[46] Ibid., 229.
[47] Harker, "Slaty Cleavage and allied rock-structures," Rep. Brit. Assoc. (1885).
[48] Leith, "Rock Cleavage," Bull. U. S. Geol. Surv., No. 239 (1905).
[49] Lamplugh, "Geology of Isle of Man," Mem. Geol. Surv. Gt. Brit. (1903), 72-86.
[50] Darwin, "Geological Observations on S. America" (1846), chap. vi.
[51] Reade and Holland, "Green Slates of the Lake District, with a Theory of Slaty Cleavage," Proc. Liv. Geol. Soc. (1900-1), 124.
[52] A. Harker, "On 'eyes' of Pyrites &c.," Geol. Mag. (1889), 396.
[53] T. N. Dale illustrates an extreme case, "Slate Deposits of U.S.," Bull. U.S. Geol. Surv., No. 275 (1906), 31.