The Living World
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Understanding the Geology of the UK

The geology of an area refers to the study and understanding of the area’s solid earth materials (e.g. rocks and minerals), and the processes that have shaped it. The types of substances found in an area can help provide a geographer with a greater picture of the area’s history and the UK’s geology shows a diverse range of rock types and formations.

There are three main rock types:

  • Igneous
  • Sedimentary
  • Metamorphic

The formation process determines the type of rock. The existence of these rocks can tell us a great deal about an area’s geological history, and how the land formed to be as it is today.

The rock cycle shows the transitions between these three main types of rock.

Igneous Rocks: The Fiery Foundation

Igneous rocks form from molten magma that cools and solidifies. These rocks can be found on or below the Earth’s surface. If it is on the surface, it is called extrusive and if it is below the surface, it is intrusive.

In the UK, Igneous rocks are primarily found in mountainous regions like Scotland, Wales and the North of England.

  • The Scottish Highlands have ancient igneous and metamorphic rocks. The oldest rocks, gneiss, are located in the Outer Hebrides and extreme northwest Scotland; they are at least three billion years old.
  • The youngest igneous rocks, around 50 million years old, can be found as basalt lavas on the islands of Skye and Mull.

Sedimentary Rocks: Layers of Earth’s History

Sediment is a material that has broken down through natural processes such as erosion or weathering. It can include rock fragments, minerals and organic matter. Over time, the sediment accumulates and comes under enormous pressure, which causes it to compact. The sediment is then cemented together, forming Sedimentary rocks.

Sedimentary rocks are widely distributed in the UK and can be found in many regions.

  • The Midland Valley is predominantly made up of Old Red Sandstone, a type of sedimentary rock that formed in a desert environment over 350 million years ago. It is often found with carboniferous sediments like sandstone and limestone.
  • The rugged Pennines in Northern England are characterised by hills that are layered with limestone, mudstone, siltstone and sandstone.
  • The Peak District is characterised by Carboniferous limestone and sandstone, including the well-known rock type called Millstone Grit.

Metamorphic Rocks: Altered by Earth’s Forces

Metamorphic rocks originate from pre-existing rocks that have been subjected to high temperatures and pressure. These ‘pre-existing rocks’ can be igneous, sedimentary, or even other metamorphic rocks. The temperature and pressure cause the texture to change without melting, and the rocks formed from these conditions are called Metamorphic rocks.

  • The Southern Uplands in Scotland mainly consist of metamorphosed siltstones and mudstones. Intense heat and pressure have created folds and faults in these metamorphosed rocks.
  • Southwestern England is characterised by strongly deformed Devonian Old Red Sandstone, alongside Carboniferous sandstones and siltstones.
  • In some areas like Bodmin and Dartmoor, you can spot what looks like giant boulders stacked on top of each other, standing out from the landscape. These are called tors and they’re formed from granite. These ‘granite tors’ are formed by layers upon layers of cooled and hardened magma from deep within the Earth, weathered over millions of years to form these unique structures.

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