Lesson 2. Geological background and relief of Great Britain.

The British Isles consist of England, Scotland, Wales and Northern Ireland, which make up the United Kingdom and the Republic of Ireland (Eire). It is situated between latitudes 50N and 61N, and has a great variety of natural landscapes, which have developed from different underlying rocks.

The youngest rocks are to the south and east of a line drawn from the mouth of the river Tees to the mouth of the river Exe.

There are three types of underlying rocks and all of them can be found in Great Britain. IGNEOUS rocks are formed from hot, molten material or MAGMA, which is found deep beneath the Earth’s crust. Magma is sometimes forced towards the surface. When it flows on the surface it is called LAVA. The largest outcrop of basalt, igneous lava, is the Antrim Plateau area of Northern Ireland. Granite is another igneous rock. It has cooled and solidified beneath the surface. Outcrops of granite exposed by erosion are found in Dartmoor and several areas of Scotland.

SEDIMENTARY rocks are made from eroded material, which is compressed and hardened into layers or STRATA:

COAL was mostly formed in the Carboniferous period (about 300 million years ago). It is carbon from remains of tropical swamps and forests. Coal is found to the north and west of Tees-Exe line.

SANDSTONE is cemented sand: old red and new red sandstone deposited in times of a hot desert climate. Sandstone is found in Exmoor, Midland Plain and Weald.

CHALK is formed from the remains of marine animals. Bands of chalk may be found across lowland England.

LIMESTONE is mixed remains of marine animals or chemical deposits. Harder older limestone - carboniferous limestone makes up parts of Pennines. Younger Jurassic limestones outcrop from Cotswolds to North York Moors.

CLAY is presented by fine deposits of silt and mud and may be found in vales of basins of southern and eastern England - London Basin and to the south of it.

METAMORPHIC rocks have been changed by heat and pressure (‘Metamorphosis’ means great change). Shale is changed to slate (e.g. in North Wales). In northern Scotland, gneisses and schists are the changed forms of igneous rocks.

The British Isles rise from the western edge of a broad continental shelf and are structurally a part of Europe. The same Earth movements influenced both the British Isles and the continent.

Three mountain-building periods have affected the rocks and the relief of the British Isles. The earliest, the Caledonian, produced the mountains of Wales, the Lake District and Scotland. A later period, Hercynian, folded the rocks of south-west England, the Midlands and South Wales to form a lower, more hilly relief.

The most recent movement, about 35 million years ago, centred on Alpine Europe, but “ripples” affected southern England. The SYNCLINES or downfolds of the London and Hampshire Basins were formed. The ANTICLINE or upfold of the Weald of Sussex and Kent was a result of these ripples.

WEATHERING, EROSION and DEPOSITION have added further variety to the physical geography of the British Isles.

The influences of the ICE AGE can be seen in many parts of the country. Glacial erosion moulded the mountains of highland Britain. Glacial deposits (moraines, outwash material and boulder clay) have been left over much of lowland England. Only the south of England was untouched by ice.

The melting of ice-sheets raised the sea-levels around Britain. Only 8000 years ago, England was finally separated from the continent of Europe. The rising sea-levels formed the inlets, creeks and natural harbours of the coast of southern and eastern England. The rias (drowned river valleys) of Devon and Cornwall and sea-loch or fiords of western Scotland were the result of rising sea-levels.

Relief.

In spite of the comparatively small area, the British Isles have a great variety of surface features. They reflect a long and complex geological history of the archipelago. Such complexity makes it difficult to describe the relief of the British Isles, but the usual way of dividing it is into “Highland Britain” and “Lowland Britain”. These two areas are separated by Tees-Exe line.

To the north and west of this line are hills and mountains that resisted weathering and erosion. Highland Britain comprises the entire Scotland, the Lake District, the Pennines, almost the whole of Wales and Cornwall peninsula.

The highest mountain of Great Britain is Ben Nevis (1343 m), that is in the Grampians in Western Scotland.

To the south and east of Tees-Exe line the rocks have been eroded into a plain, more often rolling than flat. The Lowlands are subdivided into the Midland plains and plains of East Anglia and South-East of England.

Scotland: Northern Highlands

The Grampians

Central Plain

Southern Uplands

The Cheviots separate England from Scotland.

England: The Cumbrians (Lake District)

The Pennines

Cornwall Upland

The Fenlands (the Fens)

The London Basin

The Midlands

The Hampshire Basin

The Weald

Wales: The Cambrians (Snowdon - 1085 m)

Wales is entirely an upland region. South Wales consists of a great plateau, which is a coalfield.