People fishing from the rocks at Fall Bay on the Gower Peninsula are almost invisible in the amazing beachscape of giant sloping limestone slabs dipping into the sea.
It looked like blood but of course it wasn’t! Red liquid seemed to be oozing from the sand high on the shore towards the north end of Whiteford Sands on the Gower Peninsula in South Wales, approaching Whiteford Point. I have seen the phenomenon before and wrote about a possible explanation in the post “Rusty pebbles at Whiteford”. Only on that occasion the seepage was more orange in colour and clearly ferruginous in nature. Yesterday, the liquid seemed much more concentrated and red, like blood, quite spectacular, but perhaps just a trick of the light. These photographs are as taken and not edited in any way as I am uploading them direct from my i-pad. I believe that the iron responsible for colouring the water draining down the shore is derived from an iron pan caused by decomposition of an ancient peat bed beneath the sand. It is possible to see the layers of peat and clay where they are exposed just below the seepage rivulets. The peat and clay layers are increasingly interesting as more logs and stumps of preserved trees and bushes are weathering out. More about these features in later posts.
The small cove at Pwll Du (or Pwlldu) on the south coast of the Gower Peninsula in South Wales has been created by two fault lines extending approximately northwest to southeast. They converge inland, and separate towards the sea, meeting the shoreline more or less at right angles, with one at the east and one at the west of the bay, running through Carboniferous Limestone strata. The fault lines displace the normal sequence of rock layers so that to the west the rocks are Oxwich Head Limestone, in the middle between the faults it is Hunts Bay Oolite, and in the east it is High Tor Limestone.
Images of the rocks at the east end of Pwll Du Bay are shown in the gallery above. Photographs with details of the rocks at the west end of the bay are given in the gallery below.
Overlying the central area of Hunts Bay Oolite is a massive, multiple-tiered shingle bank which blocks the head of the valley and currently dams the river known as the Bishopston Pill. The shingle banks of Pwll Du will be featured in the next post.
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
Mewslade Bay is one of my favourite beaches on the south Gower Coast. Well-known for its dramatic rock formations and beautiful sandy shore. It has taken a pounding during recent storms. The result of the relentless attacks by wind and waves is a complete transformation – the sand has disappeared! The pictures shown above, revealling the new topography of Mewslade, were sent to me by kind friends from the nearby village of Middleton. They regularly walk their dogs on the beach and captured these shots on an i-pad yesterday afternoon. It seems that this vanishing sand event is a not a unique occurrence. It has happened before but I am not certain how long ago. The good news is that on that occasion the beach eventually recovered and the sand came back.
The images below I took myself. They show how that same part of the shore at Mewslade Bay – the part which is now totally denuded of sand to reveal the underlying wave-cut platform – looked prior to the storms, with deep sand extending up the beach as far as the fault gully that connects it with the dry valley beyond. I am told that an estimated depth of 2 – 3 feet of sand has been washed away and that rocks shattered by the waves lie all around. Many of these rocks no doubt derived from the fault breccia that surrounds the gully. I wish I could be there myself to record the details of this storm-driven revelation of the underlying geology.
It is interesting to note that the sand moves around this whole area on both a short-term and long-term basis – eroding in one area and being deposited in another (May, V. J. 2007). This can be seen (and I have been recording it over recent years) in the way that beach topography changes with deeper or shallower levels of sand, maybe even between tides, as seen from the relationship between fixed objects and the changing levels of sand at Rhossili and Whiteford Sands; also, for instance, by the uncovering of once submerged and buried forest timbers, ancient peat layers, and glacial deposits (like at Broughton Bay). Sand dunes are cut away (for example, at Llangennith and Whiteford Point) and sand banks accumulate.
The sand, however, is a finite resource. The purely mineral part at least is not being formed to any significant degree at the present. The sand deposits from around the Gower Peninsula were left there by melting ice sheets and are a product of glaciation. While glaciers and ice sheets moved down towards the coast, rocks were picked up by the passage of the ice over the ground, and these were responsible for grinding to minute fragments the rock over which they traversed. When the ice started to melt and retreat, the rocks and sand were dumped. This is how the sand arrived in Gower.
There are concerns about the way this valuable resource of sand is being exploited. There are worldwide fears about the impact of removing too much sand from an un-renewable resource. A documentary film has recently been released called Sand Wars – drawing attention to this potential problem.
Click here for more posts about Mewslade Bay on Jessica’s Nature Blog.
COPYRIGHT JESSICA WINDER 2014
All Rights Reserved
These rocks are not pretty but they are interesting! This is the project I am working on at the moment. I am trying to understand the rocks on the west side of Broughton Bay on the Gower Peninsula. I know that they are Hunts Bay Oolite Subgroup of the Carboniferous Limestone from looking at the geology map – but that is just the beginning of the understanding.
Not all the rock looks the same. There seem to be two main parts. The upper part of the cliff looks a bit of a mess, a bit of a jumble, coarse sediments and lots of fractures, ?faults, and various lenses and bands of material. Sometimes it looks like some sort of breccia. It is mostly examples of the appearance of the rock in the upper part of the cliff that are featured in this post. By comparison, the lower part of the cliff tends to be a different colour, is more solid, massive, and continuous, with fewer fractures, and containing obvious fossils.
In this and subsequent posts I am just putting down my thoughts as I read more about the subject. I have already found a couple of good references to help me. What I really need to do is visit the “type location” for this particular rock type, from which this particular subgroup of the Carboniferous Limestone was first properly identified and described. Perhaps the next time I am in Gower. Maybe it will all become a lot clearer then. Meanwhile, I will continue my attempts to identify the components of the rock and understand their origins.
First of all, it should be noted that in the photographs shown here, the orange, yellow, and black patches are modern lichens living on the surface of the rock and are nothing to do with the rock itself. The white colour on the rock close-ups is usually crystalline calcite. The top picture in this post shows the general location where the following photographs were taken, from just before Twlc Point to Foxhole Point on the west side of Broughton Bay. The boulders on the beach at the foot of the low cliff are covered with living barnacles attached to mussels, and by green seaweed.
The Hunts Bay Oolite Subgroup (HBO) is the most recent nomenclature for this type of rock but it was first named and defined as the Hunts Bay Group by Wilson et al (1990). The type section is the cliffs and foreshore reefs between Bacon Hole and Pwlldu Head, Southgate, Gower, South Wales (SS 5604 8674 – 5728 8632).
This is a work in progress and I will amend and annotate the text and pictures as I learn more, as well as adding new posts on the subject! If you, as a reader and expert geologist, know that I as an amateur have made a mistake in my understanding about these rocks, please do drop me a line and put me right.
I am currently reading:
Waters C N, Waters R A, Barclay, W J, and Davies J R (2009) A lithostratigraphical framework for the Carboniferous successions of southern Great Britain (onshore), British Geological Survey Research Report RR/09/01, NERC, Keyworth, Nottingham.
Willoughby, C (1996) Environments of Deposition in the Carboniferous Limestone of South East Gower, Bsc Geology Thesis, University of Wales, Aberystwyth.
Wilson, D, Davies, J R, Fletcher, C J N, and Smith M. (1990) Geology of the South Wales Coalfield, Part VI, the country around Bridgend. Memoir of the British Geological Survey, Sheets 261 and 262 (England and Wales).
COPYRIGHT JESSICA WINDER 2013
All rights reserved