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VII.—The Late Palæozoic Alkaline Igneous Rocks of the West of Scotland

Published online by Cambridge University Press:  01 May 2009

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

2. Essexite. (a) Carskeoch type.—A small boss of essexite, of rather basic type, pierces the agglomerate of the Carskeoch vent, near Patna, Ayrshire. Macroscopically it is light grey, compact, and fine-grained. In thin section it shows a plexus of fluxionally-arranged plagioclase laths of the composition Ab An, the interstices being filled with subhedral augite of a nearly colourless variety, and fresh olivine. Here and there minute angular interspaces are occupied with turbid isotropic matter, the form and arrangement of the particles of which suggest the former presence of nepheline. A few broad plates of pale augite and crystals of olivine interrupt the general trachytoid fabric. Ilmenite and biotite occur sparsely, and a little orthoclase may be detected on the margins of the plagioclases, extending irregularly into the interspaces. This rock has a distinct individuality, and resembles neither the essexites of Lochend and Craigleith in the Lothians, nor the Crawfordjohn type described below. It is poor in alkali-felspars and felspathoids, is devoid of purple augite, and has a well-developed trachytoid fabric.

Type
Original Articles
Information
Geological Magazine , Volume 9 , Issue 3 , March 1912 , pp. 120 - 131
Copyright
Copyright © Cambridge University Press 1912

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References

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page 121 note 2 Bailey, loc. Cit.

page 123 note 1 This includes a little unidentified turbid matter.

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page 126 note 2 Ibid., pp. 106–7.

page 126 note 3 Ibid., p. 109.

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