Plutonism

Plutonism (or Vulcanism) is the theory that the rocks forming the Earth were formed in fire by volcanic activity.
It was named after Pluto, the classical ruler of the underworld, or alternatively after Vulcan, the ancient Roman god of fire and volcanoes. The theory was first proposed by Abbé Anton Moro who had studied volcanic islands. It was subsequently developed by James Hutton as part of his "Theory of the Earth" published in 1788. 
The Plutonists strongly disputed the Neptunist view that rocks had been formed by processes that no longer operated, instead supporting Hutton's uniformitarianism.