The BGS Lexicon of Named Rock Units — Result Details

Meall Dubh Graphitic Schist Formation

Computer Code: MEDS Preferred Map Code: MeDG
Status Code: Full
Age range: Neoproterozoic Era (AZ) — Neoproterozoic Era (AZ)
Lithological Description: Graphitic pelite with semipelite ribs, containing porphyroblasts of kyanite (up to 100mm), biotite, garnet and rare staurolite and albite.
Definition of Lower Boundary: Gradational boundary with the Meall Dubh Limestone Formation with admixture of graphitic and calc-schists is poorly exposed.
Definition of Upper Boundary: Graphitic kyanite-bearing semipelite merges with 1m of transitional muscovitic, rusty-weathering quartzite with graphitic seams which forms the base of the Meall Dubh Quartzite Formation. This transitional quartzite is possibly equivalent to the Beinn a'Ghlo Transition of Smith, R A and Harris, A L (1976).
Thickness: 0 - 50m in Sheet 55W; much tectonic thinning compared with Beinn a' Ghlo Graphitic Schist/Ballachulish Slate.
Geographical Limits: Main development in Strath Fionan [NN 7257 7556]. Also occurs sporadically as far west as Allt na Moine Buidhe [NN 708 612] and as far east as Allt Kynachan [NN 7790 5725]. Not present east of the Loch Tay Fault, where its place is taken by the Beinn a'Ghlo Graphitic Schist Formation; some of the 'Banvie Burn Series' may be equivalent.
Parent Unit: Ballachulish Subgroup (DABH)
Previous Name(s): Ballachulish Slate (*559)
Beinn A'Ghlo Graphitic Schist (*922)
Meall Dubh Graphitic Schist (-4788)
Alternative Name(s): Beinn A'Ghlo Graphitic Schist
Ballachulish Slate
Stratotypes:
Type Section  Crag on north side of road through Strath Fionan, c.1km west-north-west of Braes of Foss. 
Reference(s):
Smith, R A and Harris, A L, 1976. The Ballachulish rocks of the Blair Atholl district. Scottish Journal of Geology, Vol.12, 153-157. 
Treagus, J E and King, G, 1978. A complete Lower Dalradian succession in the Schiehallion district, central Perthshire. Scottish Journal of Geology, Vol.14, 157-166. 
Treagus, J E. 2001. Solid geology of the Schiehallion district. Memoir of the British Geological Survey, Sheet 55W (Scotland). 
Harris, A L, Haselock, P J, Kennedy, M J and Mendum, J R, 1994. The Dalradian Supergroup in Scotland, Shetland and Ireland. 33-53 in Gibbons, W E and Harris, A L (editors). A revised correlation of Precambrian rocks in the British Isles. Special Report of the Geological Society, London, No.22. 
Stephenson, D and Gould, D , 1995. British Regional Geology: the Grampian Highlands (4th edition). (London: HMSO for the British Geological Survey), 67-68. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S055