Cornish Geology

geology of a cliff face

Cornish geology is fascinating. 

Piecing together its geological time line has been a long and difficult job for hundreds of geologists.

Travel back in time to find out how the geology of Cornwall formed what you can see in the landscape today.

The Cornish landscape that we know today was created over millions of years.

From the beginning….

13 billion years ago, a tiny fireball of infinite mass and heat exploded. Sizzling light and heat flew out forming a hot particle soup. This created the Universe which has been evolving and expanding ever since.

Out of this expanding ball of energy, matter was formed and drawn together by gravity to form the first stars and planets.

About 4.6 billion years ago our Sun, Earth and solar system formed. The early Earth was a ball of molten rock. As this cooled, the outer surface solidified to form a crust.


The crust of the Earth is made up of a number of interlocking pieces called ‘plates’ that move relative to each other, at the same rate as your fingernail grows. This slow movement means that the face of the earth is constantly changing.

About 400 million years ago near the equator, lay a shallow sea where sediment washed from surrounding landmasses was being deposited in layers to later become sedimentary rock.

Over the next 100 million years, the landmasses collided, lifting up and crumpling these layers to form mountains.

The great stresses involved in this activity converted the sediment into metamorphic rocks, which would later be known in Cornwall as Killas.

Some of the rock was also forced down deeper into the Earth, where it melted to form a pool of molten rock called magma.

This magma would eventually cool to form a mass of granite deep underground called a batholith. The magma and hot granites from inside the earth rose and cooled to form the backbone of Cornwall. As the batholith continued to cool, vertical cracks opened up in the granite and the surrounding rock, through which mineral-rich fluids were able to flow. Eventually the fluid cooled sufficiently to allow these minerals, such as tin, to be deposited in the cracks to form mineral veins or lodes. Tin and copper await the arrival of man 250 million years later.

Over the next 300 million years, the mountain chain was continuously moved northward and eroded to partly expose the underlying granite batholith.

The final shaping of the landscape was brought about by rapid climate change over the last 3 millions years. This included many ice ages and sea-level rise-and-falls, which exposed the mineral lodes and created the Cornwall we see today.


Photograph reproduced with the kind permission of the Geevor Archive

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Comment left by trelawney.pol on 2013-09-09 18:23:32

well explained & very educational.great

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