Geology walks along the East Devon and Dorset coast

A Walk through Time - Dorset and East Devon, the Jurassic Coast World Heritage Site

England’s first natural World Heritage Site, stretching from Exmouth in East Devon to Old Harry Rocks in Dorset, gives a unique insight into earth science. Its rocks record 185 million years of the Earth’s history through the Triassic, Jurassic and Cretaceous periods – the ‘Middle Ages’ of life on Earth.

Each of the World Heritage Site’s 95 miles offers something new to discover, but here are a few of the more visible features, easily seen from the Coast Path...

The red rocks for which Devon is so well-known are seen in the cliffs between Exmouth and Sidmouth. Their vibrant rusty colour shows they were formed in desert conditions; these prevailed in the Triassic Period, 250-200 million years ago.

The Undercliff National Nature Reserve between Seaton and Lyme Regis is formed from landslips, as sandstones overlie clay and rain reaching the clay layer has made one layer slide over another. On Christmas Eve 1839, an enormous landslide took place at Bindon. A huge piece of land, known locally as Goat Island, moved towards the sea, leaving a deep chasm. Landslides still occur today, making the Undercliff a very wild and special place.

Chesil Beach is over 17 miles (28 km) long and is made up of shingle and pebbles which increase in size towards the east (smugglers apparently knew exactly where they had landed on the beach from the size of the pebbles). There is still debate about how Chesil Beach was formed, although the traditional view is that it has been driven onshore by rising seas levels following the last Ice Age, about 7,000 years ago.

The Isle of Portland’s geology is dramatic. West Weare Cliffs rise majestically from the sea displaying layers of Portland Limestone, Portland Sand and Kimmeridge Clay. On the east of the Island look out for the stunning fossil forest, where doughnut- shaped blocks of limestone indicate where tropical trees were swamped some 135 million years ago. Natural fractures or 'gullies', as they are known locally, criss-cross the Island.

The perfect horseshoe bay of Lulworth Cove was developed where a stream breached the limestone, allowing the sea to enter and hollow out the softer clays behind the limestone barrier. The back wall of the bay is formed by more resistant chalk. Beside Lulworth another bay is forming at Stair Hole. Here you will see the famous Lulworth Crumple - a complex fold formed by major earth movements at the time when the Alps were formed.

The sheer cliffs of the Purbeck coast are formed by Portland Stone and Purbeck Limestone, rocks that are well-displayed in the old cliff quarry workings at Seacombe, Winspit and Dancing Ledge. The area is also famous for the tracks of dinosaurs such as Megalosaurus and Iguanodon, and for an internationally important fossil record of mammal evolution.