the Glen Tilt of Perthshire as they were intruded through Dalradian metasediments, indicated by the cut across sediment layers. This indicated to Hutton that the sediments were older than the granite. This contradicted Neptunism, as it believes granites to be precipitated out of the ocean, hence being the oldest rock type.

In 1773, prior to Hutton's observations, Abraham Gottlob Werner published his mineralogy