Listed below are the letters and titles of the main classes of the Library of Congress Classification Outline.
G - Geography, Anthropology, Recreation
GB 3-5030 - Physical Geography
GB 400 - Geomorphology. Landforms
GB400-649 - Geomorphology. Landforms. Terrain
GB447 - Climatic geomorphology
GB448 - Slopes
GB450-460 - Coasts
GB461-468.995 - Reefs
GB471-478.995 - Islands
GB500-555 - Mountains. Orography
GB561-649 - Other natural landforms: Floodplains, caves, deserts, dunes, etc.
GB651-2998 - Hydrology. Water
GB980-2998 - Ground and surface waters
GB980-992 - Watersheds. Runoff. Drainage
GB1001-1199.8 - Groundwater. Hydrogeology
GB1201-1598 - Rivers. Stream measurements
GB1601-2398 - Lakes. Limnology. Ponds. Lagoons
GB2401-2598 - Ice. Glaciers. Ice sheets. Sea ice
GB2601-2798 - Snow. Snow surveys
GB2801-2998 - Hydrometeorology
GB5000-5030 - Natural disasters