Somerset is a rural county in the southwest of England, covering . It is bounded on the north-west by the Bristol Channel, on the north by Bristol and Gloucestershire, on the north-east by Wiltshire, on the south-east by Dorset, and on the south west and west by Devon. It has broad central plains with several ranges of low hills. The landscape divides into four main geological sections from the Silurian through the Devonian and Carboniferous to the Permian which influence the landscape, together with water-related features.
The low-lying areas of the North Somerset Levels and Somerset Levels have been subject to thousands of years of flooding and man's attempts to control the flow of water. In the north of the county the Limestone of the Mendip Hills dominates the landscape, while in the south the Blackdown and Quantock Hills rise out of the levels. The highest areas are on Exmoor. The wide variety of landscapes has led to several areas being designated as Sites of Special Scientific Interest for geological reasons, and support a range of flora and fauna as can be seen from the List of Sites of Special Scientific Interest in Somerset.
Rock ages The oldest rocks are of Silurian age (443–419 million years ago), the most southerly known outcrop of rocks of this age in Britain. They make up a sequence of lavas, tuffs (volcanic ash), shales and mudstones in a narrow outcrop to the northeast of Shepton Mallet, in the eastern Mendip Hills.
Rocks from the Devonian (419–359 million years ago) are found across much of Exmoor, the Quantocks (including Hangman Sandstone and Cockercombe tuff), and in the cores of the folded masses of the Mendip Hills.
Carboniferous Period (359–299 million years ago) rocks are represented by the Carboniferous Limestone that forms the Mendip Hills, rising abruptly out of the flat landscape of the Somerset Levels and Moors. The limestones are very fossiliferous, and contain evidence of the abundant marine life that existed at the time of their creation, including fossil crinoids (sea-lilies), corals and brachiopods.
At the end of the Permian (299–252 million years ago) and Triassic periods, the Variscan orogeny resulted in the formation of several mountainous areas including Dartmoor in the south, Exmoor and the Quantocks, and the Mendips.
In the Taunton area Permian (299–252 million years ago) red sandstones and breccia outcrop, although rocks of Triassic age (252–201 million years ago) underlie much of Somerset and form the solid geology of the Somerset Moors and Levels. There are no glacial deposits.
The Triassic rocks consist of red marls, sandstones, breccias and conglomerates which spread over the older rocks. The Dolomitic Conglomerate is an old shingle beach of Keuper Marl age. The Rhaetic Beds are full of fossils due to invasion of the Jurassic Sea. The Lias consists of clays and limestones, the latter being quarried and are famous for their fossils. Blue Lias was burnt locally to provide a source of lime for making lime mortar. It is still used as a decorative building stone. Blue Lias is believed to have been quarried on the Polden Hills as early as the 15th century and was quarried in Puriton from the early 19th century until 1973, when the local cement works closed.Dunning, R.W. (1992). The Victoria History of the Counties of England. A History of the County of Somerset. Volume VI: Andersfield, Cannington and North Petherton Hundreds (Bridgwater and Neighbouring Parishes). Oxford: Oxford University Press. . Page 183.
Above the Lias is the Lower Oolite Series which are chiefly clays and oolitic limestone. The famous Bath Stone is obtained from the Great Oolite bed.Hudson, Kenneth (1971). The Fashionable Stone. Bath: Adams & Dart. .Bezzant, Norman (1980). Out of the Rock.... London: William Heinemann Ltd. . Page 143. Oxford Clay is the chief member of the Middle Oolite Series; and above this are the Upper Cretaceous rocks with Gault, Upper Greensand and Chalk. Alluvial flats and peat bogs occupy much of the centre of Somerset.
Coastline
In prehistoric times the coastline of Somerset was very different from the present one, the sea level at the last glacial maximum being several hundred feet lower than today so that the Bristol Channel was almost non-existent. The Bristol Channel has one of the largest tidal ranges in the world, up to at Burnham-on-Sea for example, behind only the Bay of Fundy and Ungava BayCharles T. O'reilly, Ron Solvason, and Christian Solomon. "Resolving the World's largest tides", in J.A Percy, A.J. Evans, P.G. Wells, and S.J. Rolston (Editors) 2005: The Changing Bay of Fundy-Beyond 400 years, Proceedings of the 6th Bay of Fundy Workshop, Cornwallis, Nova Scotia, Sept. 29, 2004 to October 2, 2004. Environment Canada-Atlantic Region, Occasional Report no. 23. Dartmouth, NS and Sackville, NB. in Canada. Normal high tide may be enhanced by between and during storm surges.Rippon (1997). The Severn Estuary: Landscape Evolution and Wetland Reclamation. London: Leicester University Press. . Chapter 2: "Creation of the Levels" This feature has meant that large areas of the county have been liable to flooding by the sea. Thus the present coastline is partly due to a belt of marine clay at the coast and partly due to seawalls built to reclaim areas previously flooded at high tide.Williams, Michael (1970). The Draining of the Somerset Levels. Cambridge: Cambridge University Press. . Chapter 2: "Draining: The setting of the Somerset Levels". The coastline contains exposures of Devonian sediments and tectonics west of Minehead adjoining the classic exposures of Mesozoic sediments and structural features which extend eastward to the Parrett estuary forming cliffs along the coastline near Clevedon and near Minehead, with low sandhills near Burnham-on-Sea.Rippon (1997). The Severn Estuary: Landscape Evolution and Wetland Reclamation. London: Leicester University Press. . Chapter 1: "Introduction: a regional landscape study". There are sandy beaches mainly at Burnham-on-Sea, Brean and Weston-super-Mare. There are also storm ridges, salt marsh, and sand dunes.
Main river valleys The main valleys between the hills are filled with alluvial deposits from the hills or sea. The county has many small rivers, most of which flow into the Bristol Channel. Many of the latter rivers now have clysts (the local name for a sluice) on them to control the sea, but formerly they were tidal for some way inland. The main exception to this is the River Parrett, which still has a tidal bore. However the Chew and the Frome flow into the Avon which forms most of the northern county boundary with Gloucestershire.Landranger Map 172: Bristol & Bath. Published in 2006 by the Ordnance Survey The Cale flows into Dorset through the Blackmore Vale, while the Exe flows into Devon. The (Dorset) Axe, the Culm and the Otter rise in Somerset but flow into Devon.Landranger Map 193: Taunton & Lyme Regis. Published in 2007 by the Ordnance Survey
The courses of the rivers Parrett, Somerset Axe, Brue and Cary run across the Somerset Levels and have generally been changed to improve the flow.Rippon, Stephen (2007). "Waterways and Water Transport on Reclaimed Coastal Marshlands: The Somerset Levels and Beyond". Chapter 8 In: Blair, John (Edr) (2007). Waterways and Canal-Building in Medieval England. Oxford: Oxford University Press. . The River Axe rises from Wookey Hole Caves, due to water draining into the ground at swallet holes on top of the Mendips. The river passes through Panborough Moor, Wedmore Moor, Ox Moor, Stoke Moor and Mark Moor and reaches the sea at Uphill (near Weston-super-Mare) on Bridgwater Bay.Landranger Map 182: Weston-super-Mare. Published in 2005 by the Ordnance Survey
The River Brue rises at Brewham, close to the county border with Wiltshire. It flows through Bruton and is joined by the rivers Pitt and Alham. The river then flows past East and West Lydford to Baltonsborough and then turns north to Street across Butts Moor, South Moor and Kennard Moor. Originally it then joined the Axe but now it flows west across Westhay Moor, Tealham and Tadham Moors, Chilton Moor, Mark Moor and Huntspill Moor. It is joined by the North Drain and the Hartlake river. In Huntspill Moor the Brue is linked to the man-made Huntspill river by the artificial Cripps river.Williams, Michael (1970). The Draining of the Somerset Levels. Cambridge: Cambridge University Press. . The Brue reaches the sea near Burnham-on-Sea.
The River Cary originates in Castle Cary in the east of Somerset. It flows south-west through Cary Moor to Cary Fitzpaine. The river then turns north-west to the north of Somerton. It then used to turn south to join the Parrett but now passes through Somerton Moor and crosses Kings Sedgemoor in an artificial channel, the King's Sedgemoor Drain, joining the Parrett at Dunball north of Bridgwater.
The River Parrett originates at Cheddington, Dorset, just over the border with Somerset. It enters Somerset at Haselbury Plucknett where it is joined by the Broad river. It passes to the east of South Petherton and flows north through Thorney Moor and Muchelney Level and it is then joined by the Isle and Yeo (Ivel) rivers. The Parrett flows through Langport and then through Middle Moor, Aller Moor to Burrowbridge where it is joined by the River Tone. It then passes through Earlake Moor, Hartlake Moor, Weston Level and South Moor. It continues north through Bridgwater, Horsey Level, past Pawlett Ham and Pawlett Level to the coast near Burnham-on-Sea.
The River Tone originates at Beverton Pond on the Brendon Hills in the west of Somerset. It flows south into Clatworthy reservoir and then to GreenhamLandranger Map 181: Minehead & Brendon Hills. Published in 2006 by the Ordnance Survey where it changes course to go north-east to Taunton. It continues east through West Moor, Curry and Hay Moors and Stan Moor to Burrowbridge where it meets the Parrett.Landranger Map 183: Yeovil & Frome. Published in 2005 by the Ordnance Survey
The River Exe rises at Exehead on ExmoorLandranger Map 180: Barnstaple & Ilfracombe. Published in 2008 by the Ordnance Survey and flows south-east to Exton where it is joined by the River Quarme. It then flows south to Exebridge where it meets the Barle and passes into Devon.Landranger Map 192: Exeter & Sidmouth. Published in 2007 by the Ordnance Survey
Levels and moors
The North Somerset Levels are to the east of Weston-super-Mare, while the Axe valley is separated by the Isle of Wedmore from the Brue valley. The latter is separated by the Polden Hills from the main wetland of the Parrett/Tone/Cary valleys. The Poldens are a low narrow ridge of Blue Lias with alternating bands of limestone and clay. Because of the nature of the Levels and Moors, the Poldens have a significant visual impact.
The Somerset Levels run from the coast up to inland. These wetlands cover , most of which is no higher than above sea level. There are coastal marine clay deposits, and further inland there are many peaty areas. Dotted within this wetland landscape are slightly raised inter-glacial "islands" called burtles. These have been settled from the Mesolithic onward, with wooden causeways linking them to higher ground. There are also rocky outcrops, such as Brent Knoll and Glastonbury Tor which have also housed ancient settlements.Croft, Robert and Aston, Michael (1993). Somerset from the air: An Aerial Guide to the Heritage of the County. Taunton: Somerset County Council. . Chapter 4: "The Somerset Levels and Moors.