Columbia subject headings:
Harvard subject headings:
Battlefields--Europe--Pictorial works.
Battlefields--Europe.
Military geology--Europe.
World War, 1914-1918--Campaigns--Western Front
World War, 1914-1918--Campaigns--Western Front--Pictorial works.
Princeton subject headings:
Geology--France.
Military geology--History.
World War, 1914-1918--Campaigns--France.