South Stack Formation

The South Stack Formation is a sequence of Cambro-Ordovician (Furongian to Tremadocian) metasedimentary rocks exposed in northwestern Anglesey, North Wales.^[1] 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.^[2]

Closer view of the rock formation

South Stack Formation
Stratigraphic range: Furongian-Tremadoc ~497–477 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Folded metamorphosed sandstones of the South Stack Formation
Type	Geological formation
Unit of	Holy Island Group
Underlies	New Harbour Group
Overlies	not exposed
Thickness	~360–1,000 m (1,180–3,280 ft)
Lithology
Primary	Metamorphosed sandstone
Other	Metamorphosed mudstone
Location
Coordinates	53°18′N 4°41′W
Region	Holy Island, Anglesey
Country	Wales
Type section
Named for	South Stack
South Stack Formation (the United Kingdom) Show map of the United Kingdom South Stack Formation (Wales) Show map of Wales