Columbia subject headings:
Harvard subject headings:
Mineral industries--Germany--Harz Mountains--History--Congresses.
Mining engineering--Germany--Harz Mountains--History--Congresses.
Mining engineers--Germany--Biography--Congresses.
Princeton subject headings:
Mineral industries--Germany--Harz Mountains--History--Congresses.
Mining engineering--Germany--Harz Mountains--History--Congresses.
Mining engineers--Germany--Biography--Congresses.