Lulworth to Durdle Door

Lulworth Cove is an almost perfectly circular bay in the rolling line of cliffs that form Dorset's southern coast. Its pristine condition and geological importance earned it World Heritage status in 2002.The cove provides a secure anchorage for small fishing boats and pleasure craft, and a sun-trap of safe water for summer bathers. The cliffs around the eastern side of the bay are crumbly soft and brightly coloured in some places, while around the opposite arm the rock appears to have been folded and shoved aside by an unseen hand. The geology is intriguing and a visit to the Heritage Centre will help you to sort it out.

The oldest layer, easily identified here, is the gleaming white Portland stone. This attractive stone was much employed by Christopher Wren in his rebuilding of London. It is a fine-grained oolite, around 140 million years old. It consists of tightly compressed, fossilised shells - the flat-coiled ones are ammonites. Occasional giant ammonites, called titanites, may be seen incorporated into house walls across Purbeck. Like the rock of Bat's Head, it may contain speckled bands of flinty chert. Above this is a layer of Purbeck marble, a limestone rich in the fossils of vertebrates. This is where dinosaur, fish and reptile fossils are usually found. The soft layer above this consists of Wealden beds, a belt of colourful clays, silts and sands, that are unstable and prone to landslips when exposed.

Crumbly, white chalk overlays the Wealden beds. The chalk consists of the remains of microscopic sea creatures and shells deposited over a long period of time when a deep sea covered much of Dorset, some 75 million years ago. This is the chalk that underlies Dorset's famous downland and is seen in the exposed soft, eroded cliffs at White Nothe. Hard nodules and bands of flint appear in the chalk - it's a purer type of chert - and in its gravel beach form it protects long stretches of this fragile coast.

The laying down of chalk marks the end of the Cretaceous period in geology. After this the blanket of chalk was uplifted, folded and subjected to erosion by the slow, inexorable movement of tectonic plates. The Dorset coast was exposed to some of its most extreme pressure between 24 and 1½ million years ago, resulting in folding, crumpling and sometimes overturning of strata. You can see this in the vertical strata on rocks around Durdle Door and Stair Hole.

Where to eat and drink

In Lulworth the Heritage Centre café includes family meals and baguettes. Just down the hill, the Lulworth Cove Hotel is open all year and serves a multitude of fresh, locally caught fish.

What to look for

Don't miss the baby-blue painted Dolls House on the way down to the harbour in Lulworth Cove. It's a fisherman's cottage dating from 1861. You may find it difficult to believe that 11 children were raised in this tiny house. Contrast its cramped simplicity with the dwelling opposite, with diamond-pane windows and a cosy thatched roof, built in a decorative style known as 'cottage orné'.

While you're there

At nearby East Lulworth is Lulworth Castle Park. The castle itself, a 17th-century hunting lodge built four-square with pepperpot towers, is a handsome shell, but was gutted by fire in 1929 and only partly restored. Other attractions on the estate include a circular chapel, an animal farm and an adventure playground for children.