Columbia subject headings:
Harvard subject headings:
Coal miners--Germany--Dortmund--History.
Coal mines and mining--Germany--Dortmund--History.
Coal trade--Germany--Dortmund--History.
Coking coal--Germany--Dortmund--History.
Zeche Gneisenau--History.
Princeton subject headings:
Coal miners--Germany--Dortmund--History.
Coal mines and mining--Germany--Dortmund--History.
Coal trade--Germany--Dortmund--History.