Columbia subject headings:
Bituminous coal.
Coal miners--United States.
Coal mines and mining--United States.
Coal trade--United States.
Hours of labor--United States.
Wages--United States.
Harvard subject headings:
Bituminous coal.
Coal miners--United States
Coal mines and mining--United States
Hours of labor--United States
Wages--United States.
Princeton subject headings:
Bituminous coal.
Coal miners--United States.
Coal mines and mining--United States.
Hours of labor--United States.
Wages--United States.