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Geology And Palaentology

Contributed by Dr Martin Munt, Curator and General Manager – Dinosaur Isle Museum

Whether you chose east, west or south from Yarmouth you can soon be exploring one of Britain’s richest fossil localities, even where dinosaurs walked 125 million years ago.

If you decide to go east towards Hamstead and Bouldnor, or indeed just walk west along the beach from Yarmouth, you can find the bones and teeth of alligators, turtles and mammals that lived here 35 million years ago. The bones are black, and look for that honey-comb structure that was once the marrow. Turtle shell is very common and is flat and may have wavy patterns on one side.

West opens up a range of sites between Fort Victoria, through Colwell Bay, Totland Bay and ultimately to Alum Bay. The soft cliffs contain layers of fossil shells, which can be extracted with a knife. You will also see hard white limestones full of fossil pond snails.

At Alum Bay the rocks are vertical, and you can see the world-famous coloured sands. Also, at Alum Bay you will see the magnificent chalk cliffs that end at The Needles. The chalk dates to the late Cretaceous period, about 85 million years ago. Search amongst the pebbles on the beach for sea urchins preserved in flint.

A journey south to Compton Bay is a must for the dinosaur enthusiast. 125-million-year-old dinosaur footprint casts can be seen on the beach in Compton and Brook bays, with the biggest concentration at Hanover Point. If you are lucky enough you might find your very own piece of dinosaur bone amongst the pebbles.

Geological Heritage

Yarmouth is a great place to travel out off to explore the Isle of Wight’s rich geological heritage, in fact you can see most of the Island’s different rock types within just a few miles, including the oldest and youngest rocks which form the Island.

The Cretaceous 128-85 million years ago (locally) and The Wealden Group (128-121 million years ago)

Beginning with the oldest rocks which date to the Early Cretaceous, the Wealden is the richest source of dinosaur remains in Europe. You can access these rocks between Compton Bay and Atherfield on the west coast, or at Yaverland on the east coast. Layers of black fossil wood within these rocks are the main source of dinosaur bones. Sandstone and colourful mudstone layers have the footprints preserved in them. Laid down by rivers, in ponds and a flooded landscape with pine trees and tree ferns, the seasonal hot dry then wet winter climate supported an ecosystem of almost 40 different dinosaurs, along with pterosaurs, crocodiles and invertebrates.

The Lower Greensand (121-113 million years ago)

Around 121 million years ago the sea level begun to rise and the land which was home to the dinosaurs was covered by a warm shallow sea. The rock layers which record that sea can be seen at Atherfield, Sandown Bay and Compton Bay. Layers within these rocks contain a vast array of sea creatures such as clams, corals, lobsters and ammonites. Some of these ammonites are almost a metre in diameter.

The Upper Greensand and Gault Clay (113 – 100 million years ago)

As the sea deepened, the whole of southern England became flooded by the sea. Similar types of fossils are found in these rocks to the Lower Greensand. Individual chambers from ammonite shells are quite common on the beaches between Shanklin and Bonchurch, these are called cat’s paws, sometimes whole ammonites can also be found. Less commonly found are fish, shark’s teeth marine reptile bones.

The Chalk

(100-85 million years ago)

The Chalk is the youngest part of the Cretaceous in England, and on the Island stretches from Culver Cliff in the east to The Needles in the west. It forms the downs that divide the Island and the high plateau above Ventnor. The oldest parts of the Chalk are rich in ammonites, shark’s teeth and clams. A visit to St Catherine’s Point, or the beaches around Ventnor should provide a rich haul of finds. The younger part of the Chalk, the White Chalk forms the magnificent cliffs between Compton Bay and Alum Bay. These cliffs are best avoided, but where safe you can find sea urchins, sponges and the bullet-like belemnites, an extinct form of squid.

Flint sea urchins - Photo by Dinosaur Isle

Flint sea urchins – Photo by Dinosaur Isle

The Paleogene (61-33 million years ago locally) and The Reading, London Clay, Bracklesham and Barton groups (61-37 million years ago)

The Eocene rocks are seen at Alum Bay and Whitecliff Bay, where they form the vertically bedded cliffs. Rich in fossil shells and shark’s teeth, they were laid down over the eroded top of the Chalk by warm shallow seas and shallow lagoons and estuaries at different times. The sea levels were beginning to drop as the world cooled at the end of the Cretaceous, and these rocks record a changing world.

Turtle and tortoise shell - Dinosaur Isle

Turtle and tortoise shell – Photo by Dinosaur Isle

The Solent Group

(37-33 million years ago)

The youngest rocks on the Island we call the Solent Group; these range in date from the end of the Eocene into the Oligocene, and the rocks are unique to the Island and parts of the New Forest. With many layers of shells that mostly record shallow lagoons and lakes, fossils are very easy to find. Amongst these are the teeth and bones of mammals, turtles and alligators. The Solent Group forms the cliffs between Headon Hill right round the north coast to Bembridge. Some sites such as Gurnard are world famous for beautifully preserved insect fossils.

The Quaternary – An Island Is Formed

As the Solent Group was being formed, southern England was being uplifted and the rocks folded; this is when the rocks at Alum Bay were pushed up to become vertical. The Ice Age began just over two million years ago, and since then the Island has at times been joined to the mainland or separated by the Solent. In places such as Newtown and Bembridge Foreland we can see layers of grave and clay laid down 125,000 years ago. At Newtown, the clays contain the bones of bison, elephant and hippo. Gravel deposits around the Island contain teeth of mammoth, and rarely stone tools made by our ancestors.