Columbia subject headings:
Harvard subject headings:
Coal miners--Germany--Ruhr (Region)--History.
Coal miners--Wales, South--History.
Coal mines and mining--Germany--Ruhr (Region)--History.
Coal mines and mining--Government policy--Germany--Ruhr (Region)--History.
Coal mines and mining--Government policy--Wales, South--History.
Coal mines and mining--Wales, South--History.
Ruhr (Germany : Region)--Economic conditions
Wales, South--Economic conditions.
Princeton subject headings:
Coal mines and mining--Germany (West)--Ruhr (Region)--History.
Coal mines and mining--Wales--History.