Most of Cornwall and parts of Devon were formed millions of years ago when a section of France collided with Great Britain, according to a new study.
England, Wales and Scotland were previously thought to have formed when the ancient landmasses of Avalonia and Laurentia merged over 400 million years ago.
Now, geologists from the University of Plymouth have found evidence in the rocks of south west England that suggests the region is quite distinct from the rest of the country.
Deposits left by underground volcanic eruptions across the region suggest the landmass of Armorica, which contains modern-day France, also played a part in creating Britain.
Dr Arjan Dijkstra, who led the study, said this was a “completely new way of thinking about how Britain was formed”.
“It has always been presumed that the border of Avalonia and Armorica was beneath what would seem to be the natural boundary of the English Channel,” he said.
“But our findings suggest that although there is no physical line on the surface, there is a clear geological boundary which separates Cornwall and south Devon from the rest of the UK.”
The researchers examined 22 sites across Devon and Cornwall, and found a boundary that runs roughly from the Exe estuary in the east to the town of Camelford in the west.
Rock samples from these ancient sites were taken back to the lab and subjected to intense chemical analysis to understand their past. The scientists published their findings in the journal Nature Communications.
In more recent history, Britain was connected by a land bridge to mainland Europe that allowed humans and animals to migrate between the regions, but the new discovery shows an even deeper connection.
“We always knew that around 10,000 years ago you would have been able to walk from England to France,” Dr Dijkstra added.
“But our findings show that millions of years before that, the bonds between the two countries would have been even stronger.
“It explains the immense mineral wealth of south west England, which had previously been something of a mystery, and provides a fascinating new insight into the geological history of the UK.”
The South West contains an abundance of valuable metals like tin and tungsten. These metals are also found in Brittany and other parts of mainland Europe, but are not common throughout the rest of the UK.