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Geology - Introduction

 

Durlston's rocks can be divided into two main types; the Purbeck Limestone series nearest the surface, with the older Portland Limestone series below.

 

The Portland beds were formed in cool, clear sea, about 150 million years ago.

 

The Purbeck beds were formed in a landscape of swamps, ponds and saline lagoons and are about 135 million years old.

 

After these rocks were laid down tectonic forces caused the rock to tilt, break and bend. These tectonic forces were caused by the gradual drifting of whole continents around the globe. 

 

Durlston’s rocks contain an extraordinary record of life in the late Jurassic and early Cretaceous period. Dinosaur footprints, shells, fish scales, sharks, and crocodiles have been found here. These fossils were formed over several millions of years after a complex process known as fossilisation. Firstly the animal had to die, soon after all of the soft parts rot away to leave just the bones or shells. These are then buried by sand and mud. After a long time the sediment builds up on top of the animal and the huge amount of pressure caused by the weight of this turns the animal’s hard parts to stone. A fossil is formed.

 

 

This fossilised crocodile skull, from the Upper Purbeck, was found in 2007 by Richard Edmonds. This animal would have prowled the waters of this area some 135 million years ago preying on anything unfortunate enough to cross its path, from fish to small dinosaurs!!!

 

 

This fossilised crocodile skull, from the Upper Purbeck, was found in 2007 by Richard Edmonds. This animal would have prowled the waters of this area some 135 million years ago preying on anything unfortunate enough to cross its path, from fish to small dinosaurs!!!

 

Although Durlston has some of the most fascinating geology in the world, the characteristics of the rock mean that the cliffs in Durlston Bay are some of the MOST DANGEROUS CLIFFS IN DORSET

 

For fossil hunters the beaches at Charmouth or Lyme Regis are hard to beat.

 

Much of the interesting structure can be seen from the Clifftop Trail and many of the fossils and rocks of both of the Portland and Purbeck series’ can be seen in the Rock Room or in the Fossil Wall at the Learning Centre.

 

Schematic of Durlston Bay (looking west) showing positions of rock units and faults.

A piece of Purbeck Limestone showing footprints of two adult Iguanodon who walked across this drying swamp about 135 million years ago. They were vegetarians that usually walked around on all fours but could stand up on two legs to browse from trees or fight with their formidable thumb claws. They could reach 10m in length and weigh 4-5 tons. You can also some faint desiccation cracks, caused by the drying and shrinking of wet mud..

Geology  - Introduction | The Portland Series | The Purbeck Series | Structure