The BGS Lexicon of Named Rock Units — Result Details

Crom Psammite Formation

Computer Code: CMPS Preferred Map Code: SYMB
Status Code: Full
Age range: Proterozoic Eon (AP) — Proterozoic Eon (AP)
Lithological Description: Well-bedded, flaggy to massive, white to pale grey and buff psammite, with abundant sedimentary structures. Garnetiferous semipelite bands are common in the lower portion, and it is locally pebbly in the upper part.
Definition of Lower Boundary: Overlies the Vach Pelite Formation, where predominantly pelitic lithologies pass into predominaintly psammitic lithologies.
Definition of Upper Boundary: Overlain by the Diebidale Pelite Formation, where predominainlty psammitic lithologies pass into predominantly pelitic lithologies. The upper boundary is locally obscured by the Sgurr Beag Thrust, the Carn Chunneag-Inchbae Granite Gneiss, or the Old Red Sandstone unconformity.
Thickness: Not recorded.
Geographical Limits: Comprises a large outcrop north of Loch Luichart, around the Carn Chuinneag intrusion, beneath large areas of Strathgarve Forest, Gabat Forest, Wyvis Forest, and the area around Loch Vaich and Gleann Mor. The north-eastern margin is defined by the faulted Old Red Sandstone unconformity, trending north-east from Loch Fleet in the north-east, to Strathglass in the south-west. It may continue to the north, on the eastern side of the Rogart Pluton at the western end of Strath Bora. The extent to the north and west of the Rogart Pluton is unclear. The eastern limit is largely defined by the Sgurr Beag Thrust running north-east to south-west from Loch Luichart (NH360620) to Dornoch Firth (NH645875). South of Loch Luichart the south-eastern extent is constrained by the Strathconnon Fault. The southern boundary is constrained by the Sgurr Beag Thrust occurring in the area from Sgurr a'
Parent Unit: Morar Group (MORR)
Previous Name(s): Upper Quartzite (-1447)
Upper Psammite (-4558)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  Southern and eastern flanks of Meall a' Chuaille, at the head of Strath Vaich (Tollomuick Forest). 
Reference(s):
Shepherd, J. 1970. The structure and metamorphism of the Carn Chuinneag area, Ross-shire. (University of Edinburgh.: unpublished PhD thesis.) 
Holdsworth, R E, Strachan, R A and Harris, A L, 1994. Precambrian rocks in northern Scotland east of the Moine Thrust: The Moine Supergroup in Gibbons, W and Harris, A L (editors). A revised correlation of Precambrian rocks in the British Isles. Special Report of the Geological Society, No.22. 
Wilson, D. 1975. Structure and metamorphism of the Ben Wyvis District, Ross-shire. (University of Edinburgh: Unpublished PhD thesis.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S083 S093 S093 S093