P. Buurman, and A. W. Janssen. “The Stratigraphic Position of the Enigmatic Tertiary Deposits Called Holset Sands, and of Related Sands in Belgium”. Netherlands Journal of Geosciences (January 1, 1983): 431-436. Accessed April 2, 2026. https://njgjournal.nl/index.php/njg/article/view/13404.