Definition of "plutonist"

The Plutonists, who had Thomas Huxley on their side, asserted that rocks such as basalt and granite, which originated in a molten state deep within the Earth, were the primary source, and that the other rock types such as sandstone and slate were formed from their breakdown and re-deposition as silt and mud.

2018, Tim Flannery, Europe: A Natural History, page 74