The BGS Lexicon of Named Rock Units — Result Details

Bell's Hill Volcanic Member

Computer Code: BHHB Preferred Map Code: BHHB
Status Code: Full
Age range: Pridoli Epoch (SO) — Lochkovian Age (DO)
Lithological Description: Pink, aphanitic, flow-banded rhyolite of flinty appearance with platy weathering. In thin section: cryptocrystalline, non-porphyritic, with no sign of fluxion or perlitic structures typical of higher rhyolites. The rhyolite is underlain locally by a thin conglomerate with subangular clasts of sandstone, chert and sporadic basic lava. Conglomerates are also intercalated with the rhyolite. At the top of the rhyolites sedimentary lenses are developed, consisting of bedded grey-green or purple micaceous sandstone with grains of quartz and microgranite, interbedded with conglomerates containing well-rounded greywacke, siltstone, microgranite and quartzite pebbles and angular rhyolite, microgranite, basalt and andesite pebbles derived from older lavas.
Definition of Lower Boundary: Unconformable: first appearance of pink flow-banded rhyolite unconformably overlying basalt and andesite flows of Bonaly Volcanic Member and thin conglomerates of the Greywacke Conglomerate Formation.
Definition of Upper Boundary: Conformable: pink flow-banded rhyolite overlain by fine-grained basalt of the Capelaw Volcanic Member in the north. Overlain in the south by micaceous sandstones and conglomerates of the Greywacke Conglomerate Formation, and by andesites and basalts of the Allermuir Volcanic Member.
Thickness: 315m maximum.
Geographical Limits: Pentland Hills.
Parent Unit: Pentland Hills Volcanic Formation (PDH)
Previous Name(s): Bell's Hill and Howden Burn Group [Obsolete Name and Code: Use BHHB, TDH] (-3849)
Bell's Hill and Howden Burn Volcanic Formation [Obsolete Name and Code: Use BHHB] (-1355)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Pentland Hills, 2 kms south of Swanston, Edinburgh. 
Type Section  White Cleugh and White Cleugh Burn. 
Reference(s):
Mykura, W, 1960. The Lower Old Red Sandstone igneous rocks of the Pentland Hills. Bulletin of the Geological Survey of Great Britain, No.16, 131-155. 
Mitchell, G H. 1962. The geology of the neighbourhood of Edinburgh. (Explanation of Sheet 32) Third Edition. (Reprinted 1980). Memoir of the Geological Survey of Great Britain (Scotland). 
Howell, H H and Geikie, A, 1861. The Geology of the neighbourhood of Edinburgh (1st edition). Memoir of the Geological Survey, Scotland. 
Mykura, W, 1986. Pentland Hills. 161-173 in Lothian Geology. An Excursion Guide. McAdam, A D and Clarkson, E N K (editors). (Edinburgh: Scottish Academic Press.) 
Cameron, I B and Stephenson, D, 1985. British Regional Geology: The Midland Valley of Scotland (3rd Edition). (London: HMSO for British Geological Survey). 
Geikie, A, 1897. The Ancient Volcanoes of Great Britain. Vol.1, 317-325. (London: Macmillan). 
Peach, B N, Clough, C T, Hinxman, L W, Grant Wilson, J S, Crampton, C B, Maufe, H B and Bailey, E B, 1910. The geology of the Neighbourhood of Edinburgh (2nd edition). Memoir of the Geological Survey of Scotland, Sheet 32 (Scotland). 
Thirlwall, M F, 1988. Geochronology of Late Caledenian magmatism in northern Britain. Journal of the Geological Society, Vol.145, 951-967. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S032 S032