The BGS Lexicon of Named Rock Units — Result Details

Cwm-Yr-Hob Member

Computer Code: CYH Preferred Map Code: CYH
Status Code: Full
Age range: Ludlow Epoch (SU) — Ludlow Epoch (SU)
Lithological Description: Interlaminated and very thinly interbedded grey silty mudstone, siltstone/fine-grained sandstone and carbonaceous (anoxic) hemipelagite; disruptive bioturbation negligible.
Definition of Lower Boundary: Disappearance of thick mudstone turbidite units of underlying undifferentiated Bailey Hill Formation.
Definition of Upper Boundary: First appearance of significant disruptive bioturbation, indicating onset of oxic bottom conditions.
Thickness: Up to 220m thick.
Geographical Limits: Dies out southwards; southern limit at c. (SO 158 795); northwards extends at least as far as (SO 120 850).
Parent Unit: Bailey Hill Formation (BAI)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Approximately Equivalent To The Monograptus Leintwardinensis Shales.
Stratotypes:
Reference Section  Lyrychyn Quarry, Cilfaesty Hill. 
Type Section  Track section north-east of the old (now abandoned) Cwm-yr-hob farmhouse, Felindre, Powys. 
Reference(s):
Earp, J R, 1938. The higher Silurian rocks of the Kerry district, Montgomeryshire. Quarterly Journal of the Geological Society of London. Vol.94/1, p.125-160. 
Cave, R and Hains, B A. 2001. Geology of the country around Montgomery. Memoir of the British Geological Survey, Sheet 165 with part of 151 (Welshpool) (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E165