From 1929 he went back to Leiden to become the assistant of his former teacher B.G. Escher. In 1930 he became professor in stratigraphy and paleontology at Delft University. His research was again multidiciplinary. He studied the paleogeography of the Dutch East Indies from the data acquired by the gravitational surveys of F.A. Vening Meinesz, the paleontology of corals and coral reefs, tectonics, the geology of the Netherlands and volcanology. Because of his broad field of interest he was one of the first to think of the Earth as one dynamic system, an idea on which he wrote his book the Pulse of the Earth in 1942. Another book on paleontology was published in 1943.
When he turned seriously ill in 1952 he kept writing in his bed, until his death in 1954.