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^{page 266 note 2} Most of these details of thickness are taken from “The Geology of the Northern Part of the Derbyshire Coalfield”: Mem. Geol. Surv., 1913, p. 20.Google Scholar

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^{page 267 note 1} Garnett, C. S. has shown that the colour of “Blue John” is due to bituminous matter (Trans. Chem. Soc, vol. cxvii, 1920, pp. 621–3).Google Scholar

^{page 268 note 1} Cf. Tarr, W. A., “Origin of the Chert in the Burlington Limestone”: Amer. Journ. Sci., vol. xliv, 1917, p. 422.Google Scholar

^{page 269 note 1} “Processes of Mineralization and Enrichment in the Tintic Mining District”: Econ. Geol., vol. x, 1915, p. 233.Google Scholar

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^{page 270 note 1} “Organic Origin of Chert”: Geol. Mag., 1887, p. 445.Google Scholar

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^{page 271 note 3} Cf. Davis, E. F., “The Radiolarian Cherts of the Franciscan Group”: Univ. Cal. Pub. Bull. Dep. Geol., vol. xi, 1918, p. 366.Google Scholar

^{page 271 note 4} Cf. Hinde, G. J., “On Beds of Sponge Remains in the Lower and Upper Greensand of the South of England”: Phil. Trans., pt. ii, 1885, p. 431.Google Scholar

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^{page 272 note 1} Op. cit., p. 370.Google Scholar

^{page 272 note 2} The Data of Geochemistry, 1916, p. 130.Google Scholar

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^{page 272 note 6} “The Origin of Chert”: Amer. Journ. Sci., vol. xlv, 1918, p. 456.Google Scholar

^{page 272 note 7} “The Chert of the Wreford and Foraker Limestones along the State Line of Kansas and Oklahoma”: Amer. Journ. Sci., vol. xlvii, 1919, pp. 407–29.Google Scholar

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^{page 272 note 9} Op. cit., p. 429.Google Scholar

^{page 272 note 10} Op. cit., p. 417.Google Scholar

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^{page 273 note 1} Cf. Dean, , “The Formation of Missouri Chert”: Amer. Jonrn. Sci., vol. xlv, 1918, p. 413. Also Tarr, op. cit,, pp. 434–6.Google Scholar

^{page 273 note 2} Op. cit., p. 324.Google Scholar

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^{page 274 note 1} Op. cit., p. 427.Google Scholar

^{page 275 note 1} Op. cit., pp. 399–401.Google Scholar

^{page 276 note 1} Sargent, H. C., “On a Spilitic Facies of Lower Carboniferous Lava Flows in Derbyshire”: Quart. Journ. Geol. Soc., vol. lxxiii, 1918, pp. 11–23.Google Scholar

^{page 276 note 2} Mineral Deposits, 1913, p. 52.Google Scholar

^{page 276 note 3} Cf. Dewey, and Flett, , “On some British Pillow-lavas and the Rocks associated with them”: Geol. Mag., 1911, p. 245. Also Flett, “The Iron-ore Deposits of Nobblehouse and Garron Point and their Genesis” (Edin. Geol. Soc.) Abstract in Geol. Mag., Vol. LVI, 1919, p. 92.Google Scholar

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^{page 277 note 1} Hinde, G.J., “Organic Origin of Chert”: Geol. Mag., 1887, p. 445.Google Scholar

^{page 277 note 2} Geol Mag., 03, 1921, pp. 114–24.Google Scholar

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^{page 278 note 1} “The Nature of Replacement”: Econ. Geol., vol. vii, 1912, p. 529.Google Scholar

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