The Black Country is an area of the West Midlands county, England covering most of the Metropolitan Boroughs of Dudley, Sandwell and Walsall. Dudley and Tipton are generally considered to be the centre. It became industrialised during its role as one of the birth places of the Industrial Revolution across the English Midlands with coal mines, coking, iron foundries, glass factories, brickworks and steel mills, producing a high level of air pollution. The 14-mile (23 km) road between Wolverhampton and Birmingham was described as "one continuous town" in 1785.