Geology – Dorset DSWA

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.

christchurch_tauntonGeological 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		Lambeth Group	Upnor Formation		Sarsens
5	Chalk	Upper Chalk	White Chalk Subgroup	Portsdown Chalk Formation		Flint and Clunch
				Culver Chalk Formation	Spetisbury Chalk Member
				Culver Chalk Formation	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
		Lower Chalk	Grey Chalk Subgroup	Beer Head Limestone Formation	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
6	Greensand		Selborne Group	Upper Greensand Formation	Foxmould Member, Shaftesbury Sandstone and Cann Sand Members	Shaftesbury Stone, ‘Cowstones’
7	Golt Brickearth			Gault Formation
8	Sand		Lower Greensand Group
8	Sand		Wealden Group			Course Quartz Grit
9	Purbeck Stone		Purbeck Group	Durlston Formation	Peveril Point Member	Purbeck Marble, and Burr
				Durlston Formation	Stair Hole Member	Laning Vein, Freestone Vein, and Downs Vein
				Lulworth Formation	Worbarrow Tout Member	New Vein
					Ridgeway Member	Cypris Freestone
					Mupe Member	Cypris Freestone
	Portland Rock		Portland Group	Portland Stone Formation	Portland Freestone Member	Portland Freestone
	Portland Rock			Portland Stone Formation	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
11	Oaktree Clay		Kimmeridge Clay Formation		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
16	Cornbrash		Great Oolite Group	Cornbrash Formation	Lower Cornbrash Member	Cornbrash
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
24	Marlstone			Beacon Limestone Formation	Marlstone Member	Symondsbury and Yeovil Stone
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
				Lilstock Formation	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.