VI. Preliminary Notes on Volcanic Necks in North-west Ayrshire

Abstract

THE area under consideration lies in the adjoining margins of the Geological Survey maps, sheets 21 and 22, Scotland, on •which a large number of volcanic necks are shown to occur.Sir Archibald Geikie (1897, pp. 394 seq.; 1903, pp. 65-6), who has given several short accounts of them, considers that they are the sites of some of the volcanoes which gave rise to the Calciferous Sandstone lavas. During the recent revision of this area by the Geological Survey several new volcanic necks have been recognised, and fresh evidence has been gathered about some of the others. In the map of the district (Fig. 1) the various necks are each given a separate number, and for facility of reference the same numbers will be used in the following account. DESCRIPTION OF THE NECKS. Vents Containing Acid Materials.-TheIrish Law vent (No. 1) forms the south extremity of the great volcanic centre of Misty Law, and most probably represents a late phase of activity. Its margins are only seen on the west in the sections on the sides of Rye Water Head, where a coarse-grained pink and green volcanic breccia is in contact with a pink felsitic rock. Further north the margin can be seen cutting across the Gogo Water. To the south it has been traced in a south easterly direction to the west slopes of Knockside Hills (Figs. 2 and 3). The eastern margin is covered by peat, but is taken as running in a north-easterly direction. Several masses of trachytic and basaltic rocks occur in the vent, interesting occurrences being on Irish Law. The breccia in the vent con tains numerous trachytic fragments and therefore it looks as if the junction between the two rocks was of an explosive nature, with shattering of the already consolidated trachyte.

XIII.— The Old Red Sandstone Rocks of the West Kilbride-Largs District, Ayrshire

“…Some of these have been described by A. Geikie (1903, pp. 65-66) and in later years by G. V. Wilson (1916). The present writer has noted two necks not so far recorded, one forming the northern end of Campbeltown Hill, just west of Campbeltown Farm, the other occurring between tide-marks on the shore of Ardneil Bay (Fig.…”

Early Carboniferous minor intrusions of the Clyde Plateau: new data from the Cumbrae islands

“…1;Smedley 1986a, p. 266, 317;Fig. 3), the high proportion of augite and olivine suggesting a transitional rock type between 'Dunsapie' basalt and 'Craiglockhart' ankaramite. The presence of megacrysts of black augite (some >10 cm long) recalls the similar rock forming the Black Rock vent at the south end of Fence Bay, Fairlie, on the North Ayrshire mainland (Young 1894;Smellie 1916;Wilson 1916;Tyrrell 1918;Patterson 1949;Alexander et al 1986;Stephenson 1999). Flanked by slivers of agglomerate containing xenolithic fragments of Kelly Burn Sandstone, Bell Craig is the one intrusion on the island that can be interpreted unequivocally as a volcanic neck.…”

“…This is built around the large vent at Hill of Stake, where a patch of the youngest feldspar macrophyric basaltic rocks within the centre is surrounded by a broad zone of trachytic lavas and associated trachytic agglomerates and tuffs. The Misty Law Trachytic Centre as a whole refers to the 300 mthick shallow-conical mass of felsic lavas and tephra marking the site of the central-type, volcano of that name -at 6•5 km by 4•0 km the largest of the Clyde Lava Plateau -in the central Renfrewshire Hills, some 6 km ENE of Largs (Geikie 1897;Wilson 1916;Johnstone 1965;Stephenson in Paterson et al 1990;British Geological Survey 1990; Figs 1, 3, 11).…”

The Early Carboniferous volcanic outliers of Little Cumbrae and south Bute: implications for westward attenuation of the Clyde Lava Plateau

“…Volcanism seems to have been entirely subaerial, but beyond that, the locus and mode of eruption remain unclear. Central-type vents have not been found on Little Cumbrae, but are scattered through south Bute, Great Cumbrae and the adjoining coastal mainland from Seamill and West Kilbride north to Fairlie and Largs (Geikie 1897;Gunn 1903;Wilson 1916;Smellie 1916;Tyrrell 1918;Patterson 1952;Stephenson 1999;British Geological Survey 2005). Many of these are tiny and would qualify as 'puys' in Geikie's (1897) original classification, to be distinguished from the considerably larger, agglomerate-filled vents that penetrate both the sedimentary and volcanic rocks of the mainland and from the huge, composite 'plateau vent' of Misty Law (Geikie 1897;Johnstone 1965), which was the site of central-type, multi-vent eruptions of more silicic lavas and pyroclastic rocks during generation of the Renfrewshire tablelands.…”

“…South Bute has fared somewhat better. In contrast, the igneous rocks of the Renfrewshire-Kilbirnie hills have been studied more fully and more recently (Geikie 1897(Geikie , 1903Wilson 1916;Richey 1928;Richey et al 1930;Johnstone 1965;Paterson et al 1990;Stephenson 1999;British Geological Survey 2005). Bearing most directly on the present study has been Smedley's (1986aSmedley's ( , b, 1988a) determination of the chemical composition of some seventy different lavas from Little Cumbrae, South Bute and the Renfrewshire-Kilbirnie hills, which provided information useful in correlation.…”