Edexcel GCSE Geography

Rock types and where they are found

Rocks are grouped by how they formed, and each group behaves differently when it is attacked by weather, rivers, ice and the sea.

Sedimentary rocks are layered (bedded), often contain fossils and are usually the softest, although they vary a good deal: clay is weak and easily eroded, while chalk and the limestone of the Pennines are more resistant. Igneous and metamorphic rocks are crystalline and generally hard and resistant, because the crystals interlock and there is little water-bearing structure for weathering to exploit.

Because the oldest and hardest rocks lie in the north and west, and the youngest and softest in the south and east, the UK is often described as divided by a line from the mouth of the River Tees to the mouth of the River Exe. North and west of it are the highlands and uplands; south and east of it are lowlands, though the Cotswolds, Chilterns and the Downs are hills formed from more resistant sedimentary rock.

Past tectonic processes and the shape of the land

The UK sits in the middle of the Eurasian plate today, but its rocks record several periods when plates collided, and these set out the broad pattern of upland and lowland.

• Around 450 to 400 million years ago a collision closed an ancient ocean and raised a mountain chain, which was folded, metamorphosed and intruded by magma. Its worn-down remains are the Scottish Highlands, the Southern Uplands, the Lake District and Snowdonia.
• Around 300 million years ago a second collision further south deformed the rocks of south-west England and forced up the large granite masses of Dartmoor, Bodmin Moor and Land's End.
• Around 50 to 30 million years ago the collision of Africa and Europe far to the south, which built the Alps, gently folded the young sedimentary rocks of southern England, tilting the chalk and creating features such as the arch of the Weald and the near-vertical chalk of the Isle of Wight.
• In the north of the UK, volcanic activity around 60 million years ago poured out the basalt of Antrim, which includes the hexagonal columns of the Giant's Causeway.

The result is that upland Britain is mostly formed from igneous and metamorphic rocks, which resist erosion and so survive as high ground with thin soils, steep slopes and poor drainage. Lowland Britain is mostly formed from sedimentary rocks, which wear down more easily into gentle relief and deeper soils, and which carry most of the farmland, towns and population.

Reading geology from maps and sections

A geological map shows which rock lies at the surface, using colours and symbols for each rock and the age of its layers. The British Geological Survey publishes these on paper and online. Lines on the map where different rocks meet show the boundaries, and the width of a band of rock depends on how thick the layer is and how steeply it dips.

A simple geological cross-section is a slice through the ground that shows the order of rock layers and the relief on top of them. Where a hard layer dips gently, it forms a scarp slope (steep, cut across the layers) on one side and a gentler dip slope on the other, as on the chalk of the North and South Downs. Where a hard rock sits next to a soft one, the soft rock forms a lower, flatter area and the hard rock stands up as ridges or hills.

How physical processes shape upland and lowland landscapes

Rock type and structure set the starting point, and a number of processes then act together.

• Glacial erosion and deposition. During the last cold period (the most recent glacial) ice covered most of Scotland, Wales, Northern Ireland and northern England, and reached as far south as the Midlands and the north Norfolk coast. Ice deepened valleys into troughs, scooped out hollows and left steep, bare slopes in the uplands. In the lowlands it laid down till (boulder clay) and moraine, which form many of the gentle hills and flat plains of eastern England.
• Weathering and climate. Frost shattering is strong in the cold, wet uplands, while chemical weathering (for example, rainwater dissolving limestone) is more important where the rock is soluble. Upland rainfall is high, which keeps soils waterlogged and peaty.
• Post-glacial river and slope processes. Since the ice melted about 10,000 years ago, rivers have cut valleys into the glacial landscape, built floodplains and moved sediment downstream. On slopes, soil creep, slumping and rockfalls continue to move material downhill.

Together these explain why upland areas have steep slopes, thin soils, moorland and rough grazing, and why lowlands have gentle slopes, deep soils, floodplains and farmland.

How people have shaped landscapes

Landscapes are also the result of human activity over thousands of years, and in many places people have changed them more than the physical processes have in recent centuries.

• Agriculture. Woodland was cleared from the Neolithic period onwards, field boundaries were laid out (hedges and enclosure walls), the Fens were drained and wetlands were converted to arable land. Upland moors are kept open by sheep grazing, and hillsides carry the dry-stone walls of enclosure.
• Forestry. Large conifer plantations, such as Kielder Forest in Northumberland, have covered former moorland with regular blocks of fast-growing trees, while many ancient broadleaf woods survive in small patches.
• Settlement. Villages, towns and roads, along with quarries and reservoirs, alter the surface and its drainage. Small nucleated villages are common in lowland valleys, and isolated farms in the uplands.

On Ordnance Survey maps, physical features appear as contours, rivers, coasts and the shape of valleys, while human features appear as settlements, roads, field boundaries, woodland symbols, quarries and reservoirs. Telling the two apart, and noticing how they interact (for example, a village sited on a river terrace above the floodplain), is how the landscape of a map is read.