Classification
GCAC - Regional geology - noneuropean countries
4
GHF - Igneous rocks, metamorphic rocks
4
GBA - General geology, historical geology
2
GBAH - Stratigraphy, history of earth
2
GBAK - Paleontology
2
GBEN - Tectonics
2
GBER - Volcanism
2
GHA - Petrology - general
2
GMA - Geochemistry - general
2
GWCD - Ore mining, ore processing
2