A Fossil hunt at Atherfield – 28th September
On a beautiful, warm and sunny late September afternoon I can’t imagine enjoying anything half as much as simply strolling along a sandy beach hunting for fossils. And some twenty-five of our members must have thought so too, for they accepted my invitation to come along. Paul Newton and Steve Hutt, from the Geological Society of the Isle of Wight, kindly offered to take us on a guided walk, and they brought with them some fellow enthusiasts.
We met on the Military Road near Atherfield Bay Holiday Camp and walked along Shepherd’s Chine to the beach. Looking westward, Paul and Steve described the various geological formations of the coastal landscape, from the south-westerly tip of the island at the Needles to where we were standing. The very white Upper Chalk cliffs west of Freshwater Bay are full of flint. They are almost vertical, owing to a collision between Africa and Europe, and earlier tectonic plate movements, which squeezed the land and forced it upwards. Chalk is a marine rock. Middle and Lower Chalk, which is full of marcasite and iron, extends into Compton Bay, where the base of the Lower Chalk can be seen. Beyond this, sandwiched between the Upper Greensand and the Lower Greensand there is Gault (or ‘Blue Slipper’) Clay. All the rocks within our view, from the Needles to St Catherine’s Point, are of Cretaceous age. On the island the rocks get increasingly younger as you travel northward. The Wealden beds, from Compton Bay to Atherfield Point, contain the skeletons of terrestrial dinosaurs which are a hundred and thirty million years old. There are also trace fossils of dinosaur footprints which have fallen onto the beach. We turned eastward, where the mudstones of the Shepherd’s Chine Member form the base of the cliffs as far as Atherfield Point. Here we found thin slabs of limestone on the beach. These are packed with shell debris: disarticulated valves of the brackish water bivalve Filosina gregaria. Turning them over, we discovered many small U-shaped Diplocraterion burrows. These limestones may have been formed by storms sweeping across a shallow lagoon.
In the Perna Bed (Greensand), at the base of the Atherfield Clay Formation, you can find bivalves (two shells hinged together, such as oysters), gastropods (snails), brachiopods (similar to bivalves, and which attach themselves to rocks), corals and serpulid worm tubes. We found various kinds of fossilised oyster shells, including a flat type and the large oyster Aetostreon. Oysters build up many layers of shell for defence against rough seas and predators. There were also many trace fossils in the rocks strewn about the beach. These are the burrows and trails made by various sea creatures moving through the mud on this shallow marine shelf.
At Atherfield Point there is a hard ledge of Perna Bed forming a long reef at low tide where you can find bivalves and a small bun coral the size of a golfball. From here we could see the whole of Chale Bay, as far as St Catherine’s Point. Continuing eastward, we came across soft, grey-brown clay containing fossilised lobsters. These are identified as blue or pinkish-brown protuberances.
The highlight of the walk for me was discovering the crackers, huge doorknob shapes dotted along two horizontal strata on the lower cliff-face. Some of the nodules have soft cores containing beautifully preserved ammonites, bivalves, molluscs, gastropods, crustaceans, and echinoderms (such as sea urchins, the skeleton being composed of six-sided plates).
The Back of the Wight, or south coast of the island, is a good area for fossil hunting because its cliffs are constantly falling, but this is also a hazard. Another is being cut off by the tide. You need to time your trip to coincide with a falling tide, giving you some hours to explore before the tide reclaims the beach. Here you can easily lose track of time, and so it is a good way to unwind from the hectic demands of twenty-first century living.
The coastal scenery from Atherfield to St Catherine’s Point is dramatic, untamed. Virtually sheer cliffs rise like impenetrable fortresses, dominating the landscape and dwarfing any humans on the beach. Only the most adaptable plants still cling to these crumbling walls. Wind and rainwater have carved the Upper Greensand at the top into fantastic shapes: pinnacles and turrets. Streams of brightly coloured minerals: red and yellow, flow from the base of the cliff, staining the rock. It only takes a little imagination to transport yourself back some two hundred million years to an age, long before Man evolved, when ammonites flourished here.