Fossil hunting and geology at Compton Bay and Downs

Foot casts from a giant plant-eating dinosaurs have fallen out of a hard layer of siltstone in the crumbling cliffs. This area may once have been a dinosaur migration route, with herds of dinosaurs following the muddy banks of rivers, looking for plants and water. Their footprints have been filled in with silt and preserved. 

It's rarer to find foot casts of meat-eating dinosaurs on the beach but they’re always worth looking out for. These dinosaurs were generally smaller than the plant eaters and tended to have narrower, more pointed toes. 

You may be lucky enough to find a small piece of dinosaur bone on the beach. Look out for the honeycomb structure. Don’t confuse bone with lignite (fossilised wood). It leaves a black mark when scraped on rock but fossilised dinosaur bone doesn’t.

One of the commonest fossils found on the beach, lignite is a piece of wood that’s been fossilised. It looks like impure coal and is black, owing to the way it’s been mineralised. Sometimes you can see the grain of the wood in the fossil or even impressions of the bark.  

Near Hanover Point there’s a layer of grey silty sandstone that has a brown crusty-looking texture on its upper surface. This top layer was once soil and that too has now been fossilised. 

Mud cracks show where a freshwater lake has dried out and flooded again, with silt filling in the cracks. It looks like modern-day crazy paving. You can find these on the underside of some of the shelly limestone slabs. 

There’s a layer of limestone in which large numbers of freshwater bivalve shells called Filosina have been preserved. The layer can be quite thin, and the fragments look like uneven, discarded paving slabs. 

You may find large fossil oyster shells which come from a band of grey and green clay and sand. They show that the environment has become marine, as opposed to the freshwater deposits that gave rise to the dinosaur and wood remains. 

Ammonite fossil fragments lie in the Grey Chalk, which is older than the White Chalk, but it would have been part of the same warm tropical sea. There are also bivalve shell fossils from this time. 

Fossilised sea urchins have been preserved in flint. When they were alive, they would have scavenged for food on the sea floor. 

If you spot a flint that’s fallen from the chalk cliffs, the chances are high that it was originally a sponge. Most flint are the fossilised remains of sponges that grew on the floor of the tropical sea. Some flints even show the actual shapes of their original sponges. 

The layers of gravel at the top of Compton cliffs were deposited by a river that meandered towards Freshwater Bay. Occasionally, pieces of semi-fossilised wood can be seen. They would have fallen into the riverbed at the same time. 

You can sometimes find semi-fossilised hazelnuts (known locally as ‘Noah’s nuts’) on the beach near the steps at Hanover Point. These come from the same layer of gravel as the semi-fossilised wood and would have been dropped into the river around the same time.  

The tug Carbon was being towed from Portland to Southampton for salvage when the towing line broke whilst off the Needles in 1947. The ship drifted into Compton Bay and went aground on the rocks. 

It was decided she wasn't worth recovering and she has remained a familiar landmark, slowly rusting away so there’s less to see each year. 

Atlantic storms sweeping into the English Channel mean that the southwest coastline of the Isle of Wight is eroding fast. Car parks and roads will not stop this natural process – the National Trust car park at Hanover Point loses parking bays at regular intervals.  

Along the beach at Compton you may find parts of the car park surface, which sometimes get mistaken for rare dinosaur bones.