Columbia subject headings:
Coal miners--United States.
Coal mines and mining--United States.
Coal trade--United States.
United States. Coal Commission.
Harvard subject headings:
Coal miners--United States
Coal mines and mining--United States
Coal trade--United States.
United States. Coal Commission.
Princeton subject headings:
Coal miners--United States.
Coal mines and mining--United States.
Coal trade--United States.
United States. Coal Commission