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:
Type Area  Shores and hillslopes around Grudie, Durness area, north coast of Scotland. Peach et al., 1907; Prigmore and Rushton, 1999. 
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. 
Reference(s):
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. Geolgical 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. 
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.) 
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. 
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.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S114 S071 S107 S108 S081 S101