The BGS Lexicon of Named Rock Units — Result Details

Lees Hill Lava Member

Computer Code: LEHL Preferred Map Code: notEntered
Status Code: Full
Age range: Arundian Substage (CJ) — Asbian Substage (CR)
Lithological Description: The Lees Hill Lava Member consists predominantly of trachybasalt but also includes a plagioclase-macrophyric basalt lava (of 'Markle' type). The trachybasalt is typically fine grained, massive, locally slaggy and highly vesicular, and with local platy jointing. A single trachybasalt lava is present in the east [NS 7184 9247], which occurs as an intercalation within the macroporphyritic basalt lavas of the Gargunnock Hills Lava Member, near to its base. In the Gargunnock Burn ([NS 7065 9249] to [NS 7059 9222]) two trachybasalt lavas are present, separated by a plagioclase-macrophyric basalt lava which is absent farther west.
Definition of Lower Boundary: The basal trachybasalt of the member lies possibly disconformably on plagioclase-microphyric basalt (of 'Jedburgh' type) of the Spout of Ballochleam Lava Member. In the east of its outcrop, the member is represented by a single trachybasalt lava which overlies, apparently conformably or disconformably, a plagioclase-macrophyric basalt (of 'Markle' type) of the Gargunnock Hills Lava Member.
Definition of Upper Boundary: The Lees Hill Lava Member is overlain, apparently conformably or disconformably, by the Gargunnock Hills Lava Member, and in the east of its outcrop, the Lees Hills Lava Member is represented by a single trachybasalt lava, which is intercalated with lavas of the Gargunnock Hills Lava Member. The lithological change is to plagioclase-macrophyric basalt lava (of 'Markle' type).
Thickness: 0-37 m
Geographical Limits: The member is restricted to the northern Gargunnock Hills and northern Touch Hills, north-east of Glasgow. These rocks generally form the crest of the escarpment at the top of the cliffs formed by the Spout of Ballochleam Lava Member and crop out northwards from Gourlay's Burn ([NS 6628 8974] to [NS 6625 9003]) to Lees Hill [NS 660 910], east-north-east to Standmilane Craig [NS 6722 9180] and Black Craig [NS 6829 9219], and then eastwards through crags to the east of the Gargunnock Burn [NS 7195 9244].
Parent Unit: Clyde Plateau Volcanic Formation (CPV)
Previous Name(s): Lees Hill Group (-1022)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  In the northern Gargunnock Hills and northern Touch Hills, north-east of Glasgow Francis et al, 1970 
Reference(s):
Francis, E H, Forsyth, I H, Read, W A and Armstrong, M. 1970. The geology of the Stirling district. Memoir of the Geological Survey of Great Britain, Sheet 39 (Scotland). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S039