains of wooden ships ribs from a wreck buried in sand

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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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