Beach Stones with Iron at Rhossili

A beach stone made of iron on the Gower Peninsula in South Wales

When you visit a place often enough, you think you have seen all there is to see. For all the photographs of rocks and pebbles that I have taken over the years, I don’t think I had ever noticed so many stones made of iron as I did on my last trip to Rhossili on the Gower Peninsula, South Wales. Mostly they were lying in the narrow strip of pebbles, cobbles, and boulders that is exposed on the upper reaches of the sandy shore, right at the base of Rhossili Down.

Some of these iron stones appear to be made entirely from iron (maybe iron carbonate) while others were sedimentary rock with a solid iron centre, or with groups or bands of small iron nodules. One stone was stratified with black and rust layers. All of them were very heavy and many exhibited concretionary layers. I know very little about these stones. Their forms of iron are distinctly different from the haematite form that I have previously shown in other blog posts about Gower geology, and from the iron pyrites nodules I have featured from Dorset’s Jurassic rocks. Those stones with groups or layers of smaller nodules look like the siderite form of iron that I photographed at Joggins in Nova Scotia. Iron is recorded in Lower Carboniferous rock strata and also in the Coal Measures higher up in the geological sequence, so iron stones on this Gower beach make general sense but they may have been transported there from another location. Clearly more investigation is required.

Pebbles at Whiteford (4)

Pebbles, shells, and a feather on the beach near Whiteford Point

A sand bar spreads southeast from Whiteford Point in Gower, South Wales. At low tide in the Burry Estuary, it is part of a very extensive sandy area over which cockle and mussel fisherman can traverse in vehicles from places further along the north Gower coast. The sand depth is variable and mostly envelops a spit of pebbles. Sometimes the pebbles are entirely hidden. Sometimes they are partially exposed. Intermixed with the pebbles are seashells – cockles, mussels, whelks, and oysters are the most commonly occurring. There is a wide range of colours and textures in the pebbles and they are particularly interesting because of the range of rock types they represent.

As you take a 360 degree scan of the horizon from this isolated expanse of sand and pebbles, there is not a single rocky outcrop in sight. So where have these beach stones come from? The collection includes sedimentary rocks from the locally occurring Carboniferous limestone and Devonian sandstones, mudstones, and conglomerates – like the bedrock exposed at Rhossili and at Broughton Bay. It also includes samples from higher up in the Carboniferous strata such as the Millstone Grits, sandstones, and shales, and Coal Measure layers. These strata underlie the Burry Estuary into which this spit extends, east Gower, and the Swansea district and way beyond. There are many rock types with which I am not familiar but I notice that some are metamorphic and igneous in nature. So how have all these rocks ended up on this spit, far from their place of origin?

Part of the answer is undoubtedly the effect of sea drift, currents, and storms carrying weathered and broken stones along the shores of Carmarthen Bay and into the estuary or inlet – but a significant proportion of the stones are thought to have been brought to the area from considerable distances away by glaciation, and deposited by the melting of an ice sheet, possibly in the late Devensian era about 24,000 years ago. Most of these stones lie hidden in a mass beneath the Whiteford Dunes but some are exposed high on the shore at the foot of the dunes, and beneath the disused iron lighthouse on Whiteford Point. Over time the waves have dislodged the often frost-shattered stones from the surface of the deposit, and washed them further along the beach around the Point to form pebble spits and banks, in the process smoothing and rounding them into the pebbles visible today.

Click here for more posts about Whiteford Sands, Whiteford Point, and Whiteford Burrows.

Pebbles at Manorbier

Brightly coloured pebbles on the beach at Manorbier in South Pembrokeshire, Wales, with patterns of reflected light under clear sparkling water in a gently flowing stream.

Coloured pebbles under water on a sunny day

Coloured pebbles under water on a sunny day

Coloured pebbles under water on a sunny day

Coloured pebbles under water on a sunny day

Coloured pebbles under water on a sunny day

Pebbles with Lichen at Chesil

Bright orange lichen encrusting a beach pebble in a sheltered zone

On the eastern flank of the great pebble bank of Chesil Beach in Dorset, on that part adjacent to the Fleet Lagoon where fishermen’s huts are strewn along the water’s edge, the pebbles were sufficiently undisturbed in the spring of 2011 for vegetation to get a grip. A few scattered plants had established themselves amongst the rounded stones; and many pebbles in the same area were coated with slow-growing black or bright orange lichens.

This type of colonisation of beach shingle is a fairly uncommon phenomenon because, in general, the constant movement and abrasion of the pebbles does not allow plants to establish a root system or lichens to encrust the surface of the pebbles themselves. However, in this particular location on the leeward sheltered side of the pebble bank, there had been a period of years of relative stability that enabled vegetation to start growing.

During the winter of 2013 to 2014 the Chesil Bank sustained enormous damage from the storms. The wave action resulted in massive movements of the pebbles. I haven’t revisited the site since the storms but I strongly suspect that the plants and lichens will have suffered and may no longer exist. I must go and check it out. Whatever the outcome of last winter’s weather and subsequent maintenance work on the pebble bank, the slow colonisation process will surely begin again but will take time to restore the habitat to its former situation.

Pebbles with patches of black lichen on the Chesil Bank in Dorset

Pebbles with patches of black lichen on the Chesil Bank in Dorset

Pebbles with patches of black lichen on the Chesil Bank in Dorset

Plant growing on pebbles at Chesil Beach

Plants and bright orange lichen growing on beach pebbles

Pebbles with patches of black lichen on the Chesil Bank in Dorset

Makeshift boardwalk up the Chesil Bank in Dorset

Groynes on Rosslare Strand

On Rosslare Strand in Ireland, a series of groynes transects the beach to prevent loss of sediments from the shore. Most of these sea defence groynes are constructed as a row of wooden posts embedded deep in the sand. Over time, the posts have been weathered and whittled down to varying degrees, dependent on their position and exposure to wave action. Some rows still stand knee-high, festooned with seaweed and fishing lines, but others have been worn down to mere stumps. The eroding posts reveal intricate wood-grain patterns, and have sometimes become narrow and tapered with wear, thus opening up gaps in the line that become traps for wave-driven pebbles.

Bishopston Pill at Pwll Du Beach


This short video clip shows two streams of water gushing from the base of the large multi-tiered shingle bank that blocks the valley at Pwll Du Bay in Gower, South Wales. The water comes from the Bishopston Pill river that flows down the valley to the shore, but which has been dammed up behind the shingle. In summer, reduced water flow means that just a trickle seeps out of the shingle base and spreads across the shore. This video was taken in October after heavy rain had increased the quantity of water in the river and subsequently the pressure of the small lake behind the pebble bank. There is a fast and steady flow and the two streams have begun to create channels through the pebbles before converging on the beach. Apparently, in winter, the build-up of water pressure behind the bank means that the river cuts its way straight through to the sea.

Shingle Banks at Pwll Du

View looking east across the water's edge at Pwll Du Bay

Long before the beach was actually visible, the thunder of the waves crashing on the shore, and the grinding of the pebbles against each other on the water’s edge, could be heard as I followed the signpost from Pwll Du Head, down the steep path through the tree-clad valley side to the shore below.

Stretched across the mouth of the valley below lies a massive bank of cobbles and pebbles, or more accurately three successive banks. Unusually for this type of beach, almost all the rocks that make up the banks are the waste product of quarrying activity. Certain privileged farming tenants up until the beginning of the 20th century were granted rights of “cliffage” that allowed them to quarry limestone from the valley sides and the eastern cliff face of Pwll Du Head. The quarry on the Head ceased operation in 1884. The workings are now mostly overgrown.

Boulders from the quarries were placed in heaps marked with wooden stakes on the beach. Ships came over from the north Devon coast to collect the stone to be burnt for lime that would fertilise the fields. Apparently, when the boats arrived, they would scupper in the shallow water at high tide next to the marker posts. Once they were in position on the bottom, the sea-cocks were closed again, with the boat remaining full of water as the tide went out. This technique meant that the bottom of the boat would not be damaged because the water cushioned the fall as the first of the quarried boulders were thrown aboard. Once the cargo was loaded, the sea-cocks were opened to drain away excess water, then closed so that the boat could float on the next high tide ready for the return trip to Devon. Small pieces of rock were too bothersome to load and remained on the shore, gradually building up over the years into the banks.

The shingle banks block the flow of the small river known as Bishopston Pill. The barrier of the shingle banks forms a dam. A small lake lies behind the banks. Beyond the pooled water in the pictures below, two white buildings are tucked into the western valley side at the back of the shingle; these were once public houses that catered for the workmen labouring in the quarries – it must have been thirsty work.

In summer when flow is reduced the water seeps gently from the base of the banks and spreads out across the shore, usually at the eastern end of the beach. When I visited in October after heavy rain, the water was emerging in two fast-flowing streams that were cutting embryo channels through the shingle at the seaward face. In winter when flow is greatest it seems that the banks are breached completely by the flow.

The pebbles nearest to the shore, where they are constantly moved against each other by the waves, tend to be the smallest and smoothest. Most of them are the local Carboniferous limestone but some “foreign” pebbles are included and these originated as jettisoned ballast from ships plying trade in the Pwll Du quarried limestone.

As you walk inland across the shingle, the nature of the stones beneath your feet changes. Whereas on the shore small rounded pebbles tend to predominate, further inland the stones increase to cobble size and they become progressively less rounded and more angular. The shingle bank is always a dynamic structure. However, for many years the innermost couple of the three terraces or ridges, storm beaches, were relatively stable. The stability partly enabled and partly resulted from vegetative colonisation.

I have read accounts of lichen-covered pebbles on the inner banks but none were visible when I visited. Although this was my first visit, I have seen earlier accounts of this locality, and I think that last winter’s storms may well have had a profound effect on the shingle banks. It seemed to me that there had been a great churning up of the stones, resulting in a greater mixing of size and shape, possibly a partial reconstruction of the ridges, destruction of some of the patches formerly stabilised by rooted plants, and removal of lichen encrustations or burial of lichen coated pebbles.


Gillham, M. E. (1977) The Natural History of the Gower, South Wales, D. Brown and Sons Ltd, Cowbridge, ISBN 0 905928 00 8.

Mullard, J (2006) Gower, New Naturalist Series, Collins, ISBN 0 00 716066 6.

Pwll-Du and the quarrymen of Gower The Geological Society Website

Sea-washed Carboniferous limestone pebbles at Pwll Du Bay