[Footnote 39: Lake and Rastall, "Text-book of Geology" (1910), 297. Compare C. Lapworth, "Intermediate Text-book of Geology" (1899), 176, and "Geological Structure of N. W. Highlands," Geol. Surv. Scotland (1907).] [Footnote 939: See A. B. Searle, "The Natural History of Clay" (1912).] [Footnote 40: Hall, "The Soil," ed. 2 (1908), 34, and E. J. Russell, "Clay," Standard Cyclopedia of Modern Agriculture (1908).] [Footnote 41: Reade and Holland, "Sands and Sediments," Proc. Liv. Geol. Soc. (1903-6).] [Footnote 42: Andrussow, "La Mer Noire," Guide des Excursions, vii^{me} Congrès géol. internat. (1897).] [Footnote 43: B. Smith, "Upper Keuper Sandstone," Geol. Mag. (1910), 302. Compare F. Cresswell, Trans. Leicester Lit. and Phil. Soc. (1910).] [Footnote 44: J. Murray and A. Renard, "Deep Sea Deposits," Challenger Rep. (1891), 231.] [Footnote 45: _Ibid._, 234.] [Footnote 46: _Ibid._, 229.] [Footnote 47: Harker, "Slaty Cleavage and allied rock-structures," Rep. Brit. Assoc. (1885).] [Footnote 48: Leith, "Rock Cleavage," Bull. U. S. Geol. Surv., No. 239 (1905).] [Footnote 49: Lamplugh, "Geology of Isle of Man," Mem. Geol. Surv. Gt. Brit. (1903), 72-86.] [Footnote 50: Darwin, "Geological Observations on S. America" (1846), chap. vi.] [Footnote 51: Reade and Holland, "Green Slates of the Lake District, with a Theory of Slaty Cleavage," Proc. Liv. Geol. Soc. (1900-1), 124.] [Footnote 52: A. Harker, "On 'eyes' of Pyrites &c.," Geol. Mag. (1889), 396.] [Footnote 53: T. N. Dale illustrates an extreme case, "Slate Deposits of U.S.," Bull. U.S. Geol. Surv., No. 275 (1906), 31.] [Footnote 54: Harker, _op. cit._, ref. 47, p. 19.] [Footnote 55: Leith, _op. cit._, ref. 48, p. 152.] [Footnote 56: I. Russell, "Glaciers of N. America" (1897), 25.] [Footnote 57: See, for instance, T. W. Edgeworth David, "Evidences of glacial action in Australia," Q. Journ. Geol. Soc., =52= (1896), 289.] [Footnote 58: For general discussions of Igneous Rocks, see J. J. H. Teall, "British Petrography" (1888); H. Rosenbusch, "Mikroskopische Physiographie," ed. 4 (1905-7); F. Zirkel, "Lehrbuch der Petrographie," ed. 2 (1894); A. Harker, "Natural History of Igneous Rocks" (1909); J. P. Iddings, "Igneous Rocks," 1 (1909).] [Footnote 59: Cross, Iddings, Pirsson, and Washington, "Quantitative Classification of Igneous Rocks" (1903).] [Footnote 60: Harker, _op. cit._, ref. 58, p. 186.] [Footnote 61: Iddings, _op. cit._, ref. 58, p. 130 &c.] [Footnote 62: _Ibid._, pp. 228-241.] [Footnote 63: Scrope, "Considerations on Volcanos" (1825), 141.] [Footnote 64: G. A. J. Cole and J. W. Gregory, "Variolitic Rocks of Mt Genèvre," Q. Journ. Geol. Soc., =46= (1890), 311.]