The BGS Lexicon of Named Rock Units — Result Details

Lewis Till Formation

Computer Code: LEWTI Preferred Map Code: LEW
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Compact greyish brown, matrix-supported diamicton with cobble to boulder sized subangular clasts mainly of Lewisian gneiss lithogies in a silty sand matrix. Generally becomes more gravelly towards the base, with angular clasts, and interstratified with sand in the uppermost metre or so, where boulders up to 2m in diameter are common. Forms gently undulating sheets.
Definition of Lower Boundary: Rests on broken or striated rock surface.
Definition of Upper Boundary: Generally capped by peat or alluvium deposits. Unconformably overlain by brown, matrix-supported, clast-rich diamicton of the Ruaival Diamicton Formation (Head) on St Kilda.
Thickness: Up to 6m
Geographical Limits: Outer Hebrides and St Kilda.
Parent Unit: Western Isles Glacigenic Subgroup (WISG)
Previous Name(s): Ruaival Drift (-1651)
Alternative Name(s): Dun Member
Stratotypes:
Type Section  Sea cliff section at the head of Holm Bay, Holm, 4km southeast of Stornoway, Isle of Lewis. Peacock, 1991 (illustrated in Plate 7). 
Reference(s):
Sutherland, D G. 1993. Outer Hebrides: Introduction, in Quaternary of Scotland. (Geological Conservation review series: 6) Gordon, J E and Sutherland, D G (editors). (London: Chapman and Hall). 413-414. 
Bowen, D Q. 1999. A revised correlation of Quaternary deposits in the British Isles. Geological Society Special Report, No. 23. 
Peacock, J D. 1991. Glacial deposits of the Hebridean region. 109-119 in Ehers, J, Gibbard, P L and Rose, J (editors), Glacial deposits in Great Britain and Ireland. (Rotterdam: Belkema.) 
Sutherland, D G, Ballantyne, C K and Walker, M J C. 1984. Late Quaternary glaciation and environmental change on St Kilda, Scotland, and their palaeoclimatic significance. Boreas, Vol.13, 261-272 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable