OF MOUNT EREBUS, ANTARCTICA 121 



Igneous Inclusions in Beacon Sandstone. Mr. Priestley left in my hands for 

 examination two microsections of Beacon sandstone with somewhat decomposed 

 inclusions of igneous rock. At first it was thought that the included lava fragments 

 were kenyte, to some of which they bore strong resemblance in texture. The minerals 

 were somewhat decomposed, so that identification was rendered difficult. A closer 

 examination of the slides revealed that the fragments bore a more strongly marked 

 resemblance to the kersantites described by Prior, and figured fig. 4, Plate IX, of his 

 report. These rocks, being intrusive into the basement rocks of Victoria Land, would 

 be more likely to occur in sandstone than would kenyte. 



The trachyte with pseudomorphs after hornblende from Cape Bird is much more 

 basic than the normal trachytes tabulated in Table I (p. 98), and even more basic than the 

 kenytes. Yet it is a typically trachytic rock in hand-specimen and under the micro- 

 scope but for the abundant pseudohornblendes. It is these inclusions which account for 

 the basicity of the rock, raising the percentages of ferrous iron, magnesia, alumina, 

 and lime at the expense of silica. Comparison with analyses C and D, which with E 

 are quoted from Washington's Analyses of Igneous Rocks shows that this trachyte 

 is not a kulaite, for magnesia and lime are not as high and the alkalies higher than 

 should be the case in this group. 



The kulaitic basalt (numbered 648) also varies in composition from typical kulaite 

 and is almost identical in composition with a basalt (Analysis, Table IT, E, p. 120) from 

 the Siebengebirge. which is also a noted alkaline province. The close chemical relation- 

 ship of the basic kenytes to the kulaitic basalts has already been referred to (cf. 

 Table II, p. 110), as has also the similarity in composition of this rock to the basic 

 autogenic inclusions in tephritic trachyte from Columbretes. 



Calculated in the American classification the kulaitic basalt is in the subrang 

 Hessose, where its true affinities are quite obscured, and the trachyte J. 18 falls in the 

 subrang Essexose, which is also an unnatural group for a rock of its mineralogical 

 features to fall into. (See Table VI. p. 123.) 



THE KULAITE SERIES 



J. 36 (1944). Kulaite, Mount Bird. — The hand-specimen is a rough-fractured, grey, 

 andesitic-looking rock, megaphyric in larger felspars and smaller pyroxenes. 



The texture is porphyritic hiatal, dopatic, magnophyric with a hypocrystalline 

 hyalopilitic fabric inclined to the diabasic structure. 



The phanerocrystalline constituents consist of labradorite felspar, large phenocrysts 

 of bistre augite, smaller crystals of light-brownish augite, and occasional grains of 

 corroded olivine. There are also numerous dark patches whose outlines suggest that 

 they are pseudomorphs after hornblende. These are resolved by the high power into 

 a mixture of magnetite, colourless diopside, hypersthene needles, and felspar as described 

 by Washington.* (See Plate III, fig. 6.) 



The ground-mass consists of acicular labradorite crystals, augite, enstatite, and 

 magnetite. The augite belongs to the same species as that of the phenocrysts. Many 

 of the finer constituents are simply fragmentary portions of broken- up pyroxene, 

 felspar phenocrysts, and of the pseudomorphs, and belong, strictly speaking, to the 

 first generation. 



The second-generation minerals are, with the exception of the pseudohornblende, 

 identical with those of the first generation. In addition, rod-shaped enstatites are 

 present. 



An isotropic glass, probably of leucitic composition, occurs interstitially. 



* Jour. ofGeol., April-May 1896. 



