"A vast peatland has been discovered in a remote part of Congo-Brazzaville.
The bog covers an area the size of England and is thought to contain billions of tonnes of peat.
Scientists say investigating the carbon-rich material could shed light on 10,000 years of environmental change in this little-studied region.
Dr Simon Lewis, from the University of Leeds, said: "It's remarkable that there are parts of the planet that are still uncharted territory."
He added: "Few people venture into these swamps as they are quite difficult places to move around in and work in.""