This spectacular slide shows the cross-section of a cone of a monkey-puzzle tree.

A rare collection of fossils, including some collected by Charles Darwin, has been 'rediscovered' at the British Geological Survey (BGS).

The fossils, which had been 'lost' for 165 years, have now been photographed and are available to the public through a new online museum exhibit.

Dr. Howard Falcon-Lang, a palaeontologist at Royal Holloway, University of London was in the BGS archive looking for carboniferous fossil-wood specimens when he made the discovery.

"I spotted some drawers marked "unregistered fossil plants", he recalls. "I can't resist a mystery, so I pulled one open. What I found inside made my jaw drop!"

Inside were hundreds of fossil plants, polished into thin translucent sheets known as 'thin sections' and captured in glass slides so they could be studied under a microscope.

Falcon-Lang's jaw dropped even further when he began to take out the slides. One of the first he looked at was labelled 'C. Darwin Esq.'

"This turned out to be a piece of fossil wood collected by Darwin during his famous voyage on the Beagle in 1834,' says Falcon-Lang, 'the expedition on which Darwin first began to develop his theory of evolution."

It turns out that botanist Joseph Hooker, long-time director of Kew Gardens and Darwin's best friend, had assembled the collection at the start of his career during a brief stint at BGS in 1846. Among the specimens were some found by Hooker himself during an Antarctic voyage in 1840. Others seem to have come from the cabinet of the Revd John Henslow, Darwin's mentor at Cambridge whose daughter later married Hooker.

The collection shows how wide a net had already been cast by British scientists in the early 19th century. As well as items from well-known British fossil sites like the Isle of Portland in Dorset, it includes fossil wood from the Caribbean, Australia, Egypt, India and the Far East.

This slide shows a cross-section through a quite amazing fossil tree from Scarborough, Yorkshire, England. Jurassic Period, 180 million years old.

It is also significant for the light it sheds on the development of geological studies; some of the thin sections in the collection are among the first ever made by William Nicol, the pioneer of petrography, in the late 1820s.

The collection may have slipped into obscurity partly through bad timing; Hooker had set off on an expedition to the Himalayas by the time BGS's formal 'specimen register' was established in 1848. When he got back, in 1851, the collection was being moved to the Museum of Practical Geology in Piccadilly and the opportunity for him to label the fossils had passed. In 1935 the collection moved again, to the Geological Museum in South Kensington.

Finally, 50 years later, the fossils returned to BGS and were placed in their storage facility at Keyworth near Nottingham. BGS is home to more than three million fossils, collected and recorded with precision over two centuries. But with each move the significance of Hooker's uncatalogued collection had gradually passed out of memory.

BGS specialists soon confirmed that the antique specimens had been gathered from around the world and despite its years in the wilderness the origins and importance of Hookers collection are now being revealed.

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This story is republished courtesy of Planet Earth online, a free, companion website to the award-winning magazine Planet Earth published and funded by the Natural Environment Research Council (NERC).