De Sitter studied geology in
Switzerland and later at
Leiden, where he was a pupil of geologists
Karl Martin (1851–1942) and
Berend George Escher (1885–1967). He finished his
dissertation in 1925 and then got a job at the
Bataafsche Petroleum Maatschappij. After some years, he returned to Leiden to become Escher's assistant. De Sitter's task was to supervise fieldwork and research in the
Bergamo Alps (northern Italy). In addition to mapping geological structures, De Sitter also did experimental research on the development and origin of geological structures such as
faults or
folds. He worked together on these experiments with
Philip Henry Kuenen, an old friend from his student days who would later become a professor at
Groningen. The
Second World War made research outside the Netherlands impossible for Dutch geologists. De Sitter and mining engineer
W.A.J.M. van Waterschoot van der Gracht organised field studies of the subsurface of the southeastern part of the Netherlands. The students who participated were in this way excluded from
forced labour for the
Nazi authorities. De Sitter started a geologic research program in the Pyrenees and
Cantabria (both in northern Spain) after the war. The geological surveys by the Leiden students are in some cases still used by the Spanish geologic survey. De Sitter became a professor in 1948. His further research was mainly on similarities and relations between different small-scale geologic structures (such as
boudins,
schistocities or
parasitary folds) and large-scale structures (such as folds and
thrusts up to the scale of mountain ranges). His book
Structural Geology was translated into many languages and used worldwide. In his later years at Leiden, his health prevented him from doing more field research, thus reducing his motivation. His method of putting all geologic observations into one large framework would be characteristic for the Leiden school of structural geology, which was continued under
Henk Zwart after De Sitter's retirement in 1968. In 1962, he became a member of the
Royal Netherlands Academy of Arts and Sciences. ==Selected publications==