The BGS Lexicon of Named Rock Units — Result Details
Ffestiniog Flags Formation
| Computer Code: | FF | Preferred Map Code: | Ff |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | Merioneth Series (EM) — Merioneth Series (EM) | ||
| Lithological Description: | Regular alternatives of quartzose siltstone and sandstone in beds up to 2m thick, interbedded with silty mudstone; abundant sedimentary structures. | ||
| Definition of Lower Boundary: | Conformable and transitional, with the Maentwrog Formation. Marked by change in colour from pale to dark grey in mudstones, and an increase in sandstone. | ||
| Definition of Upper Boundary: | Conformably overlain by mudstones of the Dolgellau Formation. Sharp contact locally. | ||
| Thickness: | 475 to 1020m | ||
| Geographical Limits: | Northern, eastern and southern flanks of the Harlech Dome, North Wales. | ||
| Parent Unit: | Mawddach Group (MWG) | ||
| Previous Name(s): | Ffestiniog Group [Obsolete Name and Code: Use FF]
(-2182)
Lingula Flags [Obsolete Name And Code: Use LF] (LFS) Ffestiniog Formation [Obsolete Name And Code: Use FF] (FFB) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Reference Section | Cliffs immediately east and west of Portmeirion. Howells, M F and Smith, M. 1997. | ||
| Reference Section | North of Morfa Bychan. | ||
| Type Section | Bryn-Y-Gath, Upper Mawddach Valley. | ||
| Reference Section | Foreshore of Borth-y-gest, Porthmadog. Howells, M F and Smith, M. 1997. | ||
| Reference(s): | |||
| Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 (England and Wales). (London: HMSO.) 112 pp. | |||
| Ramsay, A C. 1866. The geology of North Wales. Memoir of the Geological Survey of Great Britain, Vol.3, | |||
| Howells, M F and Smith, M. 1997. Geology of the country around Snowdon. Memoir of the British Geological Survey, Sheet 119 (England and Wales). (London: The Stationery Office). 104pp. | |||
| Ramsay, A C, Salter, J W and Etheridge, R. 1881. The geology of North Wales. Memoir of the Geological Survey of Great Britain (2nd edition). No 3. [London: HMSO.] 611pp. | |||
| Allen, P M, Jackson, A A, and Rushton, A W A. 1981. The stratigraphy of the Mawddach Group in the Cambrian succession of North Wales. Proceedings of the Yorkshire Geological Society, Vol. 43, 295-329. | |||
| Belt, T. 1867. On the "Lingula Flags" or "Ffestiniog Group" of the Dolgelly District. Parts I and II. Gelogical Magazine, Vol. 4, 493-495, 536-543. | |||
| Belt, T. 1868. On the "Lingula Flags" or "Ffestiniog Group" of the Dolgelly District. Part III. Gelogical Magazine, Vol. 5, 5-11. | |||
| Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). | |||
| Waters, C N, Smith, K, Hopson, P M, Wilson, D, Bridge, D M, Carney, J N, Cooper, A H, Crofts, R G, Ellison, R A, Mathers, S J, Moorlock, B S P, Scrivener, R C, McMillan, A A, Ambrose, K, Barclay, W J, and Barron, A J M. 2007. Stratigraphical Chart of the United Kingdom: Southern Britain. British Geological Survey, 1 poster. | |||
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
| E119 E135 E149 E134 | |||