J.W.M. Jagt, E.A. Jagt-Yazykova, and W.J.H. Schins. “A Tribute to the Late Felder Brothers – Pioneers of Limburg Geology and Prehistoric Archaeology; Introduction”. Netherlands Journal of Geosciences 90 (November 1, 2011): 65 - 71. Accessed February 22, 2025. https://njgjournal.nl/index.php/njg/article/view/12042.