Geology of the Severn Estuary

Beneath the trees, grasses and soils of the Severn Estuary, there is a world of hidden history. This history lies within the bedrock underground. Bedrock refers to the many different types of rock that make up the land. These rocks were once at the surface, where dinosaurs walked, and ancient trees grew.

Bedrock is deposited in layers, one by one, which makes up the landscape. Movements of the earth’s continental plates can cause these layers to bend, fold and twist due to the huge forces at play. This means that different places around the UK have different patterns of rock, which are spectacular to observe!

The main types of rock along the Severn Estuary are mudstone, sandstone and lias (a mixture of limestone, shales and clays). They date from 200 – 359 million years ago, covering the Devonian, Jurassic and Triassic time periods. These are sedimentary rocks, which means they are made out of sediment: sand, gravel and silt. Over time, they are buried deeper and deeper. This means that they become ‘squashed’ and solidify into rock.

The two other rock types, igneous and metamorphic are not found along the estuary. Igneous rock is formed from solidified magma, such as that erupted from a volcano. Granite is a common igneous rock across moorland in Devon and Cornwall. Metamorphic rock occurs where sedimentary rock is under so much pressure, that it changes. Common metamorphic rocks are marble and slate.

At Aust Cliff, south Gloucestershire, spot the bright layers of red, white and black rock. These record a history where the UK was once a tropical paradise – unlike the rainy weather we experience today. Go to Explore the Severn, Aust Cliff, to discover more about the history and geology of this area.

Safety on the Severn

Remember to explore exposed rock and cliffsides safely. Do not stand under cliffsides or pull loose rock from them. Remember to be aware of incoming tides when exploring beaches and rockpools. For more safety advice.

Time to explore…

To explore the rocks along the Severn Estuary and find out more about them, visit the British Geological Survey’s Geology Viewer website. This displays an interactive geological map of the UK. You can zoom into the Severn Estuary to see each rock type clearly marked on the map.


Discover the many projects the Severn Estuary Partnership are involved with across the area.

Sandstone Rock (Photo credit Paul Trafford, 2017)

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