The BGS Lexicon of Named Rock Units — Result Details

Ghrudaidh Formation

Computer Code: GUD Preferred Map Code: notEntered
Status Code: Full
Age range: Comley Series (EC) — Comley Series (EC)
Lithological Description: Dark to mid-grey dolostones containing burrow mottling, oolitic and bioclastic grainstones and rare stromatolites.
Definition of Lower Boundary: Conformably overlies the Salterella Grit Member of the An T'Sron Formation. The boundary is gradational over about a metre.
Definition of Upper Boundary: Conformably overlain by pale grey and buff flaggy dolostones of the Eilean Dubh Formation. A zone of interbedded dark and pale grey dolostones occurs at the boundary. The actual contact with the Eilean Dubh Formation is taken at the appearance of laminations and/or chert layers.
Thickness: From 50 m to 60 m thick.
Geographical Limits: The Durness Group , including the Ghrudaidh Formation, forms a narrow, discontinuous belt, extending along the north-western side of Scotland from the Durness-Eriboll area, through Assynt and Kishorn, to Skye.
Parent Unit: Durness Group (DNG)
Previous Name(s): Ghrudaidh Formation [Also Grudaidh Formation] [Obsolete Code: Use GUD] (GRU)
Ghrudaidh Group (-3448)
Alternative Name(s): Grudaidh Formation
Stratotypes:
Reference Section  Good exposures of the Ghrudaidh Formation occur near Skaig Bridge, Loch Assynt, and around Inchnadamph and the Stronchrubie cliffs. The grid ref. Below is for a section near Skaig Bridge which shows the lower boundary. Peach et al. , 1907. 
Type Area  Shores and hillslopes around Grudie, Durness area, north coast of Scotland. Peach et al., 1907; Prigmore and Rushton, 1999. 
Reference(s):
Johnston, G S and Mykura, W. 1989. British regional geology: the Northern Highlands (4th edition) (London: HMSO for the British Geological Survey.) 
Prigmore, J K and Rushton, A W A. 1999. Scotland: Cambrian and Ordovician of the Hebridean Terrane. 295-315 in British Cambrian to Ordovician Stratigraphy. Rushton, A W A, Owen, A W, Owens, R M and Prigmore, J K (editors). Geological Conservation Review Series. (Joint Nature Conservation Committee.) 
Cowie, J W. 1974. The Cambrian of Spitsbergen and Scotland. 123-155 in Cambrian of the British Isles, Norden and Spitsbergen, Holland, C H (editor). Lower Palaeozoic Rocks of the World, Vol. 2. (John Wiley and Sons.) 
Peach, B N, Home, J, Gunn, W, Clough, C T and Hinxman, L W, 1907. The Geological Structure of the northwest Highlands of Scotland. Memoir of the Geological Survey of Great Britain. 
Huselbee, M Y, and Thomas, A T. 1998. Olenellus and conodonts from the Durness Group, NW Scotland, and the correlation of the Durness succession. Scottish Journal of Geology, Vol. 34, 83-85. 
Lapworth, C. 1883. The secret of the Highlands. Geological Magazine, Decade 2, Vol. 10, 120-128, 193-199, 337-344. 
Park, E G, Stewart, A D and Wright, D T. 2002. The Hebredean Terrane. 45-80 in the Geology of Scotland. Trewin, N H (Editor). (The Geological Society, London.) 
Phemister, J. 1948. British Regional Geology: Scotland: the Northern Highlands (2nd edition) (Edinburgh: HSMO for the Geological Survey and Museum.) 
Wright, D T and Knight, I. 1995. A revised chronostratigraphy for the lower Durness Group. Scottish Journal of Geology, Vol. 31, 11-22. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S071 S107 S108 S081 S101 S114