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VI.—The Petrology of Arran

Published online by Cambridge University Press:  01 May 2009

G. W. Tyrrell
G. W. Tyrrell
Affiliation:
Assistant to the Professor of Geology, University of Glasgow.
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Extract

The Riebeckite-Orthophyre of the Holy Isle.—Four Occuxrences of acid and sub-acid igneous rocks containing the rare soda-amphibole riebeckite have been recognized in Great Britain, of which that of Ailsa Craig is the best known. The occurrences of Ailsa Craig and Mynydd Mawr, Carnarvonshire, are riebeckite-microgranites or paisanites. They contain ragged moss-like areas of riebeckite, together with microphenocrysts of quartz and alkalifelspar, in a microcrystalline groundmass of quartz and felspar. Riebeckite was also found by Dr. Teall in the granophyre of Meall Dearg and the neighbouring area of Druim an Eidhne, Skye. Harker described the riebeckite in these rocks as occurring in two forms, one having the usual ragged, sponge-like appearance, and the other being idiomorphic, the faces in the prism zone being well-defined, but with irregular terminations. The fourth occurrence differs somewhat from the others. This rock occurs as an intrusion into the Upper Old Red Sandstone, or Calciferous Sandstone of Easter Eildon Hill, Melrose, and was described by Barron as riebeckite-trachyte or phonolite. It consists principally of sanidine, occurring both as microphenocrysts and in the groundmass, with interstitial patches of riebeckite, and a little nepheline. Harker describes the rock as an orthophyre.

Type
Original Articles
Information
Geological Magazine , Volume 10 , Issue 7 , July 1913 , pp. 305 - 309
Copyright
Copyright © Cambridge University Press 1913

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References

page 305 note 1 Teall, Min. Mag., ix, 219–21, 1891.Google Scholar

page 305 note 2 Harker, , Bala Vole. Ser. Carnarvon, 1889, pp. 50–2.Google Scholar

page 305 note 3 Q.J.G.S., 1, 219, 1894.Google Scholar

page 305 note 4 Tertiary Igneous Bocks of Skye (Mem. Geol. Surv.), 1904, p. 158.Google Scholar

page 305 note 5 Geol. MAG., 1896, p. 376.Google Scholar

page 305 note 6 Petrology for Students, 4th ed., 1908, p. 129Google Scholar; see fig. 33B, p. 128.

page 305 note 7 The Geology of North Arran, South Bute, and the Cumbraes (Mem. Geol. Surv.), 1903, p. 70.Google Scholar

page 306 note 1 Geology of North Arran, etc., p. 91.Google Scholar

page 307 note 1 Summ. Prog. Oeol. Surv. for 1909, 1910, p. 52.Google Scholar

page 307 note 2 The Geology of Knapdale, Jura, and North Kintyre, 1911, pp. 116–18Google Scholar; The Geology of Colonsay and Oronsay, with Part of the Ross of Mull (Mem. Geol. Surv.), 1911, pp. 41–6.Google Scholar

page 307 note 3 The Geology of Colonsay and Oronsay, 1911, p. 41.Google Scholar

page 307 note 4 The Geology of Knapdale, Jura, and North Kintyre, 1911, p. 117.Google Scholar

page 307 note 5 For analyses of teschenites see The Geology of the Neighbourhood of Edinburgh (Mem. Geol. Surv.), 1910, p. 299.Google Scholar

page 308 note 1 Tscherm. Min. Petr. Mitth., xiv, 463–5, 1895.Google Scholar

page 308 note 2 The Geology of North Arran, South Bute, and the Cumbraes (Mem. Geol. Surv.), 1903, pp. 112–14.Google Scholar

page 309 note 1 Q.J.G.S. xxx, 563, 1874Google Scholar.

page 309 note 2 Tyrrell, , Geol. Mag. (V), IX, 124, 1912Google Scholar.