The BGS Lexicon of Named Rock Units — Result Details

Craig-Y-Glyn Formation

Computer Code: CGYG Preferred Map Code: CgF
Status Code: Full
Age range: Caradoc Series (O4) — Caradoc Series (O4)
Lithological Description: Calcareous mudstones. (Well stratified rhyolitic and calcareous ash, and pale blue bedded limestone; with calcareous shale and calcareous, blue mudstone and shale).
Definition of Lower Boundary: Not seen.
Definition of Upper Boundary: In faulted contact with mudstones of Llangynog Formation of Carodocian age.
Thickness: Greater than 300m in the Lwrch inlier.
Geographical Limits: Limited to fault bounded inliers in the central Berwyn Hills, Lwrch inlier (137), Llwyn-Onn inlier (136) (ca SJ 073 264), Garwallt inlier (136) (ca SJ 091 281).
Parent Unit: Not Applicable (-)
Previous Name(s): Craig-Y-Glyn Group (-2078)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Lwrch inlier in the valley of Afon Lwrch around Pen-y-graig. Wedd, C B et al. 1929. 
Type Area  Craig-y-Glyn, near Llanrhaiadr, Powys, Wales. 
Reference(s):
Cantrill,T C, and others. 1914. Denbighshire and Shropshire district. Summary of Progress of the Geological Survey of Great Britain, for 1914, p.7. 
MacGregor,A R. 1958. The Llandeilo limestone of the Central Berwyns and a comparison with rocks of the same age in north-western Europe. Unpublished PhD thesis, Cambridge University. 
Wedd, C B, Smith, B, King, W B R and Wray, D A. 1929. Geology of the country around Oswestry. Memoir of the Geological Survey of Great Britain, Sheet 137. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E136 E137