Land from ancient France is now part of Devon and Cornwall, geologists studying how Britain was formed have revealed.
Their theory comes after studying the chemical profile of the west country counties’ rocks, which have more in common with France than the rest of the UK.
For centuries scientists thought England, Wales and Scotland were created by the merger of two land masses more than 400 million years ago.
Earth’s continental fragments were on the move and Avalonia, which would become England and Wales, collided and fused with Laurentia, which would become Scotland.
Experts now now believe a third land mass – Armorica, which includes Brittany and Normandy – was also involved in the process.
It had been thought the border between Avalonia and Armorica lay beneath the English Channel.
Scientists based at the University of Plymouth have shown that the geological border in fact runs from the Exe estuary, on the south coast of Devon, in the East to the north Cornish town of Camelford, in the west.
The new way of thinking about the creation of Great Britain was based on an extensive study of mineral properties at exposed rock features across Devon and Cornwall.
They reveal a clear boundary running across the two counties, with areas north of it sharing their geological roots with the rest of England and Wales but everything south being geologically linked to France and mainland Europe.
This could explain the abundance of tin and tungsten in the far South West of England, metals also found in Brittany and other areas of mainland Europe, but not so evident in the rest of the UK.