Columbia subject headings:
Harvard subject headings:
Coal mines and mining--Europe--History--Exhibitions.
Coal mines and mining--Germany--Ruhr (Region)--History--Exhibitions.
Coal trade--Europe--History--Exhibitions.
Coal trade--Germany--Ruhr (Region)--History--Exhibitions.
Deutsches Bergbau-Museum Bochum--Exhibitions.
Ruhr Museum (Essen, Germany)--Exhibitions.
Princeton subject headings:
Coal mines and mining--Europe.
Europe--Economic integration--History.
Industrial policy--Europe.