Dorset's Jurassic Coast

The Dorset and East Devon coastline is England's first natural World Heritage Site and is known as The Jurassic Coast.

The area covers 95 miles and its rocks are 185 million years-old.

As a geologist for the World Heritage Team, Sam Scriven explains, it is a "unique exposure of rocks", which spans the Triassic, Jurassic and Cretaceous periods.

Old Harry Rocks

He says: "The rocks get younger as you travel East to Old Harry Rocks.

"They tell the story of how life has changed and evolved, and how the environment has altered.

"250 million years ago, during the Triassic period, the crust of the earth slowly began to sink and sediment built up, until part way through the Cretaceous period.

"All the layers of rock tilted slightly towards the East and what we see today are slices through those tilted rocks.

"It's the build up of sediment, the structure and shape of the coastline, which gives the rocks this type of exposure."

An ammonite fossil at Lyme Regis

Fascinating fossils

These rocks are best known for their fossils.

Fossils are the remains of plants and animals which were trapped in the rocks millions of years ago.

The Jurassic Coast is famous for its marine fossils - ammonites (from the same family as octopus, cuttlefish and squid), sea shells, snails and giant reptiles such as the ichthyosaur (a dolphin-like reptile) and plesiosaur (which had a long neck).

Sam says: "Charmouth and Lyme Regis have global importance because they have the richest collection in all the world of fish, insects, and giant marine reptile fossils from the Lower Jurassic age [the early part of the period]."

The Cobb at Lyme Regis

Hunting for history

So are people damaging the area by collecting fossils?

Sam describes this as a "contentious issue".

He says: "It is potentially doing some damage, so the important thing is to encourage people to think carefully before they go out fossil hunting - make sure they do their research and attended a guided fossil hunt before they go off on their own.

"We ask them to only collect from loose rocks and never to dig at rocks which have not yet fallen. This is not only damaging but also very dangerous, as rock falls and mudflows are a common occurrence.

"Lyme Regis and Charmouth are eroding rapidly, so these are the best places to look.

"We want to limit fossil collecting in the Portland area, because this is eroding at a much slower rate."

Charmouth landslip - February 2009

"It's all about erosion"

Contrary to popular belief, Sam explains that the tides are not a threat to the coastline.

He says: "It is beautiful because it's eroding - it's all about the erosion.

"Geology doesn't stop a few feet back from the cliff. It will remain wonderful for many years to come - until the whole of Great Britain disappears into the sea."

Rock Around The Coast, a series of guided walks which will, in total, cover the 95 mile coastal path, will take place every Saturday from 30 May until 29 August.