South Stack Formation

South Stack Formation Stratigraphic range: Furongian-Tremadoc ~497–477 Ma PreЄ Є 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 / 53.3°N 4.683°W / 53.3; -4.683
Region	Holy Island, Anglesey
Country	Wales
Type section
Named for	South Stack
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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

References

Further reading

• Phillips, E, 1991. Progressive deformation of the South Stack and New Harbour Groups, Holy Island, Western Anglesey, North Wales. Quarterly Journal of the Geological Society, Vol.148, p. 1091-1100
• Shackleton, R M, 1954. The structure and succession of Anglesey and the Lleyn Peninsula. British Association for the Advancement of Science, Vol.11, p. 106-108
• Greenly, E. 1919. Geology of Anglesey. Memoir of the Geological Survey, UK
• Blake, J F, 1888. The Monian System of rocks. Quarterly Journal of the Geological Society, Vol.44, p. 476-480

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