Plutonic theory's the geologic theory proposed by James Hutton around the turn of the 19th century that volcanic activity was the source of rocks on the surface of the Earth with forms we see today only arising after erosion or other gradual processes. It was named for Pluto, the ancient Roman god of the underworld. This replaced Abraham Werner's Neptunism theory, which claimed that rocks had originated from a great flood and were basically sedimentary in origin.… (More on Plutonism)