. The Quarterly journal of the Geological Society of London. by Mr. Simpson & Mr. Glauert3 as an altered diabase,shows a much greater amount of brown hornblende, and in thisrespect constitutes a passage to the lustre-mottled brown hornblende is almost opaque from the presence ofinclusions of iron-ores, arranged for the most part in rows oblique i Bull. Geol. Surv. W. Austral. No. 8 (1903) p. 13.~ Ibid. No. 35 (1909) pp. 26, Ibid. pp. 27, 43. Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. to the vertical axis of the crystals (fig. 1). It is often crystallo-graphically co
. The Quarterly journal of the Geological Society of London. by Mr. Simpson & Mr. Glauert3 as an altered diabase,shows a much greater amount of brown hornblende, and in thisrespect constitutes a passage to the lustre-mottled brown hornblende is almost opaque from the presence ofinclusions of iron-ores, arranged for the most part in rows oblique i Bull. Geol. Surv. W. Austral. No. 8 (1903) p. 13.~ Ibid. No. 35 (1909) pp. 26, Ibid. pp. 27, 43. Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. to the vertical axis of the crystals (fig. 1). It is often crystallo-graphically continuous with clear green or colourless hornblende;but the boundary-line is sharp, with no shading of colours as in theKalgoorlie type. The bulk of the rock consists of clear, strongly-pleochroic, green hornblende in large and small crystals of more Fig. 1.—Hornblende-fels, 8140, Mavensthorpe, consisting oforiginal broivn hornblende (shaded, and with oblique roius of [lT~ iron-ores), secondary green hornblende (clear), and sphene(dotted). compact character than is the case with the simply-uralitizedamphibolites ; and it is evident that the rock has attained a higherdegree of metamorphism, most probably through analyses of pyroxenite-amphibolites from Western Australiaare available. (g) The Lustre-Mottled Amphibolites (Hornblende-Dolerite-Amphibolites). These rocks in Kalgoorlie do not form separate intrusions, butoccur as local variations of the main band of quartz-dolerite-amphibolite at two or three points on its western side. They mayeasily be detected in hand-specimens by the lustre-mottling on thecleavage-surfaces of large hornblende-crystals, which range up to15 mm. in their longest diameters. 640 DR. J. A. XHOMSON ON THE [Dec. I9I3, Owing to the large dimensions of the hornblende-crystals, only afew of these appear in a thin section of average size. They aremade up of variously coloured amphiboles, ranging from a deepbrown through a v
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
