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- Thomas Jaggar (1871-1953), USA, volcanologist and founder of the Hawaiian Volcano Observatory.
- James A. Jensen (1911–1998), USA, distinguished dinosaur paleontologist and sculptor
- Dougal Jerram (1969– ), UK British geologist/earth scientist, television and media presenter and author
- David A. Johnston (1949–1980), USA, volcanologist, killed in the 1980 eruption of Mount St. Helens
- Franc Joubin (1911–1997), Canada (born USA), discovered Elliot Lake uranium district
Read more about this topic: List Of Geologists