Engineers working on the £56bn HS2 railway have discovered an ancient, sub-tropical coastline dating back 56m years ago in west London.
The discovery was made at a site in Ruislip, west London when HS2's ground investigation team unearthed a previously unknown material some 33m below the surface.
The layer of black clay, dubbed the Ruislip bed, is thought to have been created from densely wooded marshes on the edge of a sub-tropical sea.
It was discovered when HS2 investigated ground conditions in the area before construction on the Northolt Tunnel gets underway, a 14km tunnel to run from West Ruislip to Old Oak Common.
Steve Reynolds, HS2’s ground investigation programme manager, added:
Since 2015, we have been investigating ground conditions along the route of HS2, so we can design the railway in the safest and most efficient way.
We have been exploring the soil and rocks beneath the surface through various methods, ranging from drilling into the ground and taking samples to using radar technology.
Our main investigations are almost complete, with over 1 million laboratory tests undertaken on the samples we have taken. It’s the largest ground investigation programme that the UK has ever seen and an unparalleled opportunity to learn about the ground beneath our feet.
The initial ground investigation programme on phase one of the railway - from London to the West Midlands - will be largely completed by the end of March.
An exhibition of artefacts unearthed during the construction of the Crossrail project was created after archaeologists uncovered more than 10,000 over the course of the work.
Finds have included a Roman cremation urn, disarticulated skull and bronze coin at Liverpool Street, a Tudor wooden bowling ball at Stepney Green and an 8,000 year-old flint scraper tool from Woolwich.