Yorkshire's Jurassic Park

Ammonites can be found quite easily on the beach at Port Mulgrave © Gareth Wilson

Ammonites can be found quite easily on the beach at Port Mulgrave

On the Yorkshire coast rocks from the Jurassic period (dating back 150-200 million years ago) are exposed for all to see, in a series of spectacular cliffs and bays. This continuous exposure of rock has made the Yorkshire coast popular with geologists for generations. It was here, in the early days of geology, that many secrets of the earth’s history were discovered.

Rocks on the Yorkshire coast tend to become younger as we go from north to south down the coast.

The Lower Jurassic and creatures from the deep

Around 200 million years ago, at the beginning of the period we now call the Jurassic, this region was covered by sea. An extensive ocean covered the whole of Europe and was home to a great variety of marine life. Many of these creatures are preserved in the mudstones and thin limestones that were deposited on the ocean floor. Ammonites are common and occasionally the bones of one of the great marine reptiles that swam in these seas are found. 

You can hunt for fossils in Lower Jurassic rocks between Saltburn-by-the-Sea and Staithes.

The Middle Jurassic and dinosaur footprints

The ocean receded from this area by the time of the Middle Jurassic, around 170 million years ago. The region became a coastal area with deltas, scrub and forest. The sandstones and mudstones formed in this period contain plant remains and the traces of land animals as well as marine fossils. Dinosaurs left their mark here too in the form of footprints and the occasional bone. 

Fossils from the Middle Jurassic can be found at Port Mulgrave and Runswick Bay.

The Upper Jurassic and tropical seas

The sea invaded this area again in the Upper Jurassic period, around 150 million years ago. This was a warm, shallow sea. Most of the fossils from this time are of animals living on the sea bed preserved in gritstones, limestones and clays.

From Scarborough a series of faults pushes rocks of the Middle and Upper Jurassic next to each other creating headlands and bays such as those at Filey.

The changing coast

The landscape of the Yorkshire Coast has been shaped over millions of years. Some of the processes are extremely slow – take the formation of rock from sand deposited at the bottom of the sea for example. It takes time.

However, some processes are surprisingly fast. The rocks of the coast bear evidence of landslips, underwater slumps and other changes that happened millions of years ago but took only a matter of days to have their effect. 

These changes have not stopped – the sea is still battering away the coastline while sand is being brought by rain and rivers and laid on the sea bed. Geology goes on working.