1. The Occurrence of Coal-Balls in No. 6 Coal Bed at Nashville, Illinois;Cady;Trans. Ill. Acad. Sci.,1936
2. The Relation of Concretions to Coal Seams;Feliciano;J. Geol.,1924
3. Review of American Coal-Ball Studies;Noe;Trans. Ill. Acad. Sci.,1931
4. A Comparative Study of Upper Chester and Lower Pennsylvanian Stratigraphic Variability;Potter;J. Geol.,1955
5. Preservation of Plant Material in Coal-Balls from Nashville, Illinois;Schopf;Trans. Ill. Acad. Sci.,1936