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

Bishopston Pill at Pwll Du Beach

Video

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.

Rocks at Clogher Bay 2

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

This is the second in a series of photographs of rocks at Clogher Bay on the Dingle Peninsula in the West Coast of Ireland, and they belong to the Dunquin Group from the Silurian Period. Clogher Bay is just south along the coast from Ferriters Cove which has featured in earlier postings.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.