Editing Unconformity (section)

{{Short description|Rock surface indicating a gap in the geological record}}
[[File:Hutton Unconformity , Jedburgh.jpg|thumb|''[[Hutton's Unconformity]]'' at [[Jedburgh]], [[Scotland]], illustrated by [[John Clerk of Eldin|John Clerk]] in 1787 and photographed in 2003.]]
An '''unconformity''' is a buried [[erosion surface|erosional]] or non-depositional surface separating two [[Rock (geology)|rock]] masses or [[Stratum|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 rocks|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 [[Berwickshire]] in 1788, both in Scotland.<ref>[http://www.snh.org.uk/publications/on-line/geology/elothian_borders/hutton.asp Hutton's Unconformity] {{Webarchive|url=https://web.archive.org/web/20150924104617/http://www.snh.org.uk/publications/on-line/geology/elothian_borders/hutton.asp |date=2015-09-24 }}</ref><ref name=monty>{{cite web |url=http://nagt.org/files/nagt/jge/abstracts/Montgomery_v51n5.pdf |title=Siccar Point and Teaching the History of Geology |access-date=2015-03-16 |author=Keith Montgomery |year=2003 |publisher=University of Wisconsin }}</ref>

The rocks above an unconformity [[Law of superposition|are younger than]] the rocks beneath (unless the sequence has been overturned). An unconformity represents [[Geologic time|time]] during which no sediments were preserved in a region or were subsequently eroded before the next deposition. The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area.  The interval of geologic time not represented is called a '''hiatus'''. It is a kind of [[relative dating]].