Fig. 1: Sample of the Brodick breccia. This handsome, brick-coloured rock is composed of a medium- to fine-grained sandstone matrix enclosing rounded to tabular clasts. The colourful population of clasts, each 6 to 30 mm in maximum dimension, is dominated by white, milky quartz (vein quartz), and a pale green mica schist or phyllite.
Sample 218.01, 11x6.5x3 cm, 360 grams. Collected on 04 April 1974, from Brodick Beach just west of the pier, at NS022359, along the southern shore of Brodick Bay. This was my first field trip with new friends at Oxford, led by the incorrigible duo of Stewart McKerrow and Brian Atkins. This "rock" should be dedicated to them, and also to my father, whose 50th birthday this was!
"Rock of the Month # 255, posted for September 2022" ---
Arran is a substantial island, some 32 km N-S, and roughly 15 km wide along much of its length, rising to a maximum elevation of 874 masl (Ordnance Survey, 1960). Though much of the island, especially the higher ground, is composed of Tertiary igneous rocks associated with the opening of the North Atlantic Ocean, the long-standing attraction of the island for teaching introductory geology is the diversity of Phanerozoic rocks. Represented here are strata and igneous rocks of many ages: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian and Triassic strata, as well as (in the vicinity to the Paleogene magmatic rocks) evidence of strata of lower Jurassic and upper Cretaceous ages (Tyrell, 1928; McKerrow and Atkins, 1989).
The Brodick area displays Permian and Triassic strata of the New Red Sandstone, dominated by wind-blown, rounded aeolian sands (see Craig, 1965, pp.386-388, from which this paragraph is derived). The term New Red Sandstone refers to red bed sedimentary sequences found above the Carboniferous and below the Jurassic. These continental red beds are unfortunately for the most part unfossiliferous. Red sandstone of Permian age occupies much of the southern half of Arran. The Brodick breccia and local red Corrie sandstone occur on the basal sections of the New Red Sandstone in the area. At least part of the sequence may be upper Carboniferous, the rest Permian in age. Clasts include vein quartz, metamorphic rocks, Carboniferous sediments, volcanic rocks and agates. The agates may be derived from Carboniferous lavas. Cross-bedding can be seen in the Brodick breccia, and these sediments seem to be derived from the north or northwest.
The New Red Sandstone desert of the lower Permian is seen elsewhere in Europe, including Ireland (Sleeman et al., 2004). Permian and Mesozoic (Triassic, Jurassic and Cretaceous) strata in Ireland are mostly confined to the northeast, where they are preserved beneath the Tertiary lavas of the Antrim plateau (Wilson et al., 2001).
Craig,GY (1965) Permian and Triassic. In "The Geology of Scotland" (Craig,GY, editor), pp.383-400. Oliver & Boyd, Edinburgh and London / Archon Books, Hamden, CT, 556pp. plus map.
McKerrow,WS and Atkins,FB (1989) Isle of Arran: a field guide for students of geology. Geologists' Association Guide, 2nd edition, 104pp.
Ordnance Survey (1960) Isle of Arran. Ordnance Survey one-inch map 66, 1:63,360 scale, fully revised 1953-1954.
Sleeman,A, McConnell,B and Gately,S (2004) Understanding Earth Processes, Rocks and the Geological History of Ireland. Geological Survey of Ireland, 120pp. plus 1:1,000,000 scale map sheet and CD-ROM.
Tyrell,GW (1928) The Geology of Arran. British Geological Survey Memoir, HMSO, Edinburgh, viii+296pp., reprinted 1987.
Wilson,HE, Reid,REH, Parnell,J and Smith,RA (2001) Permian and Mesozoic. In "The Geology of Ireland" (Holland,CH, editor), Dunedin Academic Press, Edinburgh, 531pp., 331-351.
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