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The Geology of Dorset

Submitted by Peter Orchard on Thu, 15/08/2019 - 15:35

This map is a file from the Wikimedia Commons.

Commons is a freely licensed media file repository

Sources: The Dorset Landscape, Its Scenery and Geology - John Chaffey, page 11, ISBN 1 871164 43 5 / Discover Dorset, Geology - Paul Ensom, page 8, ISBN 1 874336 52 0 : 


This is described as a simplified map of the geology of Dorset but it is still pretty complex (but then geology is a complex subject in my view!). To simplify it even further these are the important areas which have an affect the natural history of the county and its rich bio-diversity.


The Purbeck Beds and Portland limestone are extremely important for flora. The Purbeck cliffs and Portland Bill together with the south western ridge are home to many limestone loving flowers, grasses and fungi. Predominantly high cliffs topped with grassland you get superb views of the dramatic Jurassic coast along with some rare plants. Walking can be trying for the less able with some aggressive climbs and descents in places but well worth it if you can manage it. There are places where you can access the limestone grasslands safely, notably Durlston, Portland Bill and the area around the Hardy Monument.


Much of the centre of Dorset is a chalk ridge running from Cranborne Chase in the north east down the west of Dorchester and then a thin strip along the Purbeck Ridge from Lulworth to Ballard Down near Swanage. Calcareous soils, therefore, and chalk loving plants to be found along with more wonderful views.


Cupped by the high chalk ridges is the Poole Basin; a low lying area of sand, gravel and clays that give rise to the unique landscape and environment of the Dorset Heath. Internationally important heath which is home to all six species of indigenous reptiles as well some other rare invertebrates and plants, especially in the more boggy areas. In the centre of the basin is Poole Harbour itself. Said to be the second largest natural harbour in the word it is shallow and quickly reveals large areas of mud flats as the tide recedes and this makes it an incredible place for wintering wildfowl and waders.


To the west of the chalk ridge are an assortment of clays. This gives heavy, damp pasture and some ideal sites for orchids and other plants that need such conditions. West and north Dorset is truly beautiful and gives a feeling that things have gone on unchanged here for centuries.


The Fleet is the name given to the stretch of water that lies behind Chesil beach. Chesil Beach is, itself, one of the natural wonders of Britain but the water behind it is a magnet for wildfowl in winter and features the famous swannery at Abbotsbury of course.


To the extreme west of the county is a further area formed of a limestone called lias. This is the area around Lyme Regis and Golden Cap and some of the highest hills in Dorset, Lewesdon and Pillsden Pen. The coast here is famous for its fossils and the views are amazing and it said that you can see five counties from here including the coast of Wales.

I have tried to allocate the sites I have detailed in the Nature of Dorset to one of these six unique areas. Use the tabs above to see which sites lie within which geological region.