:South Stack Formation

{{short description|Cambro-Ordovician geologic formation in Wales}}

{{Use dmy dates|date=April 2022}}

{{Infobox rockunit

| name = South Stack Formation

| image = Sea cliff at South Stack - geograph.org.uk - 113500.jpg

| caption = Folded metamorphosed sandstones of the South Stack Formation

| type = Geological formation

| age = Furongian-Tremadoc
~{{fossil range|497|477}}

| period = Furongian

| prilithology = Metamorphosed sandstone

| otherlithology = Metamorphosed mudstone

| namedfor = South Stack

| namedby =

| region = Holy Island, Anglesey

| country = Wales

| coordinates = {{coord|53|18|N|4|41|W|display=inline,title}}

| unitof = Holy Island Group

| subunits =

| underlies = New Harbour Group

| overlies = not exposed

| thickness = ~{{convert|360|-|1000|m|ft|abbr=on}}

| extent =

| area =

| map = {{Location map+ | United Kingdom#Wales

| relief = 1

| width = 250

| float = center

| places =

{{Location map~ | United Kingdom#Wales

| lat_deg = 53.3

| lon_deg = -4.6

| mark = SpringGreen pog.svg

| marksize = 12

}}

}}

| map_caption =

}}

The South Stack Formation is a sequence of Cambro-Ordovician (Furongian to Tremadocian) metasedimentary rocks exposed in northwestern Anglesey, North Wales.{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=NSS | title=South Stack Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=13 October 2014}} The outcrop of this formation at South Stack was chosen as one of the top 100 geosites in the United Kingdom by the Geological Society of London, for its display of small-scale folding.{{cite web | url=http://apps.esriuk.com/app/GreatGeosites/3/wmt/view/5e0d44970b3a4b4dafb7da0404b2d8ed/index.html | title=The Geological Society's 100 Great Geosites | publisher=The Geological Society | date=2014 | accessdate=14 October 2014}}

File:Detail of 'South Stack Formation' - a geological term for the cliff face at Ynys Lawd (South Stack) 09.jpg