The BGS Lexicon of Named Rock Units — Result Details

Hollin Rock

Computer Code: HLR Preferred Map Code: notEntered
Status Code: Index Level
Age range: Bolsovian Substage (CC) — Bolsovian Substage (CC)
Lithological Description: Fine to coarse or pebbly, commonly feldspathic, cross laminated and channel bedded sandstone. The base often channels into the beds below. The sandstone is locally interbedded with thin mudstones. The Hollin Rock Member represeents a widespread deltic sandstone body, or series of bodies, within the Flintshire Coalfield, and may record a period of distributary channel and mouth bar advances at a time of lowered sea level.
Definition of Lower Boundary: The type section displays a sharp base of grey sandstone overlying dark mudstones with ironstones, about 4.44m above top of Massy (Drowsell) Coal (J500 of British Coal). Elsewhere the base channels down in places to below the Hollin Coal (H800 of British Coal).
Definition of Upper Boundary: The type section shows a sharp contact between hard, white sandstone and overlying seat earth (fireclay), about 3 m below base of the Etruria Formation.
Thickness: Up to 75 thick.
Geographical Limits: The Flintshire Coalfield (SJ 27 68), north-east Wales.
Parent Unit: Pennine Middle Coal Measures Formation (PMCM)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Borehole by Northophall Colliery Company, SJ26NE/1317 -see Wedd and King (Flint Memoir) 1924, p.109. Base at 110.03 m; top at 34.47 m as recorded in the borehole log. Strahan, 1890. 
Reference(s):
Wedd, C B and King W B R. 1924. Geology of the country around Flint, Hawarden and Caergwrle. Memoir of the Geological Survey of Great Britain, Sheet 108, p.109. 
Strahan, A, 1890. The Geology of the Neighbourhoods of Flint, Mold and Ruthin. Memoir of the Geological Survey, Sheet 79SE (England and Wales). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E108