CLICK ON THE IMAGE FOR A SHORT VIDEO OF WAVES AND REFLECTION PATTERNS
Waves washing onto a seashore rock ledge, with dynamic patterns of reflected light each time the water retreats.
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Waves breaking on the rock ledge at Winspit, Dorset, UK, on the Jurassic Coast where stone was quarried from the cliffs in times gone by and loaded onto boats.
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The waves breaking on the man-made rock ledge at Winspit, Dorset, UK on the Jurassic Coast, where stone was quarried long ago and loaded straight onto boats.
CLICK ON THE IMAGE BELOW FOR A SHORT VIDEO OF THE WAVES
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This really is a square rock pool. It is one of several to be found on the rock ledge at the foot of the cliffs at Winspit in Dorset. These square pools are scattered amongst the more usual and variously shaped pools on the rock ledge. All the pools are lined with a continuous coating of pink or bleached white calcareous algae. They are fringed with red Coral Weed or green Gutweed and provide a home to an assortment of gastropod molluscs and small fish.
However, the square rock pools are man-made and provide evidence for the industrial history of the area. This is the site of a former quarry. The workings are mostly on the cliff top where you can still explore, with care, the cave like excavations. Large blocks of stone were at one time painstakingly hewn from the strata. The rock was too heavy to cart up the hill to the village. So cranes were constructed from old ships timbers and driftwood in order to lower the stone from the cliff top to the ‘beach’ below. Another set of cranes was built on the rock platform at the water’s edge to lower the stone into boats. The square pits were carved to hold the base of the main wooden post for these cranes.
Carts were used for transferring the stone from the foot of the cliff to the edge of the ledge. As you might imagine, this could be a bit tricky on a wet and slimy surface. In fact, this operation could only be undertaken in the summer months when conditions were more favourable. The carts were pulled by two men. To stop the carts slipping, over-turning, or going in the wrong direction and into the sea with the hard-earned cargo, two parallel ruts were carved in the rock to accommodate the wheels – a bit like tramlines. Two sets of these cart ruts can still be clearly seen.
Revision of a post first published 15 November 2009
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Trace fossils are geological records of biological activity. The rocks at Winspit in Dorset have preserved evidence of the burrowing habits of invertebrate animals that once lived in the soft wet sediments on the seabed and seashore of shallow seas over 135 million years ago in the Upper Jurassic period.
These trace fossils include burrows and tunnels made by crabs and worms. In some instances, the holes made by the creatures remain visible – as pictured in the first three photographs below. They look remarkably similar to the holes made by boring bivalved molluscs and by mud-tube dwelling marine polychaetes that occur in present day calcareous stones and mollusc shells (see the earlier posts on these subjects). As I am not a palaeontologist, I concede that this may not actually be a parallel causation – just a coincidence.
In most of the examples illustrated by the photographs below, the spaces enclosed by the burrows have been infilled by other sediments so that instead of the original hollow tubes and tunnels remaining in the hardened rock, the burrows have become roughly cylindrical solids. The infill substance seems to be harder than the matrix surrounding it. This means that the softer rock has weathered more readily and the burrows stand out like cords.
A pile of large angular boulders, between one and two metres across, rests on the rocky ledge at the foot of the cliffs where the valley meets the sea at Winspit. On the flat surfaces of some of the rocks are intricate patterns made up of horizontally branching networks of solid tubes about a centimetres or so in diameter. These are similar to the burrows made by decapod crustaceans (crabs) called Thalassinoides.
Large fossilised remains are found in these strata as well as the trace fossils. One of the best known, because of its large size, is the ammonite Titanites giganteus as shown in the picture above. It is about 40 centimetres in diameter. Although well embedded in the massive boulder, and a feature of the location for as long as anyone remembers, someone has recently tried unsuccessfully to hack it out of the rock. It is a shame because it has left the wonderful fossil damaged and defaced.
Some of the burrows, particularly the larger ones that may have been made by crabs, seem from these trace fossils to have passed through a series of layers in the sediments. Sediments from different layers are mixed up, and older sediments brought to the surface and deposited above more recent ones, as animals excavate their tunnels. This process is called bioturbation. Geologists, palaeontologists, and archaeologists are all aware of the implications of bioturbation for the interpretation of results from their research and excavations.
Another name for trace fossil is ichnofossil. To read some more about ichnofossils click here.
Revision of a post first published 9 December 2009
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Sparkling waves breaking on the rock ledge of the shore at Winspit, Dorset, UK, on the Jurassic Coast – site of ancient quarrying activities.
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If you get on your hands and knees to peer closely at the acorn barnacles high up on rocky shores, especially in the splash zone, you may be surprised to see tiny gastropod molluscs on them, between them, and even sheltering inside their empty cases. Some of these molluscs look like smooth, dark grey grape pips. They are Small Periwinkles, Melarhaphe neritoides Linnaeus, formerly known as Littorina neritoides.
Small Periwinkle shells have a flat-sided spire and pointed apex. The main shell body whorl is black or brown but the colour is variable and light-hued specimens do occur. The surface of the shell is generally smooth but the body whorl may have spiral banding or vertical stripes. The whole shell measures no more than 9mm high by 7mm across and many are a lot smaller. These seashore creatures feed on detritus and black lichen. Black lichen can grow in very small patches on barnacle shells or as more extensive areas on the rocks. At Winspit in Dorset where these photographs were taken, the appearance of the barnacle shells has been altered by the presence of endo-lithic lichens so that they have many pits and lace-like sculpturings. The pits are the place where the fungus part of the lichen produces spores. It is possible to see these as small black dots in some of the pits.
You can read more about this endolithic lichen and pitted barnacle shells in an earlier post: Pitted barnacle shells at Bran Point.
Also present in these photographs is the larger Rough Periwinkle – Littorina saxatilis (Olivi) - which tends to be yellow and is covered with sharp spiral ridges. You can read more about Rough Periwinkles in an earlier post: Rough Periwinkles at Kimmeridge Bay.
Revision of a post first published 17 December 2009
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Small rock pools are scattered across the rock ledge at Winspit. Some are shallow and others are deep. Some are on the general surface and others are embedded in rock clefts. Most are rounded in outline but a few are differently shaped. Some of the pools shown here seem almost like the shape of an eye or a mouth.
The colours and patterns made by the various seashore creatures and seaweeds found in and around the rockpools make attractive natural arrangements and designs. The pools and their inhabitants are very decorative features on the seashore even if you do not know what everything is called.
These are really remarkable rockpools and unlike any that I have seen before. The general surface of the rock in this location is covered with an almost continuous coating of encrusting calcareous algae. This is Lithamnion, usually pink or purplish, but in many areas here it is bleached-out and white. Patches of smooth black encrusting lichen, and microscopic green algae, are interspersed with the Lithamnion to form an irregular background patchwork of colour.
The purple-tipped, grey-green tentacles of Snakelocks Anemones clustered en masse in some pools. Tufts of filamentous red seaweeds were dotted all over the place and seemed to have a penchant for settling like plumed feathers on the conical shells of living limpets. The arcticulated, calcareous, pink and white branches of Coral Weed created tufts in pools and extensive carpets on the flat rock surfaces.
Yellow Rough Periwinkles grazed the red seaweeds. The unusual green Velvet Horn seaweed was growing in some pools. A few pools had nothing but pebbles swirling round and around at the bottom – preventing any organisms from settling. The red Beadlet Anemones were such a dark colour they looked almost black. Altogether this small area of shoreline with its numerous rockpools is a most unusual-looking place.
Another set of odd-shaped rockpools is described in Cart tracks and square rockpools at Winspit ………and for more details about the weeds and invertebrate seashore creatures mentioned above, you can use the SEARCH BOX on the top right-hand side of the blog’s home page, or the INDEX OF CATEGORIES, to locateother postings on the subjects.
Revision of a post first published 8 December 2009
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Masses of the olive-green seaweed, commonly known as Thongweed, are a frequent sight on the seashores along the Jurassic Coast. The Latin name for this type of brown alga is Himanthalia elongata (Linnaeus) Gray.
These tangled stringy heaps represent just a part of the whole seaweed. They are the seasonally produced free-floating reproductive parts. They are cast off periodically from the longer-lived, fixed, part of this member of the group Phaeophycae. The perennial part is permanently fixed to the substrate in deep inter-tidal rock pools low on the shore or off-shore. It is not so frequently observed or recognised as the straps.
The perennial part of the alga is surprisingly small given that the fertile straps can be more than two metres long. The plant starts off as a small club-shaped structure a few millimetres wide and attached by a short stalk to the rock. The swollen tip gradually enlarges and flattens out into a roughly circular, flattened disc about 30 mm wide with a dimpled or concave surface – resembling a button or mushroom.
Photographs of this structure are shown above and below. They were found in pools on the rock platform at Winspit - near to extreme low tide – growing on Pink Paint (a calcareous encrusting alga) amongst Coral Weed and other filamentous red seaweeds. Two small bumps in the middle of the cupped surface indicate where the reproductive straps were once attached.
The long straps change from their original light olive green colour to a more yellowish shade with brown spots when they are ripe and ready to shed the reproductive products into the sea. This is shown in the photographs below.
Thongweed has also been described in earlier posts. These include:
Seaweed-inspired fabric design
Revision of a post previously published 27 May 2010
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