A walk along the shore beneath Rhossili Cliffs

Blue tidal pool water and limestone rock face

From the southern sandy shore of Rhossili Beach in Gower, the cliffs tower overhead, bearing the village itself. Sheep with bright red and purple markings nonchalantly graze the craggy upper slopes. Visitors to the Worms Head Causeway are minute figures among the hummocks of a former castle, peering recklessly over the edge to the beach below.

The path down from the village to the beach has been disrupted by last winter’s land slip, and heavy machinery continues to make a new, easier way to the shore. The red earth scars of the recent and many previous movements are visible along the face of the fault-line valley that separates the Carboniferous Limestone Rhossili headland from the greater height of the Old Red Sandstone in Rhossili Down. Boulders litter the beach at this point. Some loose rocks are red sandstones and conglomerates from the Down. Many of the larger boulders are composed of angular limestone fragments (something to do with glaciation I think – maybe till) held together by a crystalline matrix that formed from calcium-rich groundwater percolating  between the stones. Some boulders are huge chunks of Black Rock Limestone or similar from the headland and must weigh many tons.

Standing far out on the shore allows a panoramic view of the cliffs, from the soft red soil and erratic turf of the land slip area, along the bare rock exposed strata of the basal third of the cliffs, to the tidal island of Worms Head beyond. The cliff face is scalloped in and out by early quarrying activities. The distinct diagonal arrangement of the dipping rock layers contrasts with the horizontal colour banding caused by the colonisation of the rock surface between tide levels by organisms with different tolerances to exposure.

In places, tidal pools of strangely blue water skirt the pale, barnacle and mussel encrusted rock. Sand ripples like the lans and grooves of massive fingerprints decorate the beach, and create intricate arrangements around isolated boulders, reminding me of Japanese Zen gardens. Rounded smooth limestone pebbles in caves and alcoves bear fossil Sea Lily stems. And everywhere, sharp-edged fragments on the beach are evidence for the continuous weathering of the cliff face where each rock fall is signified by the fresh exposure of frequently orange-coloured stone

River Mud Patterns 1

Dendritic patterns in river mud

At low tide, the water draining down through the glutinous soft muds on the banks and bed of the River Hull, near the mouth where it flows into the Humber, carves deep dendritic patterns in the sediments. This phenomenon mirrors the action of large scale river systems in the wider landscape, and is the key to unravelling the complex stratigraphy of sedimentary rocks that have formed in past geological periods through the transport of sediments by rivers in valleys, flood plains, and deltas down to the sea.

Natural dendritic patterns in soft river mud

Dendritic drainage patterns in soft river sediments

Rocks at Ferriters Cove 10

This marks the final post in the series about the rocks at Ferriters Cove. I had spent a happy few hours on the beach and reached the limit of accessible shore at Ferriters Cove. Time to call it a day. At this northernmost part of the shore, the steeply sloping strata in the cliff, with the bedding planes facing outwards as a continuous sheet, at first seem to be buckling under their own weight, as seen in images 55a and 56 in the previous post. Then, just a few metres further on, the strata can be viewed side-on across the bedding planes with the sequence of individual layers revealed. The strata are curved concavely so that the cliff face is like the under-side of a huge wave, the crest of which is curving over and about to crash down and break. You can see this best in images 60 and 61.

There are also some enigmatic markings on that part of the bedrock on the beach which is covered each day by the tide. I wonder if these are fossils. Photo 73 has a number of rounded shapes that look like they might be gastropods; and Bembexia is a marine snail that is recorded in this locality.

More problematic are the plant-like patterns which occur on a number of rocks (see images 79 – 81). They seem to have a central stem with numerous branchlets along the length. I am not at all certain that these are fossils although they seem to be integral with the surface of the rock and to have a slightly different composition which is reflected in the fact that there is no black biofilm (maybe lichen) growing on them. I am fairly sure that the ‘plants’ are not grazing trails left by the feeding activities of the adjacent limpets and periwinkles. Plants are in fact recorded from the Silurian but I cannot find any illustrations that resemble these Ferriters Cove ‘plants’.

In an article about the Silurian Period on the website of the University of California Museum of Paleontology it says:

Perhaps the most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cocksonia, a collection of branching-stemmed plants that produce sporangia at their tips.

However, drawings of that particular genus show a very different branching system to that exhibited by the Ferriters Cove ‘plants’. Maybe I will get a clearer understanding when I have tracked down some of the specialist research papers on the fossils of this area such as those written by C. H. Holland:

Holland, C. H. (1969) Irish counterpart of the Silurian of Newfoundland. Memoir of the association of Petroleum Geologists 12, 298-308.

Holland, C. H. (1987) Stratigraphical and structural relationships of the Dingle Group (Silurian), County Kerry, Ireland. Geological Magazine 124, 33-42.

Holland, C. H. (1988) The fossiliferous Silurian rocks of the Dunquin inlier, Dingle Peninsula, County Kerry, Ireland. Transactions of the Royal Society of Edinburgh: Earth Sciences 79, 347-360.

Rocks at Ferriters Cove 9

Cliff of Silurian strata at Ferriter CoveBy the time I had reached the northernmost edge of the beach at Ferriters Cove, the Silurian rocks had changed their appearance again. The cliff here is higher and composed of a wonderful patchwork of mainly yellow slabs with purple-grey markings. Many of these slabs have fallen to the shore in a thick loose layer. Among these pieces of stone I found some more fossils, internal casts and impressions of brachiopods, including different species to the one I found earlier (I thought that might be Leptaena sp.). Two particular brachiopods are mentioned on the sign at the entrance to the beach, Holcospirifer (bigugosus?) and Rhipidium (hibernicum?), and it is likely that the fossils in images 57b,c,& d belong to one or both of those species. I am wondering if the much larger regular rounded fossil in image 57a is a species of Atrypa.

REFERENCE

Bassett, M. G., Cocks, L. R. M., and Holland C.H. (1976) The affinities of two endemic Silurian brachiopods from the Dingle Peninsula, Ireland, Palaeontology, Vol. 19, Part 4, pp. 615 – 625, pls. 93-95.

Rocks at Ferriters Cove 8

Natural abstract design in Silurian rock at Ferriters Cove

Water-worn, soft, and stripey Silurian sedimentary rocks make sporadic appearances through the sandy beach at Ferriters Cove and sometimes they can have a strangely sculptural appearance, or even of a landscape in miniature, depending on the perspective from which they are photographed. I also particularly like the pale blue-green colour contrasting with the muted yellow that contributes to the natural abstract striped designs.

You can click on an image to enlarge it.

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Rocks at Ferriters Cove 7

Natural pattern, shape, and texture in Silurian bedrock at Ferriters Cove

The last part of the Silurian strata exposure of the small rocky promontory at Ferriters Cove, before the wide sandy strip with beach stones, is very abstract…. but not so sculptural in appearance as the patches of water-worn mudstones that emerge here and there through the sand – see the next post!

Beach Stones at Ferriters Cove

View of Ferriters Cove on the Dingle PeninsulaBetween rocky outcrops and promontories at Ferriters Cove lie stretches of sandy beach with patches of water-worn beach stones and smaller pebbles. The stones are derived from a variety of Silurian strata, not only from this cove but also from the coast further to the north which is also composed of Silurian Period rocks.