The Shore Below the New Sea Wall (Part 2)

The rock ledges below the new sea wall at Church Cliffs in Lyme Regis, Dorset, are the upper strata of the Blue Lias limestone. The natural limestone ledges and the smooth artificial substrate of the concrete sea wall,  provide a home for numerous seashore creatures like limpets, winkles, and top shells as well as many commonly attached red, green and brown seaweeds, and encrusting calcareous algae (pink Lithamnion). The brown substance sticking to a lot of limpet shells is also an encrusting seaweed (probably Brown Limpet Paint Ralfsia verrucosa).

Multitudes of small holes penetrating the rocks are the often-occupied burrows of small marine polychaete worms like the Polydora species. Occasional drifts of sandy ripples coating the stone are punctured by largish round holes where bivalved burrowing piddocks living in the rocks below have squirted jets of water from their exhalent siphons and cleared the sand away.

It is interesting to see that the seashore life is equally at home on the old concrete footings from the defunct breakwaters as it is on the limestone.

The Shore Below the New Sea Wall (Part 1)

The shore beneath the new sea wall in Lyme Regis looks very different now the old breakwaters or groynes have been removed. You can still see the linear concrete footings of the old wood and iron structures but most of the pebbles and cobbles that used to accumulate between the walls are now absent (at least for the moment). A bare rock pavement is revealed, comprising a series of steps representing the strata and colonised by seaweeds. Rippled sand sometimes deposits in the valleys between the rock ledges.

Views at Osmington Bay

View with red and green seaweeds at Osmington Bay, Dorset, UK, looking west - part of the Jurassic Coast 

Probably not amongst the most familiar of Dorset beaches, nor the easiest to access, Osmington Bay is nonetheless full of interest and well worth the visit. The best way to the beach is to drive to the Smugglers Inn at Osmington Mills and park on the cliff top. You can just about clamber down to the shore from the car park – but it is safer to skirt around the pub using the South West Coastal Footpath and detour over the stile to descend the proper path and steps to the seashore.

The large boulders and cobbles that strew the shore mean that this beach is most suited to the agile, especially when the weather is poor and wet. It can be very slippery and progress tiring. However, every few hundred metres brings something new to look at – the aspect, the rocks, the structures, the seaweeds.

The picture above shows the view looking westwards towards Weymouth. The boulders at the water’s edge are covered in brightly coloured green and red algae that has washed ashore.

View at Osmington Bay, Dorset, UK, looking west from Frenchman's Ledge - part of the Jurassic Coast (2) 

This picture was taken looking west from Frenchman’s Ledge – a rocky platform projecting out into deeper water. The name arises from a local story that smugglers in times gone by would land their boats here at night to off-load contraband goods brought over the Channel from France.

View of Osmington Bay, Dorset, UK, looking west towards Weymouth - part of the Jurassic Coast (3) 

This picture shows a view to the west on Osmington Beach showing the large cobbles and boulders covering the shore. In the middle distance is a rock platform called Hannah’s Ledge.

View from the clifftop at Osmington Bay, Dorset, UK, across the Ledges to Portland - part of the Jurassic Coast (4)

This is the view on a good day, looking down from the Smugglers Inn car park on the cliff top showing the rocky ledges extending out from the Osmington Bay shore below, and across the water to Portland on the horizon.

View of a cloud burst over Weymouth from the cliff top at Osmington Bay, Dorset, UK, part of the Jurassic Coast (5)

This is a similar view just as a storm was about to hit Osmington. The ominous overhead clouds had just burst right over Weymouth and Wyke Regis. You can see the rain cascading down. A shadow is cast over half the surface of the sea which has a strange luminous green colour. Portland remained fine for the moment but we did not escape a soaking ourselves.

View of Osmington Bay, Dorset, UK, with iron-stained rocks, looking east towards Bran Point and Ringstead Bay - part of the Jurassic Coast (6) 

One of the features that attracts me the most about Osmington Bay is the amazing colourful patterns on the rocks – like the one on the boulder in the foreground of this picture. I will be talking more about the rock patterns in subsequent posts.

View at Osmington Bay, Dorset, UK, with disused iron winch, looking east towards Black Head Ledges - part of the Jurassic Coast (7) 

Despite the current difficulty in getting down to the beach from the car park, it is obvious from the existence of a slipway that this location is, or has been in the recent past, used by fishermen.  The rapid erosion of the cliff may mean that this is not such a feasible activity today. Old winches for hauling the boats up the shore now lie rusted and useless – like the one now lying on the shore in the above photograph. The view is looking west across the bay towards Black Head Ledges.

The last view is looking east along the Osmington shore towards the east, Bran Point, and Ringstead Bay beyond. The most noticeable features in this shot are the large rounded brown boulders in the foreground. These are extremely interesting geological phenomena.

View at Osmington Bay, Dorset, UK, with rounded boulders, looking east towards Bran Point and Ringstead Bay (8) 

Revision of a post first published 12 June 2009


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Rock pavement at Kimmeridge Bay

P1050977aBlog1 Yellow rock pavement at Kimmeridge Bay, Dorset, UK on the Jurassic Coast World Heritage Site 

Rock platforms, pavements or ledges are a most fascinating feature of the beach at Kimmeridge Bay in Dorset. The cliffs are made up of alternating layers of various mudstones and bituminous shales making up the Kimmeridge Clay sequence. The ledges are seaward projections of the harder limestone rock layers that arise from the base of the cliffs. They are dolomitic limestone which is basically dark grey but when it contains a higher proportions of iron it is yellowy.

The ledges and platforms are covered with cracks and crevices forming interesting geometric shapes. Viewed from above, a larger pattern of shapes, termed megapolygons, is visible. I do not fully understand the processes that underlie the creation of these natural designs. I think the tremendous pressure of what was once a kilometre deep layer of sedimenatry rocks above this stratum, and crystallisation within the sediments of this particular layer, may have been contributary factors.

Whatever the cause of them, the patterns are intriguing; and I will show more photographs of them in later Posts. The smooth flat surfaces and the crevices of the ledges and pavements provide substrates on which seashore animals and plants can settle and shelter – thus contributing to the fantastic array of wildlife that occurs at Kimmeridge in this marine wildlife reserve.

For more information about the geology of Kimmeridge Bay see the most excellent academic guide written by Ian West of the National Oceanography Centre in Southampton University.

For more information about Kimmeridge Bay and its wildlife you can refer to the Purbeck Marine Wildlife Reserve Web Site.

P1060201aBlog2 Grey rock pavement on the shore at Kimmeridge Bay, Dorset, UK - part of the Jurassic Coast World Heritage Site 


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