The BGS Lexicon of Named Rock Units — Result Details

Foel Y Ddinas Mudstones Formation

Computer Code: FYD Preferred Map Code: Fyd
Status Code: Pending Upgrade
Age range: Hirnantian Age (OH) — Hirnantian Age (OH)
Lithological Description: Dark blue silty mudstones. Includes Calettwr Quartzite and Hirnant Limestone at the top of the formation.
Definition of Lower Boundary: Base succeeds grey siltstones, mudstones and thin sandstone laminae of the Moelfryn Mudstones.
Definition of Upper Boundary: Top - succeeded by striped dark-blue shales with subsidiary siltstones of the Cwm-yr-Aethnen Mudstones.
Thickness: 125 metres.
Geographical Limits: Not defined.
Parent Unit: Not Applicable (-)
Previous Name(s): Foel-Y-Ddinas Mudstones [Obsolete Name And Code: Use FYD] (FDMA)
Foel Y Ddinas Mudstones (-3411)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Bala, Sheet 136. 
Reference(s):
Bassett, D A, Whittington, H B and Williams, A. 1966. The stratigraphy of the Bala district, Merionethshire. Quarterly Journal of the Geological Society of London, Vol.122, 219-271. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120 E136