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II.—Traces of a Group of Permian Volcanos in the South-West of Scotland

Published online by Cambridge University Press:  01 May 2009

Archibald Geikie
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Extract

Although volcanic rocks of Permian age have long been known to occur abundantly in Germany, their existence in Britain does not appear to have been recognized up to the present time. Trapdykes, indeed, are far from rare among our Permian strata; there occur likewise many igneous masses penetrating the higher portions of the Carboniferous formation; but the former are evidently later than the Permian period, while the latter may be anterior to it. The history of volcanic action in the British isles, so far as I am aware, embraces as yet no clear evidence of Permian volcanos. In the present communication I propose to fill up this gap by showing that during the formation of the Permian sandstones a series of small but active volcanos was scattered over the south-west of Scotland.

Type
Original Articles
Information
Geological Magazine , Volume 3 , Issue 24 , June 1866 , pp. 243 - 248
Copyright
Copyright © Cambridge University Press 1866

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References

page 243 note 1 Murchison, , Siluria, p. 351Google Scholar, Quart. Geol. Soc. vii. 163; xii. 267Google Scholar. Binney, , Id., vol. xii. (1856) p. 138Google Scholar. Harkness, , Id., p. 262. It was not the objectof these observers to investigate the igneous rocks of the Ayr, and they treated them simply as intrusive masses, though the singular aspect of the “breccia” led Mr. Binney to remark that “the cementing paste has much the appearance of felspathic ash.”Google Scholar In a later paper (Quart. Journ. Geol. Soc. vol. xviii. (1862) p. 437) he expresses his doubt whether the trap seen near the breccia is interstratified or intrusive. In the course of an excursion into Ayrshire in 1862 I descended the course of the Ayr from Sorn to Stair and recognized the breccia as a true volcanic tuff; or gravelly ash, closely resembling the red trap-tuff of Dunbar. The trap at the same time was found to presentall the characters of true lava flows, and I saw it coming again to the surface on the westside of the basin. Though it was clear from these sections, that the Permian sandstones of Ayrshire contained at their base a contemporaneous volcanic series, I was unwilling to publish any paper on the subject until the whole of the ground had been examined. From the results of this excursion, however, the Permian basin was represented to be bounded by igneous rocks, on the east and west sides, on the Geological Map of the British Isles, published in 1864 in their Educational Series by Messrs. W. & A. K. Johnston, and in the Explanatory Handbook to that map (p. 67) I have referred to the true volcanic nature of the breccia and its associated trap. Since that time, the Geological Survey having been extended into Ayrshire, I have had an opportunity of mapping the Permian basin in detail. The full results will properly appear in the Official Memoirs, and I shall here, with the sanction of the Director General of the Survey, offer a brief summary of them.Google Scholar

page 248 note 1 [Trans. Roy. Soc., Edin., xx, p. 650.]Google Scholar