Crossrail rock samples stored in Cheshire salt mines

Tonnes of rock samples taken from boreholes drilled as part of Crossrail's construction have been stored in 150m deep salt mines in Cheshire.

The Winsford Rock Salt Mine is the size of 700 football pitches and usually supplies salt to treat frozen roads.

The atmosphere is perfect for the preservation of the rock, some of which dates back millions of years and is thought to hold important geological information.

Work on Crossrail started in 2009 and from 2018 trains will run as far west as Reading in Berkshire and as far east as Shenfield in Essex.

BBC News' Naomi Cornwell speaks to John Davis, an engineering geologist at Crossrail.