noun
neptunism
Geological term for the 18th-century theory that all rocks formed by crystallization from a primordial ocean. Now only of historical interest.
水成論は、かつて岩石の起源を説明する有力な学説だった。
Neptunism was once a prominent theory explaining the origin of rocks.
火成論 (plutonism) is the opposing theory that rocks formed by volcanic heat, historically contrasted with 水成論.
From 水成 (suisei, 'formed by water') + 論 (ron, 'theory'). The term is a direct calque of German 'Neptunismus', coined in the late 18th century.