Howard Falcon-Lang, a palaeontologist at Royal Holloway, University of London, said yesterday that glass slides containing important Darwin fossils were in an old wooden cabinet in the British Geological Survey.
Using a torch to peer into the drawers and hold up a slide, Dr Falcon-Lang saw one of the first specimens he had picked up was labelled ''C. Darwin Esq''.
''It took me a while just to convince myself that it was Darwin's signature on the slide.'' He described the feeling of seeing the famous signature as ''a heart-in-your-mouth situation''.
Dr Falcon-Lang's find was a collection of 314 slides of specimens collected by Darwin and other members of his inner circle.
The first slide pulled out of the dusty corner at the British Geological Survey turned out to be one of the specimens collected by Darwin during his famous expedition on HMS Beagle, which changed the young Cambridge graduate's career and laid the foundation for his subsequent work on evolution.
Dr Falcon-Lang said the fossils - lost for 165 years - showed there was more to learn from a period of history scientists thought they knew well.
''To find a treasure trove of lost Darwin specimens from the Beagle voyage is just extraordinary. There are a lot of very, very significant fossils in there that we didn't know existed.''
He said one of the most ''bizarre'' slides was a specimen of prototaxites, a 400-million-year-old tree-sized fungi.