The BGS Lexicon of Named Rock Units — Result Details

Glas Eilean Lava Formation

Computer Code: GEIL Preferred Map Code: GEIL
Status Code: Full
Age range: Cisuralian Epoch (PLC) — Cisuralian Epoch (PLC)
Lithological Description: Alkali olivine-basalt intercalated with sedimentary rocks. A basal reddish-brown conglomeratic sandstone, with clasts up to about cobble size, and red to reddish-brown fine-grained sandstone is overlain by a sequence of basalt lavas [Pringle and Bailey, 1944]. Each lave flow is less than 2m thick [Upton et al., 1987] and amygdaloidal; some flows have slaggy tops. Reddish sandstone is present as isolated lenses. Sandstone, calcareous sandstone and sandy limestone may overlie and infill fissures within the lavas [Pringle and Bailey, 1944]. The thicker lava flows occur towards the base of the succession, average flow thickness decreases upwards with increasing amount of sedimentary intercalations. The basalts are sparsely microphyric with phenocrysts mostly of olivine, plagioclase and augite [Upton et al., 1987].
Definition of Lower Boundary: Conglomeratic sandstone at the base of the Formation, approximately 7m thick [Pringle and Bailey, 1944], is inferred to overlie Dalradian rocks unconformably [Upton et al., 1987].
Definition of Upper Boundary: Overlying rocks no longer preserved.
Thickness: >120m
Geographical Limits: Onshore exposures on the islet of Glas Eilean and the Black Rock Skerries, and underlying the Sound of Islay between the islands of Islay and Jura, Argyll, Scotland.
Parent Unit: Stewartry Group (STEW)
Previous Name(s): Lower Old Red Sandstone Lavas (-3425)
Carboniferous Lavas (-279)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Coastal exposures on the islet of Glas Eilean in the Sound of Islay, Argyll, Scotland. Pringle and Bailey, 1944. 
Reference(s):
Geike, A. 1899. Summary of Progress for 1898. Memoir of the Geological Survey, p75. 
Jin, Y, Wardlaw, B R, Glenister, B F and Kotlyar, G V. 1997. Permian chronostratigraphic subdivisions. Episodes, Vol.20, 10-15. 
Upton, B G J, Fitton, G J and Macintyre, R M. 1987. The Glas Eilean lavas: evidence of a Lower Permian volcanotectonic basin between Islay and Jura, Inner Hebrides. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol.77, 289-293. 
Pringle, J and Bailey, E B. 1944. The Carboniferous rocks of Glas Eilean, Sound of Islay, Argyllshire. Transactions of the Geological Society of Glasgow, Vol.20, 249-259. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S028 S027