Geology of England

The chalk outcrop at Flamborough Head in the north produces a headland relatively resistant to coastal erosion whilst the coastline south of this at such places as Mappleton and Hornsea with their soft glacial deposits are vulnerable.

Former ice caps did not reach south of the line running from Bristol to London, so this area has only been impacted by fluvio-glacial deposition which is represented in gravel beds around rivers such as the Thames.

The early geological development of the Avalonia terrane, including England, is believed to have been in volcanic arcs near a subduction zone on the margin of the Gondwana continent.

[2] Some material may have accreted from volcanic island arcs which formed further out in the ocean and later collided with Gondwana as a result of plate tectonic movements.

In the early Cambrian period the volcanoes and mountains of England were eroded as the land became flooded by a rise in sea level, and new layers of sediment were laid down.

Five hundred million years ago, in the Ordovician period, southern Britain, the east coast of North America and south-east Newfoundland broke away from Gondwanaland to form the continent of Avalonia.

The Skiddaw slates of the Lake District consist of metamorphosed marine sediments laid down on the northern margin of Avalonia.

The uplifted regions were gradually eroded down, resulting in the deposition of numerous sedimentary rock layers in lowlands and seas.

[5] Around 360 million years ago during the Carboniferous period, England was lying at the equator, covered by the warm shallow waters of the Rheic Ocean.

During this time Carboniferous Limestone was deposited, as found in the Mendip Hills, in the Peak District of Derbyshire, north Lancashire and the northern Pennines.

The formation of Carboniferous Limestone was followed by the deposition of dark marine shales, siltstones and coarse sandstones of the Millstone Grit, notably in the area later uplifted to form the Pennine anticline.

Later, much of England was submerged in shallow waters as the polar ice sheets melted and the Tethys Ocean and Zechstein Sea formed, depositing shale, limestone, gravel, and marl, before finally receding to leave a flat desert with salt pans.

The remnants of the Variscan uplands in France to the south were eroded down, resulting in layers of the New Red Sandstone being deposited across central England, and in faulted basins in Cheshire.

As the Jurassic period started, Pangaea began to break up and sea levels rose, as England drifted on the Eurasian Plate to between 30° and 40° north.

With much of England under water again, sedimentary rocks were deposited and can now be found underlying much of southern England from the Cleveland Hills of Yorkshire to the Jurassic Coast in Dorset, including clays, sandstones, greensands, oolitic limestone of the Cotswold Hills, corallian limestone of the Vale of White Horse and the Isle of Portland.

Chalk and flints were deposited over much of England, now notably exposed at the White Cliffs of Dover and the Seven Sisters, and also forming Salisbury Plain.

This caused the general lack of land-origin sand, mud or clay sediments around this time – some of the late Cretaceous strata are almost pure chalk.

The Alpine Orogeny that took place from about 50 million years ago was responsible for the shaping of the London Basin syncline and the Weald anticline to the south.

Plant and animal types developed into their modern forms, and by about 2 million years ago the landscape would have been broadly recognisable today.

The most severe was the Anglian Stage, with ice up to 1,000 m (3300 ft) thick in the northwest which thinned considerably as it reached as far south as London and Bristol.

Thought to have peaked around 150,000 years ago, it was named after the town of Wolston south of Birmingham which is considered to mark the southern limit of the ice.

The valleys of the Lake District and parts of the Pennines were further eroded by glaciers, with the ice sheet itself reaching south to Birmingham.

Over the last twelve thousand years during the Holocene epoch the most significant new geological features have been the deposits of peat, as well as in coastal areas that have recently been artificially drained such as the Somerset Levels, The Fens and Romney Marsh.

Since humans began clearing the forest during the New Stone Age, most of the land has now been deforested, speeding the natural processes of erosion.

At the present time, due to Scotland's continuing to rise as a result of the weight of Devensian ice being lifted, England is sinking.

This is generally estimated at 1 mm (1/25 inch) per year, with the London area sinking at double the speed partly due to the continuing compression of the recent clay deposits.

The eastern end of Avalonia collided with Baltica, a continental plate occupying the latitudes from about 30°S to 55°S, as the latter slowly rotated anticlockwise towards it.