HS2 excavations uncover prehistoric subtropical coastline in Ruislip, west London

Black clay deposit indicates the London suburb was once a woodland marsh by the sea

It was a time when Britain boasted a subtropical climate, dense forests and parts of the south and east of country were under a shallow warm sea. But in Ruislip, west London, you would have needed your wellingtons: 56m years ago, the area appears to have been a wooded marsh.

Experts working on exploratory excavations for the high-speed railway HS2 say that samples taken from up to 33 metres below the surface in Ruislip contained a previously unknown material which suggests that in the late Paleocene epoch the region was a swampy area, in close proximity to the sea.