Hutton's Unconformity

Hutton's Unconformity is a name given to various notable geological sites in Scotland identified by the 18th-century Scottish geologist James Hutton as places where the junction between two types of rock formations can be seen. This geological phenomenon marks the location where rock formations created at different times and by different processes adjoin. For Hutton, such an unconformity provided evidence for his Plutonist theories of uniformitarianism and the age of Earth.

An unconformity is a break in the normal progression of sedimentary deposits, where newer deposits are laid on top of older. The example Hutton discovered is known as an angular unconformity in which a sharp change in younging direction can be seen in the orientation of bedding planes. The younging direction points from the oldest bed, to the youngest bed in the sequence of sedimentary beds.

In his search, Hutton and colleagues examined rock outcrops and cliffs, both riverside and sea, and found several locations where two adjoining rock types had been laid bare, the most noted being at Siccar Point on the coast of Berwickshire.