- Sill
- Silurian Period
- Sinkholes
- Slate
- Slump
- Smith, William (1769-1839)
- Smog
- Soil and Soil Horizons
- Solar Energy
- Solar Illumination: Seasonal and Diurnal Patterns
- Solar Sunspot Cycle
- Solar System
- Solid Solution Series
- Solomon, Susan (1956- )
- Sorosilicates
- Sound Transmission
- South America
- Space
- Space and Planetary Geology
- Space Physiology
- Space Probe
- Space Shuttle
- Spacecraft, Manned
- Spectroscopy
- Springs
- Stalactites and Stalagmites
- Stellar Evolution
- Stellar Life Cycle
- Stellar Magnitudes
- Steno, Nicolas (1638-1686)
