| Computer Code: |
PGT |
Preferred Map Code: |
Pngr |
| Status Code: |
Full |
| Age range: |
Longvillian Substage (OL)
— Longvillian Substage (OL) |
| Lithological Description: |
Laterally discontinous acid tuff. (coarse ash of Wedd et al., 1929). |
| Definition of Lower Boundary: |
Base of tuff succeeds siltstones of the Bryn Siltstone Formation. |
| Definition of Upper Boundary: |
Uncomformably overlain by Ashgill, grey-green muds of the Dolhir Formation. |
| Thickness: |
To 7m |
| Geographical Limits: |
North side of Berwyn Hills of Oswestry (137) and Wrexham (121). Overstepped by Dolhir Formation. |
| Parent Unit: |
Bryn Siltstone Formation (BSI)
|
| Previous Name(s): |
Pen Y Graig Ash [Obsolete Name and Code: Use PGT]
(-1119)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Oswestry, Sheet 137. |
| Type Area |
Outcrops at Pen-y-graig. |
| Reference(s): |
| Brenchley, P J. 1978. The Caradocian rocks of the North and West Berwyn Hills. Geological Journal, Vol. 13, 137-164. |
| Wedd, C B, Smith, B, King, W B R and Wray, D A. 1929. Geology of the country around Oswestry. Memoir of the Geological Survey of Great Britain, Sheet 137. |
| Groom, T and Lake, P. 1908. The Bala and Llandovery rocks of Glyn Ceiriog (North Wales). Quarterly Journal of the Geological Society, Vol.64/4, p.546-595. |
| Brenchley, PJ. 1966. The Caradoc rocks of the north and west Berwyns, North Wales. Unpublished PhD thesis, University of Liverpool. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E120
E121
E137
|
