Rock textures at Saundersfoot

Natural rock textures and patterns

The natural textures and patterns in the cliff rock strata near Coppet Hall at Saundersfoot, South Pembrokeshire, Wales, really caught my eye on a first visit to the location. The stratigraphy is intriguing and complicated – and I have yet to work out exactly what I am looking at. I need a detailed geological map of the area and access to published papers for that. However, I think it fairly safe to say that they belong to the Upper Carboniferous Period, probably the Namurian, also known as the Lower Coal Measures, comprised of sandstone and mudstone layers, with coal seams and layers of iron nodules. I’ll check it all out when I can. High quality anthracite coal was open-cast mined not far away, and there used to be a local iron smelting industry.

My key guide to the geology of Gower and South Wales (George 2008) only describes in detail the geology of the stretch of beach immediately north of this place, and immediately south of it, leaving me a bit stumped as to an explanation for its peculiarities. I am definitely going back to this coastline to spend some quality time exploring the intricacies of its geological history, and photographing some of its marvellous natural abstract compositions.

REFERENCE

George, G. T. 2008, The Geology of South Wales: A Field Guide, gareth@geoserv.co.uk, 978-0-9559371-0-1.

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

Porthmeor Rocks 2

These rocks are seen on the west side of The Island or St Ives Head in Cornwall, England. They form outcrops on the west side of Porthmeor Beach. I was fascinated by the sheer complexity of the colours, patterns and textures. As far as I can make out they belong to an un-named igneous intrusion (matagabbro or metamicrogabbro) composed of silica-poor magma which was later altered by low-grade metamorphism in the Devonian period between 359 and 416 million years ago.

The rock looks very different from that nearby which was featured in an earlier post. I was particularly drawn some outcrops which had an almost dark navy blue smooth surface but the majority of the rock surfaces were blue-grey and dirty yellow shades – some with smoother almost layered textures and others textured like lumpy porridge. The patterns were complex but included ancient splits and cracks that had been infilled with other materials of contrasting colours, giving paler or darker straight lines and angled cross lines – not to mention all the complicated later fracture patterns. There seemed to be large inclusions of other rock types too; this often occurs in granites. It is incredible that rocks of the same basic type can vary so much in their appearance within a few metres.

Thames flood-tide current 3

Video

As the tide flows upstream near high water on the River Thames in London, the down-flowing river is maximally conflicted, resulting in interesting movement and patterns of reflected light.

Click on the pictures below for a more detailed version.

Natural abstract water patterns

Natural abstract water patterns

Natural abstract water patterns

Natural abstract water patterns

Natural abstract water patterns

 

Rocks at Porthmeor Beach, St Ives

The rocks in Cornwall are certainly different from any that I’ve seen before. Generally speaking, they are mostly igneous and metamorphic in type. Often the igneous rocks themselves have been metamorphosed. The rocks shown here were seen on the beach at Porthmeor and adjacent to The Island at St Ives. They lie below a thick layer of rusty-coloured superficial deposit of glacial till. I am not absolutely certain what the bedrock is. There are a number of rock types described by the British Geological Survey in their Geology of Britain Viewer in close proximity to each other, and it is rather difficult for an amateur to decide which is which. However, this particular outcrop reminds me of basalt which I saw on the shoreline of Grand Manan in the Bay of Fundy in Canada. So, I am going to suggest that it is an un-named mafic igneous rock formed of silica-poor magma that intruded into the earth’s crust in the Devonian Period between 359 and 416 million years ago. When the magma cooled, it formed an intrusion of fine to medium crystalline rock, often as basaltic dykes and sills.

On the other hand, I could be wrong, and it might be an un-named igneous intrusion of Metagabbro and Metamicrogabbro; or even Mylor Slate Formation with Hornfelsed Slate and Hornfelsed Siltstone.