The BGS Lexicon of Named Rock Units — Result Details

Port Beag Till Formation

Computer Code: PBTI Preferred Map Code: notEntered
Status Code: Full
Age range: Devensian Stage (QD) — Devensian Stage (QD)
Lithological Description: Reddish brown, matrix-supported diamicton with a notable proportion of clasts of Torridonian sandstone and, at the type section, blocks of the underlying organic sand and silt. Generally occurs as an interbedded and locally glacitectonically deformed sequence of shelly diamicton, silt, sand and gravel.
Definition of Lower Boundary: Irregular, unconformable contact with underlying deposits of organic sand and silt belonging to the Mid-Devensian Tolsta Head Member of the Lewis Formation of Bowen (1999).
Definition of Upper Boundary: Ground surface or unconformably overlain by glaciofluvial sand and gravel.
Thickness: Up to 25m
Geographical Limits: Northern Lewis, northeast of a prominent lateral moraine.
Parent Unit: Western Isles Glacigenic Subgroup (WISG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): Port Beag Member
Type Section  Cliff top section at Port Beag on the southern side of the Tolsta Head peninsula, Isle of Lewis. Gordon and Sutherland, 1993. 
Bowen, D Q. 1999. A revised correlation of Quaternary deposits in the British Isles. Geological Society Special Report, No. 23. 
Gordon, J E and Sutherland, D G. 1993. Tolsta Head, in Quaternary of Scotland (Geological conservation review series: 6) Gordon, J E and Sutherland, D G (editors). (London: Chapman and Hall). 423-425. 
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.) 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable