Geldern ya iku wong kang mapanake dhasar-dhasar prasajarah Indonésia bebarengan karo Von Stein Callenfels. Karya-karyané kang wis digawé ing antarané "Urheimat und fruheste Wanderungen des Austronesier" (Anthropos XXVII, 1932) lan "Prehistoric research in the Netherlands Indies"sajeroning: "Science and Scientists in the Netherlands Indies" (New York, 1945), "The Archaeology and Art of Sumatra", sajeroning "E. M. Loeb, Sumatra, Its History and People" (Vienna, 1935), "Some Problems of Migration in the Pacific" sajeroning "Kultur und Sprache" (diedit olèh W. Koppers, Vienna, 1952), "Research on Southeast Asia: Problems and Suggestions" sajeroning "American Anthropologist" (April, 1946).