British scientists have discovered a "treasure trove" of lost fossils, some collected by Charles Darwin more than 150 years ago.

The fossils were found quite by chance, the Royal Holloway University of London said in a news release Tuesday. They were in a dusty old cabinet at the British Geological Survey, labelled "unregistered fossil plants."

"I can't resist a mystery, so I pulled one open," Dr. Howard Falcon-Lang said. "What I found inside made my jaw drop."

The collection consists of hundreds of "beautiful glass slides" made by polishing fossilized plants into thin translucent sheets so they can be examined under a microscope.

"Almost the first slide I picked up was labelled 'C. Darwin Esq,'" Falcon-Lang said. It turned out to be a piece of fossil wood collected by the famed naturalist during his 1834 voyage — the expedition that led him to formulate his theory of evolution.

Joseph Hooker, a botanist and friend of Darwin's, worked at the British Geological Survey in 1846, where he assembled the collection of fossils obtained by Darwin and others, but he never finished cataloguing them, according to the release.

The fossils were moved several times before landing back at the BGS. They've been photographed and posted for the public in an online exhibit on the BGS's website.