SINCE this paper was printed, a memoir by Prof. Sauer, on the peculiar blue hornblende from Socotra, has appeared (Zeitsch. d. Deutsch : geol. Gesellsch. Vol. XL. p. 138). It is found on analysis to have more SiO₂), much more Fe₂O₃, and less FeO than Arfvedsonite, so that he proposes the separate name Riebeckite.