Columbia subject headings:
Coal miners--Germany--Ruhr (Region)--Personal narratives.
Coal miners--Germany--Ruhr (Region)--Social life and customs.
Harvard subject headings:
Coal miners--Germany--Ruhr (Region)--Personal narratives.
Coal miners--Germany--Ruhr (Region)--Social life and customs.
Princeton subject headings:
Grän, Moritz.
Miners--Germany (West)--Ruhr (Region)--Biography.