P. Buurman, A.G. Jongmans, C. Kasse, and B. van Lagen, “Discussion: Oil seepage or fossil podzol? An Early Oligocene oil seepage at the southern rim of the North Sea Basin, near Leuven (Belgium) by E.D. van Riessen & N. Vandenberghe, Geologie en Mijnbouw 74: 301-312 (1996)”, njg, vol. 77, pp. 93-98, Jan. 1998.