The black country according to some is where the coal seam was ,also the industry ,bilston had industry ,but wasn't in Wolverhampton at the time.
Walsall had coal close to the surface .what wiki says ...
Until the late twentieth century, the Black Country had no officially defined borders.[6] Some traditionalists have tended to define it as "the area where the coal seam comes to the surface – so West Bromwich, Oldbury, Blackheath, Cradley Heath, Old Hill, Bilston, Dudley, Tipton, Wednesfield and parts of Halesowen, Wednesbury and Walsall but not Wolverhampton, Stourbridge and Smethwick