| Computer Code: |
FFV |
Preferred Map Code: |
FFV |
| Status Code: |
Full |
| Age range: |
Caradoc Series (O4)
— Caradoc Series (O4) |
| Lithological Description: |
Trachyandesite lavas, tuffs and intrusions. Tuffs may be reworked, massive and welded, or bedded and unwelded. |
| Definition of Lower Boundary: |
Overlies mudstones of the Nant Ffrancon Subgroup and locally on the Foel Grach Basalt and Braich Tu Du Formation. Interdigitates with the Conwy Rhyolite Formation. |
| Definition of Upper Boundary: |
Underlies siltstones of the Nant Ffrancon Subgroup. |
| Thickness: |
About 1000m. Outflow much thinner, of the order 100m. |
| Geographical Limits: |
Foel Fras (8km west-north-west of Dolgarrog), south-west to Nant Ffrancon. |
| Parent Unit: |
Llewelyn Volcanic Group (LLV)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
Foel Fras hill and Bera Bach. |
| Reference(s): |
| Howells, M F, Reedman, A J and Campbell, S D G, 1991. Ordovician (Caradoc) marginal basin volcanism in Snowdonia (north-west Wales). (London: HMSO for the British Geological Survey). |
| Howells, M F, Leveridge, B E, Addison, R and Reedman, A J. 1983. The lithostratigraphical division of the Ordovician underlying the Snowdon and Crafnant volcanic groups, North Wales. Report of the Institute of Geological Sciences, No. 83/1. |
| Howells M F, Reedman A J and Leveridge B E. 1985. Geology of the country around Bangor: Explanation for 1:50 000 geological sheet 106 (England and Wales). British Geological Survey Sheet Explanation. [London: HMSO.] 34pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E106
|
