Rocks & Pebbles near Twlc Point

Posted on May 15, 2017 by winderjssc

Pebbles near Twlc Point at Broughton Bay on the Gower Peninsula in South Wales

Rocks and pebbles near Twlc Point at Broughton Bay on the Gower Peninsula in South Wales

Detail of the pattern in a beach boulder at Twlc Point

Beach boulder and pebbles at Twlc Point in Gower

View from Twlc Point in Broughton Bay, Gower.

Fossilierous beach stone at Twlc Point in Broughton Bay, Gower, South Wales

Broughton Bay is a wide sandy expanse on the north shore of the Gower Peninsula in South Wales, facing the Loughor Estuary or Burry Inlet. A small promontory called Twlc Point at the western end of the beach has an interesting geology with an exposure of Hunts Bay Oolite from the Carboniferous Period. I have written about these strata in earlier posts such as:

Rocks on the west side of Broughton Bay Part 1

Rocks on the west side of Broughton Bay Part 2

Rocks on the west side of Broughton Bay Part 3

Brachiopod fossils in Hunts Bay Oolite at Broughton Bay

On this particular visit I was content to appreciate the way that pebbles of many types and colours on the upper shore were clustered around outcrops and boulders of the limestone which were often pink-tinged and sometimes fossiliferous.

Pebbles at Langland Bay

Posted on February 17, 2016 by winderjssc

The pebbles at Langland Bay are all sedimentary rock as far as I can see but they include many different rock types from shores further away. Red and green Devonian sandstones, siltstones and conglomerates; light and dark bluish-grey Lower and Upper Carboniferous Period limestones (some with fossils), and shales; Namurian sandstones, grits, shales and coal measures with black and iron-bearing deposits; and no doubt the occasional erratic brought in by the ice sheets in periods of glaciation. Consequently there is a great variety of colours, textures and patterns. Pebbles with holes made by sea creatures such as piddocks or other boring bivalved molluscs, or by marine polychaete worms and sponges are also a frequent occurrence. The pictures show the pebbles mostly in the the positions where they were found although I may have moved the odd one or two.

Pebbles from Carboniferous Period rocks at Langland Bay

Beach Stones with Iron at Rhossili

Posted on November 21, 2015 by winderjssc

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.

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

Beach stone with iron on a Gower peninsula beach in South Wales

Pebbles on the upper shore of a Gower Peninsula beach in South Wales

A beach stone with iron nodules on the Gower Peninsula in South Wales

A beach stone with a centre of iron on the Gower Peninsula in South Wales

Beach stone of banded iron on the Gower Peninsula in South Wales

Pebbles at Whiteford (4)

Posted on August 28, 2015 by winderjssc

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.

Pebbles on the beach near Whiteford Point

Pebbles and seashells on the beach near Whiteford Point

Pebbles, seashells and sand on the beach

Pebbles and seashells on the beach near Whiteford Point with cockle and mussel shells

Pebbles from a sand spit at Whiteford Point

Pebbles and seashells on the beach at Whiteford

Pebbles with a cockle and an oyster shell on the beach near Whiteford Point

View across the sand-covered pebble bar at Whiteford Point

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

Miscellaneous Pebbles with Patterns 2

Posted on January 14, 2014 by winderjssc

Pebble with a natural pattern photographed where it was found on the beach

Rhossili pebbles in a basket

Posted on November 11, 2011 by winderjssc

An assortment of pebbles found on the beach at Rhossili on the Gower Peninsula, showing the significant difference between the appearance of the pebbles when they are wet and when they are dry. This selection of pebbles contains varied rock types but I chose them for display because of their mostly striped markings.

Rhossili pebbles on a plate

Posted on November 7, 2011 by winderjssc

A selection of pebbles from Rhossili Beach: rounded but flattened, with a coarse sandy texture, and in subtle shades of grey, beige and pink, displayed on a sea-green glazed plate. I think these might all be derived from Millstone Grit rock which is part of the Carboniferous Period strata which make up the landward portion of the Gower Peninsula. I am thinking that they could all have been washed around the coastline from their point of origin, or even brought to the tip of the peninsula by the action of the ice sheets that once almost entirely covered Gower.

Pebbles at Rhossili Part 3

Posted on July 3, 2011 by winderjssc

Another selection of the marvellously varied pebbles at Rhossili Beach, Gower.

Revision of a post first published 2 March 2010

Pebbles at Rhossili Part 2

Posted on July 2, 2011 by winderjssc

The pebbles that lie at the base of Rhossili Down in Gower, and extend along Rhossili beach at the foot of the sand dunes known as Llangennith Burrows, are amongst the most colourful and varied that I have ever encountered.

They are mainly quite large but not exactly cobble sized. They range in colour from reds and pinks, orange and yellows, to buffs and greys – many blue-greys. The rocks from which they are composed include limestones, sandstones, grits, and conglomerates. Some come from local strata of the Carboniferous and Devonian periods. Others could possibly originate much further afield and have arrived embedded in massive sheets of ice that once covered most of the Gower Peninsula.

The pebbles range from the smooth and glossy to fine and coarse grained. Occasionally you find ones made up of many smaller chunks and pieces of all types, textures, and hues. The shapes vary from the very irregular to approximately geometric shapes such as circular, spherical, discoid, rectangular, square, and cuboid. Patterns in and on the stones can include stripes, layers, lines, and abstract designs. The pebbles are endlessly interesting and beautiful. These photographs are part of a series showing their immense variability.

The weather was unsettled when I took these pictures; the raindrops of the first shower account for the speckled egg-like appearance of the shots at the top and bottom of the post. After that, the rain came down more steadily and worked in some ways to my advantage by intensifying the colours and imparting a gloss to the surface of the stones.

Revision of a post first published 22 February 2010

Pebbles at Rhossili Part 1

Posted on July 1, 2011 by winderjssc

Looking like lots of pastel-coloured sugared almonds, these pebbles from Rhossili Bay reflect not only the immediate solid geology of the area but also the surface geology relating to former glaciation events.

The pale blue-grey smooth stones are Carboniferous Limestone which outcrops in the two headlands of the bay at Worms Head and Burry Holms. The pink and red relatively coarse-grained stones are derived from the Old Red Devonian Sandstone which forms the basis of Rhossili Down at the head of the bay. Other stones of all sorts, originally from places far away, have been delivered to the location as they melted out of the bottom of an ice sheet or glacier over 10,000 years ago.

Revision of a post first published 26 March 2009

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