The BGS Lexicon of Named Rock Units — Result Details

Merion Till Member

Computer Code: MNTI Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Generally stiff, blue-grey, stony, sandy and silty clay and clayey gravel, characteristically containing Lower Palaeozoic clasts (derived from the Cambrian Mountains) with some erratics from Snowdon and the Harlech Dome. Subordinate stratified sand and gravel are locally present. Colour and dominant clast composition are variable and generally reflect the local bedrock geology.
Definition of Lower Boundary: Generally unconformable on bedrock or regolith/head (e.g. Hiraethog Member of Bowen 1999).
Definition of Upper Boundary: Generally the ground surface or unconformable contact with overlying peat, head, river terrace deposits or alluvium (Cheshire - North Wales Catchments Subgroup). The surface of the till is drumlinized in the Conwy Valley, on Mynydd Hiraethog and in the southern part of the Vale of Clwyd.
Thickness: Highly variable, locally in excess of 30m.
Geographical Limits: Mid and north-east Wales, and northern Welsh Borderlands.
Parent Unit: Plynlimon Glacigenic Formation (PLYNT)
Previous Name(s): Welsh Till (-3232)
Central Wales Drift (-4636)
Alternative Name(s): Meirion Formation
Stratotypes:
Partial Type Section  Stream section in tributary of the River Elwy, midway between Dhol and Tyn'n-y-coed; 1.8m of red clay of Irish Sea basin origin on yellow clay with abundant limestone , dolomite and Lower Palaeozoic pebbles and boulders (North Welsh origin - Merion Till) Warren et al. p.156 (1984); 1:10 000 GS Sheet SH97SE (1963) 
Reference(s):
Bowen, D Q, 1999. Wales. Chapter 7 in Bowen, D Q (Editor), A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No.23. 
Campbell, S and Bowen, D Q. 1989. Quaternary of Wales. Geological Conservation Review. (Peterborough: Nature Conservancy Council.) 
Davies, J R, Fletcher, C J N, Waters, R A, Wilson, D, Woodhall, D G and Zalasiewicz, J A, 1997. Geology of the country around Llanilar and Rhayader. Memoir for 1:50 000 Geological Sheets 178 and 179. 
Warren, P T, Price, D, Nutt, M J C and Smith, E G. 1984. Geology of the country around Rhyl and Denbigh. Memoir for 1:50 000 geological sheets 95 and 107 and parts of sheets 94 and 106. 
Thomas, G S P. 2005. North-east Wales. In Lewis, C A and Richards A E (eds). The glaciations of Wales and adjacent areas. Logaston Press. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable