Bivalve shell

Why are fossils from Lyme Regis in Wareham Museum?

The answer is that we wanted to make the connection between the oil under Poole Harbour (the Wytch Farm oilfield), and the rocks from which the oil originated. The oil comes from organic material trapped in rock. These rocks formed on a stagnant sea floor where the organic material, mostly plankton, rained down onto the sea bed and became buried in the sediment.

At Charmouth and Lyme Regis, you can see the layer of dark clay rocks that the oil comes from, but you can’t see this rock at the other end of the Jurassic Coast. This is because the coast dips to the east, so much so that in Purbeck and Poole Harbour, the rocks are buried underground. In fact, they are deep enough for heat and pressure to ‘cook’ the organic material into oil and gas. The petroleum industry calls these places ‘kitchens’. The Charmouth coast doesn’t produce oil because the rocks are not buried deep enough, but around the world there are thousands of places where underground organic-rich rocks do form oil – and our entire economy is based on it. Who says geology is dull or unimportant!


These impressive bivalve shells came from Lyme Regis. Find out more about bivalves on the molluscs pages.

Common name

Bivalve shell

Scientific name

Lima (Plagiostoma) giganteum


Molluscs > Bivalves


Blue Lias

Time period

Lower Jurassic


200 million years

Where found

Pinhay Bay, Lyme Regis

Found by

Richard Edmonds


Wareham Museum

Accession number

WARE 00001