A 300-million-year-old forest, containing well-preserved examples of plants that have long since become extinct, has been discovered in a coal mine in the US state of Illinois.

Writing in the journal Geology, scientists from the University of Bristol and several US institutions said that the fossilised forest is the largest ever found, covering a 10,000-hectare area revealed after seams of coal were removed.“We walked for miles and miles along pitch-black passages with the fossil forest just above our heads,” explained Dr Howard Falcon-Lang from the University of Bristol. “We were able to make a map of the forest by the light of our miner’s lamps.

”The forest dates back to the Carboniferous period – when most of the world’s coal reserves were formed – and provides a unique snapshot into the ecology of the time, allowing scientists to track how species have evolved and landscapes have changed.The scientists believe that the forest’s state of preservation is the result of the whole region dropping below sea level and becoming buried in mud after a major earthquake.