^{page 340 note 1} For a map showing the relation of this area to the Red Sea and to the Rift Valley of East Africa, see G. Dainelli & O. Marinelli in Atlante d'Africa, by Ghisleri, A., 1909, p. 139, fig. 6. The information from which the geological sketch-map was complied was mainly obtained from this publication (see pls. xxxi, xxxii, and pp. 133–9).Google Scholar

^{page 342 note 1} The springs are described in an Italian paper by M. Giua, of which an English summary is published in the Journ. Soc. Chem. Ind., vol. xxxvii, p. R 460, 1918.Google Scholar

^{page 343 note 1} African World, 08 18, 1917.Google Scholar

^{page 343 note 2} de Ropp, A., Journ. Ind. & Eng. Chem., vol. x, p. 839, 1918.CrossRefGoogle Scholar

^{page 344 note 1} Eng. & Min. Journ., vol. civ, p. 827, 1917.Google Scholar

^{page 344 note 2} Thun, E. E., Met. & Chem. Eng., vol. xvii, p. 693, 1917.Google Scholar

^{page 344 note 3} Eng. & Min. Journ., loc. cit.

^{page 345 note 1} SirHolland, T. H. & Fermor, L. L., Rec. Geol. Surv. India, vol. xlvi, pp. 210–15, 1915.Google Scholar

^{page 346 note 1} The ash or slaggy matter that remains when seaweed is burnt in a kiln for six or eight hours is called kelp; but in the United States the weed is kelp, and the product kelp-ash. The ash, as obtained on the west coast of Scotland, contains about 18 per cent of KCl and 13 per cent of K₂SO₄.

^{page 346 note 2} Since writing this paragraph I have been informed (April 24, 1919) by the Controller of Potash Production that most of the American kelp recovery plants have been shut down since the effective termination of the war. See also Journ. Soc. Chem. Ind. (June 15, 1919) for a recent statement of the potash position in the United States.

^{page 346 note 3} The World's Supply of Potash, Imperial Institute, 1915, p. 25.Google Scholar

^{page 347 note 1} Mem. Geol. Surv., Spec. Reps. on Mineral Resources, vol. v (Potash-Felspar, etc.), 1916Google Scholar; Boswell, P. G. H., Trans. Soc. Glass Technology, vol. ii, p. 35, 1918.Google Scholar

^{page 347 note 2} Wells, R. C., U.S.G.S., Prof. Pap. 98 D, p. 37, 1916.Google Scholar

^{page 347 note 3} Met. & Chem. Eng., vol. xviii, p. 65, 1918.Google Scholar

^{page 348 note 1} Rogers, A. H., Met. & Chem. Eng., vol. xv, p. 387, 1915.Google Scholar

^{page 348 note 2} Bradley, L., Journ. Ind. & Eng. Chem., vol. x, p. 804, 1918.Google Scholar

^{page 349 note 1} Ross, W. H., Journ. Ind. & Eng. Chem., vol. ix, p. 469, 1917.Google Scholar

^{page 349 note 2} Berry, R. A. & McArthur, D. N., Journ. Soc. Chem. Ind., vol. xxxvii, p. T 1, 1918.Google Scholar

^{page 349 note 3} Journ. Soc. Chem. Ind., vol. xxxvii, p. T 222, 1918.Google Scholar