George Stephenson surveyed the route for the North Midland Railway between Derby and Leeds in the 1830s. The route passed close to Ashover where Stephenson saw the potential for the development of a colliery. He formed George Stephenson & Company in 1837 and built a colliery and coke ovens at Clay Cross which opened in 1840. The company passed to his son Robert Stephenson on George's death in 1848, and in 1852 he sold his shares, the business becoming the Clay Cross Company, which was at one time the largest independent employer in the UK.