Neptunism
obsolete theory that rocks formed from the crystallisation of minerals in the early Earth’s oceans, through processes such as great floods
Neptunism is a scientific theory of geology proposed by Abraham Gottlob Werner (1749–1817) in the late 18th century.
It proposed that rocks formed from the crystallisation of minerals in the early Earth's oceans. That is why it is called neptunism, because Neptune was the old Roman God of the sea.
There are many many different types of rock formation. Sedimentary rock is formed by processes very similar to neptunism. Basically, it makes rock out of bits of earlier rock and organisms.