What was the main concept behind James hutton's theory?

James Hutton

1 Jan 1785

Used Steno's Law of Superposition. It compares rock layers to rocks above and below the rock. Evidence: Hutton found granite penetrating metaphoric schists, in a way which indicated that the granite had been molten at the time. This showed to him that granite formed from cooling of molten rock, not precipitation out of water as others at the time believed, and that the granite must be younger than the schists.