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  Craig-y-Glyn, near Llanrhaiadr, Powys, Wales. 
Type Area  The Lwrch inlier in the valley of Afon Lwrch around Pen-y-graig. Wedd, C B et al. 1929. 
Reference(s):
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 Unpublished PhD thesis, Cambridge University. 
Cantrill,T C, and others. 1914. Denbighshire and Shropshire district. Summary of Progress of the Geological Survey of Great Britain, for 1914, p.7. 
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