The BGS Lexicon of Named Rock Units — Result Details

Hillhead Sandstone Formation

Computer Code: HSA Preferred Map Code: Has
Status Code: Full
Age range: Eifelian Age (DI) — Eifelian Age (DI)
Lithological Description: A red and grey, planar-bedded, quartzose, sandstone with interbeds of micaceous siltstone and silty mudstone.
Definition of Lower Boundary: Conformable on the Ishes Flagstone Formation. At its type site, the base is taken as a gradual facies change from grey calcareous, laminated fine-grained flaggy sandstone of the Ishes Flagstone, to a red coarser-grained sandstone.
Definition of Upper Boundary: Overlain unconformably by red flaggy sandstone of the Nairn Sandstone Formation.
Thickness: Up to 920 m thick.
Geographical Limits: Sheet S84W (Fortrose).
Parent Unit: Inverness Sandstone Group (INS)
Previous Name(s): Hillhead Sandstones, Flagstones And Shales (-4101)
Hillhead Group (-966)
Hillhead Red Bed Subgroup [Obsolete Name And Code: Use HSA] (HRB)
Alternative Name(s): none recorded or not applicable
Partial Type Section  Hillhead Quarry, about 100 m south of Hillhead Farm, about 6 km northeast of Smithton, showing only a small proportion of the middle part of the unit, of which some 4 m are exposed. 
Partial Type Section  Leys-Culduthel Quarry on the soutwest side of General Wade's Military Road, about 0.7 km southwest of the outskirts of Inverness. Shows the basal part of the unit only. 
Mykura, W. 1991. Old Red Sandstone. 297-346 in Geology of Scotland (3rd edition, revised). Craig, G Y (editor). Geological Society of London. 
Fletcher, T P et al. 1996. Geology of the Fortrose and eastern Inverness district. Memoir of the British Geological Survey, Sheet 84W (Scotland). 
Horne, J, 1923. The geology of the Lower Findhorn and Lower Strath Nairn. Mmemoir of the Geological Survey of Scotland Sheet 84 and prt of 94. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: