Geography of Dorset
is a county located in the middle of the south coast of England. It lies between the latitudes 50.512°N and 51.081°N and the longitudes 1.682°W and 2.958°W, and occupies an area of 2,653 km2. It spans from east to west and from north to south.
The geology of Dorset is varied; most of the different rocks found in the wider south-east of England outcrop within its boundaries. The oldest rocks are found in the west of the county; a general progression eastwards reveals younger strata formed in the Middle and Late Jurassic epochs, and the Cretaceous and Paleogene periods. Many of the sea-cliffs in the county, particularly around the town of Lyme Regis, are very rich in exposed fossils.
Dorset's terrain is lowland in nature, albeit hilly in many parts. The highest point in the county is Lewesdon Hill, 279m above sea-level. The landscape of much of the county comprises hills formed by strata of the Chalk Group; these hills include the Dorset Downs, parts of the South Dorset Downs, and the Purbeck Hills. To the north of the Dorset Downs is the Blackmore Vale, a relatively low-lying area of clays and limestones of Jurassic age. The south-east of the county forms part of the Hampshire Basin, an asymmetric syncline covered in sands and gravels of Paleogene age.
The main rivers in the county are the Stour, Frome and Piddle. The Stour is the county's largest river, although its source is in the neighbouring county of Wiltshire. The Frome and Piddle both lie wholly within the county.
The whole of Dorset's coastline is designated part of the Jurassic Coast World Heritage Site, and contains examples of many different coastal landforms, reflecting the variety of the underlying geology. At 191m Golden Cap is the highest cliff on the south coast of England.
The natural resources of Dorset again reflect its particular geology. Western Europe's largest onshore oilfield lies under the south-east of the county. Portland stone and Purbeck limestone have both been quarried for centuries to provide construction material for buildings around the world. Purbeck ball clay is quarried for use in the production of fine pottery.
The predominant land use in Dorset is agriculture. On the chalk hills this is largely arable, whereas in the valleys and vales it is more mixed with pasture. The sand and gravel soils between the towns of Dorchester and Poole were historically covered in heathland, although much of this is now afforested. 53% of the county is designated as being an Area of Outstanding Natural Beauty, and there are 139 Sites Of Special Scientific Interest, covering an area of.
Dorset is a largely rural county; the county's largest and only major urban area is the South East Dorset conurbation, based on the towns of Poole, Bournemouth and Christchurch, with a combined population of around 400,000. The population of the county overall is 714,900. The conurbation has a green belt surrounding it to prevent urban sprawl and afford other protections to the wider area.Area
Dorset is a county in the middle of the south coast of England. It lies between the latitudes 50.512°N and 51.081°N and the longitudes 1.682°W and 2.958°W, and occupies an area of 2,653 km2. It spans from east to west and from north to south.
For local government purposes, Dorset is divided into two unitary authorities. Bournemouth, Christchurch and Poole, in the south-east of the county, takes in most of the South East Dorset conurbation, while the remainder of the county is administered by the Dorset unitary authority. Until local government reforms in 2019, most of the county was served by the Dorset County Council, while Poole and Bournemouth were unitary authorities.Geology
The geology of Dorset is varied; most of the different rocks found in the wider south-east of England outcrop within its boundaries. The geological structure of the county is easily visible in places, making Dorset a suitable place for geological study. The rocks outcropping in Dorset are all of sedimentary origin, and were formed in the Jurassic, Cretaceous and Paleogene periods of geological history. The oldest rocks are found in the west and north of the county, the youngest in the east. The south-east of the county occupies the western end of the Hampshire Basin, an asymmetric syncline which underlies a large part of central southern England.Hills and vales
Dorset Downs
The Dorset Downs are chalk hills formed by strata of the Chalk Group, a geological unit which also covers much of southern and eastern England. The chalk which comprises the downs was formed in the Cretaceous period, when the area now known as Dorset was below sea-level. The Dorset Downs are the largest outcrop of the chalk within Dorset, and occupy much of the central part of the county. They stretch northeastwards from Eggardon Hill and Beaminster Down in the west of the county, to Bell Hill and Shillingstone Hill overlooking the River Stour near Blandford Forum. The chalk hills continue on the other side of the Stour Valley as Cranborne Chase. The Downs are part of the northern rim of the Hampshire Basin, which dips gently to the southeast from the steep north-facing scarp slope. The dip slope of the chalk is incised by seasonal streams or winterbornes, which have formed several roughly parallel valleys aligned north to south.Blackmore Vale
The Blackmore Vale is a broad vale of relatively low-lying land in the north of the county. Its boundary is indistinct, but roughly conforms to that part of the catchment area of the River Stour that lies north of the Dorset Downs and west of Cranborne Chase. It partly lies within south Somerset. The underlying rock strata are mostly of Jurassic age, comprising broad bands of clay separated by narrower bands of limestone, with a narrow outcrop of Early Cretaceous Greensand and Gault clay close to the chalk hills. The alternating bands of clay and limestone result in the floor of the vale being gently undulating rather than flat.The Marshwood Vale is a bowl-shaped valley in the extreme west of the county. Its floor is composed of Lower Lias clay which produces wet ground most suitable for pasture. It is drained by the River Char, which flows southwest to the coast at Charmouth. It is surrounded by hills, including the two highest points in the county, Lewesdon Hill and Pilsdon Pen.Purbeck Hills
The Purbeck Hills are a line of chalk hills running roughly east to west along the centre of the peninsula known as the Isle of Purbeck. They are formed of chalk of the same Chalk Group as the Dorset Downs to the north; beyond the Purbeck Hills the visible chalk extends westwards into the South Dorset Downs, which join the northern downs west of Dorchester. The Purbeck Hills are a monocline, a step-like geological fold dating from about 30 million years ago, resulting from the same collision of tectonic plates which built the Alps. Gaps in the ridge at Corfe Castle and Arish Mell are due to faults causing weakening of the chalk.Cranborne Chase
Cranborne Chase is composed of a continuation of the same chalk strata which form the Dorset Downs to the south-west; it is divided from the Downs by the valley of the River Stour, which cuts through the chalk at Blandford Forum. Cranborne Chase lies partly within the neighbouring county of Wiltshire. It is a sparsely populated area that is well-wooded in parts. The name 'chase' comes from its previous use as a hunting area.Rivers and lakes
River Stour
At 60 miles in length, the River Stour is Dorset's longest river, although its source is just outside the county boundary at Stourhead in Wiltshire to the north. It enters Dorset near the village of Bourton, then flows generally southwards through the Blackmore Vale via the towns of Gillingham and Sturminster Newton. Virtually the whole of the Blackmore Vale is within the Stour's catchment area. It leaves the Blackmore Vale in a deep valley which it has cut through the chalk hills; it hence forms the divide between the Dorset Downs to the southwest and Cranborne Chase to the northeast. It is the only one of Dorset's rivers to pass through the chalk in this way. It then flows generally southeastwards through Blandford Forum and around the northern suburbs of Bournemouth, to enter the English Channel through Christchurch Harbour. It is tidal for about the last 3 miles. The main tributaries of the Stour are the River Cale and River Lydden in the Blackmore Vale, and the Moors River and River Allen which join the Stour in its lower reaches after it has passed through the chalk.River Frome
At 30 miles in length, the River Frome is only half the length of the Stour, however unlike the Stour, the Frome lies wholly within the county boundary, rising in the village of Evershot on the Dorset Downs, and entering the English Channel through Poole Harbour. Its catchment area is 181 square miles, or one sixth of the county. It also differs from the Stour in that in its upper reaches it is a chalk stream, and even when it leaves the chalk and flows over acid sands and gravels east of Dorchester, its load of sediment from the chalk is sufficient to counteract the acidity and create fertile pasture and watermeadows. The main tributaries of the Frome are the River Hooke and River Cerne.River Piddle (River Trent)
The River Piddle follows a similar and almost parallel course to the Frome, rising a few miles to the east on the chalk downs near the village of Alton Pancras, then flowing roughly southeastwards through chalk and over sands and gravels to reach the English Channel through Poole Harbour. Along its course it gives its name to several villages, each bearing the prefix 'Piddle' or 'Puddle'. The Piddle is the only river in Dorset to have an alternative name.Other rivers
There are several smaller rivers and streams in Dorset which do not form part of the catchments of either the Stour, Frome or Piddle. Many of these drain short tracts of land between coastal hills and the English Channel. In the extreme west, the River Char drains the Marshwood Vale and enters the Channel at Charmouth. The River Brit rises north of Beaminster, flows south through Bridport and enters the Channel at West Bay. Near the village of Burton Bradstock, about 1 mile east of the mouth of the Brit, is the terminus of the small River Bride; this rises at Bridehead in the hills between Dorchester and Bridport, and flows westwards for about seven miles "before sinking into the shingle" of Chesil Beach. Further east along the coast is the River Wey, which flows into Radipole Lake in Weymouth, and enters the Channel through Weymouth Harbour.