Editing Old Red Sandstone (section)

{{short description|Assemblage of rocks in the North Atlantic region}}
{{Globalize|1=article|2=United Kingdom|date=August 2024}}
{{Infobox rockunit
| name = Old Red Sandstone
| image = Folded_Old_Red_Sandstone_at_St_Annes_Head_-_geograph.org.uk_-_629204.jpg
| caption = Folded Old Red Sandstone rock formation at St Ann's Head in [[Pembrokeshire]], Wales
| type = [[Supergroup (geology)|Supergroup]]
| prilithology = [[Sandstone]]
| otherlithology = [[conglomerate (geology)|Conglomerate]], [[shale]], [[mudstone]], [[siltstone]], [[limestone]]
| namedfor = 
| namedby = 
| region = [[North Atlantic]]
| country = Canada, Greenland, Ireland, Norway, United Kingdom
| coordinates = 
| unitof = 
| subunits = ''See text''
| thickness = More than {{convert|4|km|mi|abbr=on}} (Shetland)
| extent = {{convert|700|km|mi|abbr=on}}<ref name="Barclay" />
| area = 
| age = [[Late Silurian]]{{snd}}earliest [[Carboniferous]] {{fossilrange|419|358}}
| period = Devonian
}}
[[File:Siccar point SE cliff.jpg|thumb|[[James Hutton|Hutton's]] [[Hutton's Unconformity|angular unconformity]] at [[Siccar Point]] where 370-million-year-old [[Devonian]] Old Red Sandstone overlies 435-million-year-old [[Silurian]] [[greywacke]].<ref name="FieldExcursion" />]]

'''Old Red Sandstone''', abbreviated '''ORS''', is an assemblage of rocks in the North Atlantic region largely of [[Devonian]] age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the eastern seaboard of [[North America]]. It also extends northwards into [[Greenland]] and [[Svalbard]].<ref>Friend, P.F. and Williams, B.P.J. (eds) 2000 ''New Perspectives on the Old Red Sandstone''. Geological Society, London, Special publications '''180''' p1,35</ref> These areas were a part of the [[paleocontinent]] of [[Euramerica]] (Laurussia). In Britain it is a [[lithostratigraphy|lithostratigraphic]] unit (a sequence of [[rock strata]]) to which [[Stratigraphy|stratigraphers]] accord [[Geological unit#Lithostratigraphic units|supergroup]] status<ref>http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=ORS entry in BGS on-line rock lexicon</ref> and which is of considerable importance to early [[paleontology]]. The presence of ''Old'' in the name is to distinguish the sequence from the younger [[New Red Sandstone]] which also occurs widely throughout Britain.