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An Analcite-bearing Tuff in the Carboniferous Limestone of Derbyshire

Published online by Cambridge University Press:  01 May 2009

Extract

In the course of a recent study of the microscopic characters of the pyroclastic rocks of Derbyshire, a colourless, isotropic mineral, with refractive index considerably lower than that of the balsam, was noted in a thin section of a tuff from Cressbrook Dale. The rock consists essentially of a mass of lapilli containing much yellowish basaltic glass, often partially devitrified, and many felspar laths, sometimes with straight extinction, in a cement partly of calcite, and partly of amorphous, opaque material, white or grey by reflected light, which is probably decomposed volcanic detritus, of the same nature as the “toadstone-clays” of Derbyshire. Vitro-clastic structure is abundant.

Type
Original Articles
Copyright
Copyright © Cambridge University Press 1925

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References

page 462 note 1 At Owo the gneiss is riddled with coarse quartz veins.Google Scholar

page 462 note 2 For the latest description of this part of Nigeria and an admirable geological map, see Wilson, B. C., Bull. No. 2 Geol. Surv. of Nigeria, “The Geology of the Western Railway, Section I.”Google Scholar

page 463 note 1 Cf. Holmes, A., “Petrographic Methods and Calculations,” 1921, p. 279.Google Scholar

page 463 note 2 “General View of the Agriculture and Minerals of Derbyshire,” vol. i, 1815 (reprint), p. 443.Google Scholar

page 463 note 3 Sargent, H. C., “On a Spilitic Facies of Lower Carboniferous Lava-flows in Derbyshire,” Quart. Jour. Geol. Soc., vol. lxxiii, 1918, p. 21.Google Scholar

page 463 note 4 See Clarke, F. W., “The Data of Geochemistry,” Bull. U.S. Geol. Surv., No. 616, 3rd ed., 1916, pp. 369 and 416.Google Scholar