An image issued by HS2 of the Birmingham and Fazeley viaduct, part of the proposed route for the scheme Credit: HS2/PA
An image issued by HS2 of the Birmingham and Fazeley viaduct, part of the proposed route for the scheme (Picture: PA)

An ancient subtropical coastline in west London has been discovered by engineers working on high-speed railway HS2.

A layer of black clay, found 108 feet below the ground, indicates that Ruislip was a woodland marsh by the sea, 56 million years ago.

Dr Jaqueline Skipper, a geological expert working with the HS2 team told The Guardian: ‘When we looked at it in detail, instead of the usual sand and gravel… we had a black clay.’

Undated handout photo issued by HS2 Ltd of part of the black clay layer that was unearthed in Ruislip. An ancient, sub-tropical coastline dating back 56 million years has been found in west London by engineers working on the new high speed rail line. PRESS ASSOCIATION Photo. Issue date: Friday March 16, 2018. The HS2 team unearthed the previously unknown material while carrying out investigations of the ground under the route of the line at 8,000 spots along the first phase from London to the West Midlands. The black clay layer was found up to 33 metres (108ft) below the surface and has been named by HS2 Ltd, the Government-owned company building the railway, as the 'Ruislip Bed'. See PA story ENVIRONMENT Coastline. Photo credit should read: HS2 Ltd/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.
Part of the black clay layer that was unearthed in Ruislip (Picture: PA)

‘This not only had bits of vegetation on it but also showed evidence of extreme weathering of what would have been sand and gravel there before.

‘Suddenly you have got evidence that this is actually the coastline.’

Ground investigations for the first phase of HS2 began in 2015 and have covered about 8,000 locations between London and the West Midlands.

Undated handout photo issued by HS2 Ltd of a computer artist depiction of the Paleocene depiction. An ancient, sub-tropical coastline dating back 56 million years has been found in west London by engineers working on the new high speed rail line. PRESS ASSOCIATION Photo. Issue date: Friday March 16, 2018. The HS2 team unearthed the previously unknown material in Ruislip while carrying out investigations of the ground under the route of the line at 8,000 spots along the first phase from London to the West Midlands. The black clay layer was found up to 33 metres (108ft) below the surface and has been named by HS2 Ltd, the Government-owned company building the railway, as the 'Ruislip Bed'. See PA story ENVIRONMENT Coastline. Photo credit should read: HS2 Ltd/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.
A computer artist depiction of the Paleocene depiction (Picture: PA)

The black clay was found in 2017 in a number of areas along the proposed HS2 route through Ruislip and Northolt.

Dr Skipper, of the Geotechnical Consulting Group added: ‘You have got three-dimensional vision of that was going on – we’ve got trees, we’ve got animals living in trees, we’ve got marshes, we’ve got swamps and we’ve got very nearby beaches.’

The deposit, dubbed the Ruislip bed, is between 19 inches and three feet long and dates back to after the extinction of the dinosaurs, before the end of the Paleocene period.

The initial investigation will be completed by the end of March.

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