At the start of the Jurassic period the sea level rose dramatically to flood the Triassic desert landscape, and for most of the period tropical seas covered Dorset, and marine life flourished. The sea floor slowly subsided and areas of Jurassic sediments accumulated, filling the deeper parts with mud and shale whilst sand and limestone settled in the shallows. The diversity of conditions and the length of time it took for these to form rock are reflected in the great range of fossils to be found to-day. Within many of the rock layers the quality of preservation is outstanding and as a result the Dorset Coast yields up some of the finest marine fossils of the Jurassic period in the world. The sediments straddle the Jurassic/Cretaceous periods at a time when dinosaurs left their footprints as fossilised trackways.

Later, in the Cretaceous period, the seas again encroached to lay down clays and more sand and, in places, a huge thickness of chalk, spectacularly exposed at the White Nothe, Worbarrow and Durlston Bays and the cliffs at Swanage and Old Harry.

The pattern of thick bands of soft clays, massive bands of chalk and thin bands of hard limestone have influenced the character of the coast. Faults buckled and cut through the strata to form strange features such as Lulworth Cove. Dome shaped folds within the rock have created traps for oil in the thick layer of clay beneath Poole Harbour and Poole Bay where the Wytch Farm oil field is Britain's largest on-shore source of oil.

This Dorset coastline is one of the finest in the World for the formation of rocks and fossils and has given international names to various types of geological substances - amongst them Kimmeridge clay. In the West there are the great landslides around Lyme Regis, the latest at Black Ven in 1958-9. Further East the Chesil Beach stretches from West Bay to Portland and encloses the brackish waters of the Fleet, one of the finest examples of a barrier reef. Portland and its quarries are unique whilst the chalk cliffs of the East rival anything that the cliffs of Dover can offer. It is not surprising that this coastline has attracted many leading scientists including Mary Anning, who discovered and extracted from the beaches at Lyme the first complete fossil specimen of the marine reptiles, Ichthyosaurs and plesiosaurs. To-day collectors follow in Mary Anning's footsteps and, despite over two hundred years of collecting, new discoveries continue to be made.

This coastal diversity contains a stunning wealth of wildlife resulting in a plethora of "sites of special interest" owing much to the underlying geology. Nowhere illustrates the complex relationship between geology and wildlife better than the Isle of Portland where a breathtaking range of internationally rare plants and animals flourish in habitats created by landslides and quarrying.