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, but the term is used to describe any break in the
sedimentary geologic record. The significance of angular unconformity (see below) was shown by
James Hutton, who found examples of
Hutton's Unconformity at
Jedburgh in 1787 and at
Siccar Point in 1788.