The UK Geology Map

The UK Geology Map

Draw a line from the mouth of the Tees in the north-east to the mouth of the Exe in the south-west. Almost everything about British physical geography sorts itself either side of it. North and west of that line the land is high, rugged and wet, and the rock beneath it is old and hard. South and east of it the land is low, gentle and drier, and the rock is younger and softer. The line is not a coincidence and it is not a rule somebody invented. It is what you get when you look at where the hard rock happens to be, and this module works out why it is there.

Three kinds of rock

How each one formed decides how hard it is, and how hard it is decides what the landscape above it looks like:

Why slate on a roof?

Welsh slate roofed half the buildings in Victorian Britain. Chalk was quarried from the same country in enormous quantities and was never once used for a roof. Both are rock. What is the difference that matters here?

• Slate was formed under great heat and pressure, which aligned its minerals so it splits into thin, flat, strong sheets, and it is hard and impermeable. Chalk is soft, crumbly and porous, so it would neither split into tiles nor keep the rain out
• Slate is dark and chalk is white, and dark roofs absorb more warmth
• Slate is far more common in Britain than chalk
• Chalk is too heavy to lift onto a roof

Two halves of one island

The Tees-Exe line separates two entirely different geological histories:

Label the UK map

This simplified map shows the two broad landscape zones. Drag each label to the correct region.

Find the oldest rock

Tap the region where the UK's oldest rocks are found.

Why is the hard rock there?

It is not a coincidence that the hard rock and the high ground are in the same half of the country. Which explanation accounts for both at once?

• Ancient plate collisions and volcanic activity in the north and west both raised the land AND created the hard igneous and metamorphic rock, by the same heat and pressure. Those rocks then resisted erosion, so the height survived while softer ground elsewhere wore away
• The north and west are wetter and windier, and that weather carved the uplands out of what was flat land
• The south and east were flooded by the sea more recently, which washed away the hard rock and left only soft sediment
• Glaciers pushed the hard rock towards the north and west and left the soft rock behind in the south and east

Geology is not the whole answer

Geology explains where the high ground is. It does not explain what it looks like, and confusing the two costs marks. The detail was cut by ice. During the last glaciation, ice sheets and valley glaciers ground through the uplands, deepening and straightening valleys and gouging hollows out of mountainsides. When the ice melted it dumped everything it had been carrying, which is why much of the lowland is covered by a blanket of glacial debris that has nothing to do with the rock beneath it. Since then rivers and weathering have kept working on it, and for several thousand years so have people, through farming, forestry, quarrying, drainage and settlement. So an exam answer needs both halves: the rock explains the pattern, and the processes explain the shapes. An answer that names only one of them has answered half the question.

Which process made each landform?

What people do with it

The Lake District. Hard volcanic rock and slate, scraped bare by ice, so the soils are thin, stony and acidic and the slopes are steep. Almost nothing arable will grow. What it supports instead: sheep on the fells, forestry on the lower slopes, slate quarrying, and reservoirs, because impermeable rock holds water rather than losing it and the glacial valleys make ready-shaped basins. Settlement is sparse and clings to the valley floors. East Anglia. Soft chalk and clay under a thick blanket of glacial till, weathering into deep, fertile, well-drained soil on almost flat ground, in the driest and sunniest part of Britain. What it supports: some of the most productive arable farming in Europe, dense settlement, and roads and railways that can run more or less straight. Neither region chose its economy. In both cases the rock decided the soil, the soil and the relief decided the farming, and the farming decided where people live.

Where the reservoirs are

The great majority of the UK's large water-supply reservoirs are in the uplands of the north and west, even though most of the demand for water is in the south and east. Give the geographical reason.

• The uplands have the impermeable hard rock that holds water instead of letting it seep away, the deep glacial valleys that can be dammed cheaply at a narrow point, and much the highest rainfall. The lowlands have none of the three
• Land is cheaper in the uplands, so flooding a valley costs less
• Fewer people live in the uplands, so fewer would have to be moved
• Water evaporates less from a cold upland reservoir than a warm lowland one

Which follow from the geology?

Select the THREE statements that follow from what you now know about UK geology.

• Rivers in upland Britain tend to respond to heavy rain quickly and dramatically, while lowland rivers rise more slowly
• Stretches of coast made of hard rock retreat far more slowly than stretches made of clay, so the coastline becomes increasingly ragged over time
• Quarrying tends to be concentrated where the rock is hardest, since that is where the rock is worth extracting for building
• The south and east are flat because they have been eroded for far longer than the north and west
• The ice sheets never reached the lowlands, which is why they have no glacial landforms
• Britain's igneous rock means active volcanoes are still likely in the north and west

The order it happened

Put the making of the British landscape into chronological order, earliest first.

• Plate collisions and volcanic activity build mountains in what is now the north and west, creating hard igneous and metamorphic rock
• Those mountains are worn down over hundreds of millions of years, leaving their resistant roots
• Shallow seas and river deltas lay down soft sediment across what is now the south and east
• Ice sheets and valley glaciers carve the uplands and dump debris across the lowlands
• Rivers and weathering continue to shape the surface after the ice retreats
• People clear woodland, farm, drain, quarry and build across the whole of it

Geology summary

North and west of the Tees-Exe line the rocks are older and harder, because ancient mountain-building and volcanic activity produced _____ and metamorphic rock there; those rocks resist erosion, so the land stands high. South and east the rocks are younger, softer _____ rock laid down in shallow seas, so the land is low. Geology explains where the high ground is, but the shapes were cut mainly by _____. And because upland rock is _____, it holds water rather than losing it, which is where the reservoirs are.