Becher, B. (1991). Pennsylvania coal mine tipples. Schirmer-Mosel.
Cita Chicago (17th ed.)Becher, Bernd. Pennsylvania Coal Mine Tipples. München ; Paris ; London: Schirmer-Mosel, 1991.
Cita MLA (8th ed.)Becher, Bernd. Pennsylvania Coal Mine Tipples. Schirmer-Mosel, 1991.
Atenció: Aquestes cites poden no estar 100% correctes.