| Computer Code: |
MAF |
Preferred Map Code: |
MaF |
| Status Code: |
Full |
| Age range: |
Merioneth Series (EM)
— Merioneth Series (EM) |
| Lithological Description: |
Grey siltstones and sandstones with rare ironstones near the base. Top marked by coarse-grained quartzose pebbly sandstone. |
| Definition of Lower Boundary: |
Conformable and gradational from mainly coarse-grained sandstones of the underlying Bronllwyd Grit Formation. |
| Definition of Upper Boundary: |
Unconformable upper contact with overlying late Cambrian,Tremadoc or basal Arenig strata, (Dolgellau, Dol-cyn-afon or Allt Llwyd formations). The base of the overlying Arenig is characterized locally by sandstones. |
| Thickness: |
240 to 500m |
| Geographical Limits: |
Northern Snowdonia and Arfon. |
| Parent Unit: |
Mawddach Group (MWG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Around Marchlyn Mawr, above Llanberis, North Wales. |
| Reference(s): |
| 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. |
| 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: |
|
E119
E106
|
