An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger layer, but the term is used to describe any break in the sedimentary geologic record. The significance of angular unconformity was shown by James Hutton, who found examples of Hutton's Unconformity at Jedburgh in 1787 and at Siccar Point in Berwickshire in 1788, both in Scotland.
Hutton's Unconformity at Jedburgh, Scotland, illustrated by John Clerk in 1787 and photographed in 2003.
Disconformity
Nonconformity
Angular unconformity
James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the "Father of Modern Geology," he played a key role in establishing geology as a modern science.
Portrait by Henry Raeburn, 1776
Hutton's Unconformity on Arran
John Kay's caricature of James Hutton studying the "faces" of rock (1787)
Street sign in the Kings Buildings complex in Edinburgh to the memory of James Hutton