^{page 168 note 1} See for example: Keilhack, K., Lehrbuch der praktischen Geologie, 3rd ed. vol. ii, 1917Google Scholar; Ries, H., Clays, their Occurrence, Properties, and Uses, 2nd ed., p. 141, 1914Google Scholar; Crook, T., Appendix to Hatch and Rastall, The Sedimentary Socks, p. 343, 1913Google Scholar; Baker, H. A., “Mechanical Constitution of Loose Arenaceous Sediments”: Geol. Mag., Vol. LVII, 1920, p. 323Google Scholar; Harder, P., “Undersögelser over nogle dansko Sandsorters Avendelighed til Formsand i Jernstöberier”: Dan. Geol. Undersög., ser. ii, No. 16, 1905.Google Scholar

^{page 169 note 1} Cf. Strahan, , “The Geology of the Neighbourhoods of Flint, Mold, and Kuthin”: Mem. Geol. Surv., 1890, p. 47 et seq.Google Scholar

^{page 169 note 2} Cf. Smith, B., “Special Reports on the Mineral Resources of Great Britain” vol. xixGoogle Scholar, “Lead and Zinc Ores in the Carb. Rocks of N. Wales”: Mem. Geol. Surv., 1921, pp. 36 and 38.Google Scholar

^{page 169 note 3} Wheelton, Hind and Stobbs, J. T., “The Carboniferous Succession below the Coal-Measures in North Shropshire, Denbighshire, and Flintshire”: Geol. Mag., 1906, p. 502.Google Scholar

^{page 170 note 1} Op. cit., p. 504.

^{page 170 note 2} Cf. Hind, W. and Howe, J. A., “The Geological Succession and Palæontology of the Beds between the Millstone Grit and the Limestone Massif of Pendle Hill, and their equivalents in certain other parts of Britain”: Q.J.G.S., vol. li, p. 376.Google Scholar

^{page 170 note 3} Op. cit., p. 505.

^{page 170 note 4} Strahan, op. cit., p. 47.

^{page 170 note 5} Strahan, op. cit., p. 51, and B. Smith, op. cit., p. 129.

^{page 172 note 1} Op. cit., p. 505.

^{page 172 note 2} Op. cit., p. 53.

^{page 172 note 3} Cf. B. Smith, op. cit., p. 38.

^{page 172 note 4} Cf. Strahan, op. cit., p. 13.

^{page 172 note 5} Morton, G. H., “The Carboniferous Limestone and Cefn-y-fedw Sandstone of Flintshire”: Proc. Liverpool Geol. Soc., vol. iv, 1885, p. 402.Google Scholar

^{page 172 note 6} Op. cit., p. 49.

^{page 173 note 1} Strahan, op. cit, p. 26.

^{page 173 note 2} Op. cit., p. 50.

^{page 173 note 3} Op. cit., pp. 48 et seq.

^{page 177 note 1} Op. cit., p. 500.

^{page 178 note 1} Op. cit., p. 396, and pl. xxii.

^{page 178 note 2} Op. cit., p. 400.

^{page 178 note 3} Op. cit., pp. 41–4.

^{page 178 note 4} Cf. Sargent, H. C., “The Lower Carboniferous Chert Formations of Derbyshire”: Geol. Mag., Vol. LVIII, 1921, p. 274.Google Scholar

^{page 179 note 1} H. C. Sargent, op. cit., which see for a fuller discussion of the problems considered in this and the following sections.

^{page 179 note 2} Op. cit., p. 47.

^{page 180 note 1} H. C. Sargent, op. cit., p. 267.

^{page 180 note 2} Cf. Greenly, E., “The Geology of Anglesey”: Mem. Geol. Surv., 1919, p. 604.Google Scholar

^{page 180 note 3} Ibid., p. 715.

^{page 180 note 4} “On Silica and the Siliceous Remains of Organisms in Modern Seas”: Proc. Roy. Soc. Edin., vol. xviii, 1891, pp. 229–50.Google Scholar

^{page 180 note 5} Cf. Tarr, W. A., “Origin of the Chert in the Burlington Limestone”: Amer. Journ. Set., vol. xliv, 1917, p. 436. Also R. S. Dean, Amer. Journ. Set., vol. xlv, 1918, p. 413.Google Scholar

^{page 180 note 6} Op. cit., p. 237.

^{page 181 note 1} Davis, E. F., “The Radiolarian Cherts of the Franciscan Group”: Univ. Cal. Pub. Geol, vol. xi, 1918, p. 382.Google Scholar

^{page 181 note 2} Ibid., p. 383.

^{page 181 note 3} Davis, op. cit., pp. 399–400.

^{page 181 note 4} “The Coral Reefs and other Carbonate of Lime Formations in Modern, Seas”: Proc. Roy. Soc. Edin., vol. xvii, 1889, p. 92.Google Scholar

^{page 181 note 5} Op. cit., p. 13.

^{page 182 note 1} Cf. Boswell, P. G. H., “Sedimentation, Environment, and Evolution in Past Ages”: Pres. Add., Trans. Liverpool Biol. Soc., vol. xxxv, 1921, p. 9.Google Scholar