Geology

Dorset is world-renowned for its geological diversity, as exemplified by UNESCO World Heritage Coast (‘Jurassic Coast‘) status.

As first outlined in the early 1800s by William ‘Strata’ Smith, geology underpins the varied landscape of Dorset. Ridges and uplands are formed from resilient sandstone, limestone and chalk (a pure form of limestone) with valleys and lowlands formed from less resilient sands and clays. Although our modern geological understanding is more detailed and complex, it has broadly confirmed William Smith’s pioneering work. Many geological names remain the same as those used by William Smith, often based on older quarrying terms.

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Geological section of Dorset by William ‘Strata’ Smith 1819. Zoom in for more detail. [View/Download]

 
William Smith 1819 Current Geological Nomenclature Building Stone
1 London Clay Barton Group Becton Sand Formation  
Chama Sand Formation  
Barton Clay Formation Hengistbury Head Ironstone
Bracklesham Group Bosconbe Sand Formation  
Branksome Sand Formation Heathstone
Poole Formation Heathstone and Sarsens
Thames Group London Clay Formation Lytchett Matravers Sandstone
2 Clay, Brickearth, Sand and Gravel   Harwich Formation Warmwell Farm Heathstone
3 Crag Lambeth Group Reading Formation West Park Farm Heathstone
4 Sand Upnor Formation Sarsens
5 Chalk Upper Chalk White Chalk Subgroup Portsdown Chalk Formation Flint and Clunch
Culver Chalk Formation Spetisbury Chalk Member
Tarrant Chalk Member
Newhaven Chalk Formation
Seaford Chalk Formation
Lewes Nodular Chalk Formation
New Pit Chalk Formation
Holywell Nodular Chalk Formation
Lower Chalk Grey Chalk Subgroup Beer Head Limestone Formation Zig Zag Chalk Formation Beer Stone, Clunch
West Melbury Marly Chalk Formation Melbury Sandstone
6 Greensand Selborne Group Upper Greensand Formation Bindon Sandstone and Whitecliff Chert Members, Eggardon Grit and Boyne Hollow Chert Members Bindon Sandstone, Chert
Foxmould Member, Shaftesbury Sandstone and Cann Sand Members Shaftesbury Stone, ‘Cowstones’
7 Golt Brickearth   Gault Formation  
8 Sand Lower Greensand Group  
Wealden Group Course Quartz Grit
9 Purbeck Stone Purbeck Group Durlston Formation Peveril Point Member Purbeck Marble, and Burr
Stair Hole Member Laning Vein,
Freestone Vein, and Downs Vein
Lulworth Formation Worbarrow Tout Member New Vein
Ridgeway Member Cypris Freestone
Mupe Member
Portland Rock Portland Group Portland Stone Formation Portland Freestone Member Portland Freestone
Portland Chert Member Chert
10 Sand Portland Sand Formation Gad Cliff Member  
Pondfield Member  
Corton Hill Member ‘Exogyra Bed’ White Cementstone
Black Nore Member  
11 Oaktree Clay Kimmeridge Clay Formation Upper Kimmeridge Clay Dolomitic Limestone
Lower Kimmeridge Clay Dolomitic Limestone
12 Coral Rag and Pisolite or Oolite Corallian Group Abbotsbury Ironstone Formation Ironstone
Sandsfoot Formation  
Clavellata Formation Clavellata Stone
Osmington Oolite Formation Stour Formation Abbotsbury, Todber, Marnhull, Sturminster and Cucklington Stone
13 Sand   Redcliff Formation Hazelbury Bryan Formation  
14 Clunch Clay and Shale Oxford Clay Formation Weymouth Member  
Stewartby Member  
Peterborough Member  
15 Kellaways Stone Kellaways Formation  
16 Cornbrash Great Oolite Group Cornbrash Formation Upper Cornbrash Member Cornbrash
Lower Cornbrash Member
17 Clay & Sand Forest Marble Formation Forest Marble Sandstone
18 Forest Marble   Forest Marble Limestone
19 Clay over the Upper Oolite Frome Clay Formation  
20 Upper Oolite   Wattonensis Beds Member  
  Clay Fuller’s Earth Formation Upper Fuller’s Earth Member  
21 Fuller’s Earth Rock Member   Fuller’s Earth Rock Member Fuller’s Earth Rock
  Clay   Lower Fuller’s Earth Member  
22 Under Oolite Inferior Oolite Group Burton, Beaminster, Sherborne and Hadspen Stone
23 Sand & Sandstone Lias Group Bridport Sand Formation Ham Hill Limestone Member Ham Hill Stone
  Doggers
Down Cliff Clay Member  
24 Marlstone   Beacon Limestone Formation Eype Mouth Limestone Member Symondsbury and Yeovil Stone
Marlstone Member
25 Blue Marl   Dyrham Formation Thorncombe Sand Member Doggers
Down Cliff Sand Member  
Eype Clay Member  
  Charmouth Mudstone Formation  Green Ammonite Member  
Belemnite Marl Member Belemnite Stone
Black Ven Marl Member  
Shales-with-Beef Member  
26 Lias Blue Lias   Blue Lias Formation Blue Lias
27 White Lias Penarth Group Lilstock Formation Langport Member White Lias
Cotham Member  
Westbury Formation  
28 Red Marl Mercia Mudstone Group  
Dorset Geology: showing William Smith’s names and colour scheme, modern geological nomenclature (Group, Formation and Member), usage as building stone. Stones in bold are most commonly used in dry stone walls, though others may have localised use.

 

This geodiversity is reflected in the varied and localised use of stone in dry stone walls and other buildings. Every town, village, hamlet, estate and farm has typically been built from stone from local quarries. Even places only a few miles apart can be built from very different stone that defines their particular character, atmosphere and charm. For more information see Jo Thomas (2008) Dorset Stone, Dovecote Press, Dorset or the Dorset Building Stone website.

In and around the county a wide range of building stone has been used: Blue Lias (Lyme Regis, South Somerset), Beacon Limestone (Symondsbury, Yeovil), Inferior Oolite (Burton Bradstock, Mapperton, Beaminster, Sherborne), Fuller’s Earth Rock (Thornford), Forest Marble (Bridport, West Bexington, Langton Herring, Yetminster, Lillington, Longburton), Corallian Limestone (Abbotsbury, Wyke Regis, Marnhull, Todber), Portland and Purbeck (Isles of Portland and Purbeck), Chert (Morcombelake), Upper Greensand (Shaftesbury), Chalk and Flint (Frome, Cerne and Piddle valleys), Heathstone (Lytchett Matravers). For further geological detail, see our interactive map.

Some prestigious buildings, particularly churches, have used stone from further afield, even ‘imported’ from outside Dorset. For example many church door and window frames use Ham Hill Stone, from just over the border in South Somerset. Such ‘exotic’ stone is rarely found in field walls, though there are exceptions. For example walls around Cerne Abbas may contain Purbeck Stone ‘recycled’ from the ruined Abbey and originally from quarries on the South Dorset Ridgeway.

Dorset is pockmarked with old quarry workings. Many are identified on First and Second Edition OS Maps and are often visible as scars on high resolution LiDAR Digital Terrain Models (See interactive map). The Dorset Area of Outstanding Natural Beauty is rooted in an earlier industrial landscape. However, there are now rather few working quarries which can make sourcing appropriate material for dry stone walling, and other geoconservation projects, rather difficult.

It is hoped the following resources may help you source the ‘right’ stone for a particular location. It is well worth making the effort.