Hutton did not describe the Earth’s evolution as a linear and irreversible process but as a dynamic cycle of erosion, deposition, consolidation, and uplifting before erosion starts the cycle anew. At localities in Scotland, he observed that granite was not the oldest rock, as Werner and his student Johann Wolfgang von Goethe had assumed. Underneath the granite were deep vertical strata of slate, which were much older. These conclusions were presented in a powerful illustration that adorned the second edition of Hutton’s Theory of the Earth. Underneath the familiar horizontal line depicting the Earth’s surface, the slate deposits plunge into the depths, exceeding by far the strata lying above them. [..] This discovery must have been as stunning and important for geology as were the first depictions of the Copernican view of the solar system, which firmly dislodged the Earth from the centre of the universe.
Siegfried Zielinski, Deep Time of the Media, 5.
I think this is the illustration/diagram Zielinski is talking about but I could be wrong. Chime in if you think I am wrong!