^{page 366 note 1} The terms felsic and mafic have been proposed by Cross, Iddings, Pirsson, and Washington (Journ. Geol., xx, p. 560, 1912) as names for two main groups of rock-forming minerals, the one including quartz, felspars, and felspathoids; the other, pyroxenes, amphiboles, micas, olivine, iron-ores, etc. Variation in the relative proportions of these two groups constitutes the important mode of variation in igneous rocks which gives rise to leucocratic, mesocratic, and melanocratic types. A quantitative expression may be given to this variation by attaching the prefixes per- and do- to the terms felsic and mafic, with a similar connotation in respect to the mode as the analogous terms persalic, dosalic, etc., have in respect to the norm of the American Quantitative Classification.

^{page 367 note 1} Marshall, P., Q.J.G.S., lxii, p. 397, 1906.Google Scholar

^{page 367 note 2} Quensel, P., Bull. Geol. Inst. Upsala, xii, p. 130, 1914.Google Scholar

^{page 368 note 1} Pl. XI, Fig. 4.

^{page 370 note 1} Choffat, P., Mém. de la Soc. Phys. et d’Hist. Nat. de Genève, xxx, No. 2, 1888Google Scholar.

^{page 370 note 2} See also Kaiser, , in Bibliographie Géol. du Portugal et de ses colonies, ser. II, 1913, p. 21Google Scholar.

^{page 370 note 3} Passarge, , Adamaua, 1895, p. 384CrossRefGoogle Scholar.