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- Donald F. Sangster, Canada, lead-zinc economic geologist
- Manuel Santillán (1894–1982), Mexican geological engineer and politician
- Harrison Schmitt (born 1935), USA, Apollo 17 moonwalker
- Adam Sedgwick (1785–1873), England, proposed Devonian and Cambrian periods
- Seikei Sekiya (1855–1896), Japanese seismologist, created the model showing the motion of an earth-particle during an earthquake
- Nicholas Shackleton (1937–2006), British geologist and climatologist
- Shen Kuo (1031–1095), Chinese scientist, magnetic compass pioneer, geomorphology theory
- Eugene Merle Shoemaker (1928–1997), USA, meteoriticist, co-discovered Comet Shoemaker-Levy
- Haraldur Sigurdsson, (born 1939), Iceland, provided proof for a meteorite impact at the time of the extinction of the dinosaurs
- George Gaylord Simpson (1902–1984), USA, paleontologist
- William Smith (1769–1839), father of English Geology
- Su Song (1020–1101), Chinese naturalist, author of treatise on metallurgy and mineralogy
- Josiah Edward Spurr (1870–1950), USA, geologist, author and Alaskan explorer
- Flaxman Charles John Spurrell (1842–1915), English archaeologist, geologist and photographer
- Charles Steen (1919–2006), USA, discovered uranium near Moab, Utah
- Max Steineke (died 1952), USA, credited with the discovery of oil in Saudi Arabia in the 1930s
- Charles R. Stelck (born 1917), Canada, petroleum geologist, emeritus professor
- Nicolas Steno (1638–1686), Denmark, pioneer in early-modern geology
- Iain Stewart (born 1964), UK, presenter of several television series on geology in the UK.
- Clifford H. Stockwell (1897–1987), Canadian structural geologist, Geological Survey of Canada
- David Strangway, Canada, geophysicist and university administrator
- Eduard Suess (1831–1914), Austria (born England), named Gondwanaland
- Peter Szatmari Hungarian–Brazilian geologist
Read more about this topic: List Of Geologists