Columbia subject headings:
Bituminous coal.
Coal mines and mining--United States.
Coal trade--United States.
United States. Bituminous Coal Division.
United States. National Bituminous Coal Commission.
Harvard subject headings:
Bituminous coal.
Coal mines and mining--United States
Coal trade--United States.
United States. Bituminous Coal Division
United States. National Bituminous Coal Commission.
Princeton subject headings: