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Published online by Cambridge University Press: 14 March 2018
In the south-west coal-field of east Glamorganshire—especially in the Lower Coal Measures–Mr. A. Tait, of Caerphilly, observed last year a white, soft, and pulverulent substance, saponaceous to the touch. A specimen sent to me, examined first and identified by Mr. T. Crook, was found to consist of a congeries of well-defined crystals of kaolinite. The crystals are chiefly basal flakes, hexagonal in outline, and 0.02 to 0.037 mm. in length. Most of them show elongation in one direction, and unequal extension of the thin lamellae composing them.
Page 64 note 1 See Lacroix, A., ‘Minéralogie de la France,’ 1895, vol. i, pp. 467–470 Google Scholar.
Page 64 note 2 Lang, R., Centralblatt Min. Geol., 1909, pp. 596–599 Google Scholar.
Page 65 note 1 Gagel, C., Centralblatt Min. Geol., 1909, pp. 437 and 467-475Google Scholar.
Page 65 note 2 Stremme, H., Zeits. prakt. Geol., 1908, vol. xvi, pp. 125–128 Google Scholar.
Page 65 note 3 F. Weiss, ibid., 19109 vol. xviii, pp. 358-367.
Page 65 note 4 F. Wüst, ibid., 1907, vol. xv, p. 19.
Page 65 note 5 Röslerl, H., Zeits. prakt. Geol., 1908, vol. xvi, p. 251 Google Scholar, questioning the correctness of Stremme's description of a bed of altered rock as kaoliniferous, observes that it contains what appears to be a scaly sericitic mineral. That this has resulted from chemical change in kaolinite seems quite possible.
Page 66 note 1 J. Morozewicz, Kosmos, Lemborg, 1907, vol. xxxii, p. 496 ; for abstract, see Zeits. Kryst. Min., 1910, vol. xlviii, p. 523.
Page 66 note 2 On the constitution of the micas, see Clarke, F. W., Bull. United States Geol. Survey, 1895, No. 125, p. 45.Google Scholar.
Page 67 note 1 For other examples of fluorization see Butler, F. H., Mineralogical Magazine. 1908, vol. xv, pp. 139–141 Google Scholar.
Page 67 note 2 Bischof, G., ‘Chemische Untersuchung der Mineralwasser zu Geilnau, &c.,’ Bonn, 1826, pp. 302–809 Google Scholar. See also Flett, J. S., Mem. Geol. Survey, ‘Geol. of Bodmin and St. Austell,’ 1909, p. 118 Google Scholar, par. 2.
Page 67 note 3 Teall, J. J. H., ‘British Petrography,’ 1888, p. 314 Google Scholar.
Page 68 note 1 See Mem. Geol. Survey, ‘Geology of Bodmin and St. Austell,’ 1909, p. 108. The map of the St. Austell granite there given shows strikingly irregular extension of the kaolinized areas alongside the included tin-lodes—a feature favouring the view that kaolinization took place quite independently of and previous to the formation of the lode-fissures.
Page 68 note 2 McLintock, W. F. P., Mineralogical Magazine, 1910, vol. xv, pp. 407–408 CrossRefGoogle Scholar.
Page 68 note 3 The presence in china-clay of small quantities of bases not contained in kaolinite has been repeatedly demonstrated. Four samples of Cornish chinaclay of the best qualitY analysed by W. Jackson and A. G. Richardson (Trans. English Ceramic Soc. Tunstall, Staff., 1905, vol. iii (]903-4), p. 56) gave an proaverage composition of alkalis 2.785, CaO 0.13, MgO 0.12, Fe20 s 0.625 with SiO2 46.127, Al2O3 38.091 and water 12.157, in a total of 100.034. The proportions of the different mineral constituents were : clay-substance 97.372, quartz 0.897 s 1.6851 in a total of 99.95. Still larger amounts of bases other than alumina were obtained in, some of W. I. Macadam's analyses : see Mineralogical Magazine, 1880, vol. vii, p. 76.
Page 69 note 1 Hickling, Cf. G., Trans. Manchester Geol. and Mining Soc., 1908, vol. xxx, p. 355 Google Scholar ; and Mere. Geol. Survey, ‘Geology of Land's End,’ 1907, p. 58, par. 3.
Page 69 note 2 Lasius, G. S. O., ‘Beobachtungen über das Harzgebirge,’ 1789, Theil i, pp. 77–80 Google Scholar.
