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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Shoreline Changes at Llangennith Burrows – Part 1

Sand dunes at Rhossili in May 2012

When there are especially dramatic events, like the severe winds and storms of last January and February, that destroyed coastal railway lines, caused major landslips, created disastrous flooding, and removed entire beaches of shingle and sand, everyone becomes aware of how vulnerable our coastline is to extreme weather events. However, visiting the same seashore locations many times over the past ten years, and making a detailed photographic record of animals, plants, sediments and rocks, has enabled me to see changes gradually and steadily taking place as well as resulting from these recent extreme events.

This is the first in a series of posts about changes in shoreline topography, sometimes due to accretion of sediments, sometimes resulting from erosion, that have been changing the way the seashore looks. These changes have an impact on the whole coastal ecosystem, affecting plant communities, the invertebrates that colonise the seashore, and the people who use and enjoy the shorelines.

I have been trying to find among the many images in my collection, those which show recognisably the same place, to illustrate what the location looked like originally, some of the details of the transition if any, and what the location looks like now. In this post, the location is the seaward-facing sand dunes belonging to Llangennith Burrows, at the north end of Rhossili Beach, approaching the tidal island of Burry Holms. The position is “fixed” by a vertical wooden sign indicating one of the designated footpaths that cross the Burrows.

In the first photograph, shown above, the wooden post has had some bright orange plastic flotsam tied to it with rope, to increase its visibilty from low on the sandy beach. The picture was taken on the 16th May 2012. Wind-blown dry sand forms a continuous and gradual incline from the shore to the top of the dune. The dune is stabilised by marram grass. Pebbles at the base of the dune are only just visible beneath the layer of sand. The footpath passes to the right of the signpost, forming a shallow depression on the sky-line.

The image immediately below shows the same location two years later on 6th May 2014. The signpost lacks the orange flotsam now but the footpath can still be seen to the right of it, forming a steep gouge in what remains of the dune. The seaward face of the dunes has been reduced in places to a near vertical surface showing stratification of the established dune. Mobile sand deposits are almost entirely absent. Much of the marram grass has fallen down as turf clumps or disappeared. Pebbles are clearly exposed at the base of the dunes.

Sand dunes at Rhossili in May 2014

Of course, the changes started long before May 2012. The sea has been nibbling at the compacted sand of the dunes for a while, and in between times, the loose sand moves in, out, and all around the beach, sometimes from day to day, and even from tide to tide. However, the hard stratified sand in the dunes has been steadily and inexorably receding. The following pictures show in a bit closer detail what the same area of the Llangennith/Rhossili dunes was looking like at one point (12th December 2012) in the interim period between the times that photographs 1 & 2, and 3 & 4  were taken.

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Flowers on Gower’s Llangennith Marsh

 

A selection of the wonderful spring flowers that grow on the marsh at Llangennith, and at the base of the stabilised dunes that separate the marsh from Llangennith Burrows and Rhossili Beach on the Gower Peninsula in South Wales. I have also included some pictures of the gorgeous Gower ponies that were roaming in small groups, grazing on the new growth of marsh vegetation, and shedding their thick winter coats. This area is crossed by public foot-paths and forms part of the Wales Coast Path.

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More pebbles at Rhossili after storms

More pebbles are visible on the beach at Rhossili on the Gower Peninsula since last winter’s storms. Of course, they were always there but not so many on show. Lots were hidden beneath the sand. The greater number of pebbles is noticeable as soon as you arrive at the beach via the path through the dunes from Hillend campsite. Looking north towards Burry Holms, and south towards Worms Head, a wider band of pebbles than usual is immediately noticeable at the top of the shore.

As you walk towards Diles Lake, which is the stream that flows across the shore from Llangennith Marshes, the pebble layer deepens into a wide bank that more or less dams the stream. This place is subject to frequent change as a result of changes in weather, tides, and currents. It can sometimes be difficult to cross, especially in winter. Right now though, crossing is easy because the stream mostly runs beneath the pebbles, with only a narrow watercourse visible on the surface. It is clear that not only are more pebbles around because sand has been washed away from them but also the pebbles have been pushed up the shore with great force.