OF MOUNT EREBUS, ANTARCTICA 107 



material contains minute magnetite needles (incipient skeleton crystals), and brownish 

 belonites of titaniferous augite just commencing to devitrify out of the glass. 

 Pyroxene belonites and glassy felspathoids were clearly the last products of 

 consolidation. 



The leucites possess the characteristics of the leucite from the Cape Royds kenyte 

 described by Dr. G. T. Prior*; they are often feebly birefringent because of 

 alteration to pseudoleucite. The felspar microlites consists of anorthoclase. 



Prior gives an analysis and photo of a similar specimen. For Analysis see A, 

 Table II, p. 110, or Analysis No. 3, p. 119, vol. i, National Antarctic Expedition of 

 1901-1904. For illustration see Plate III, fig. 1, and Plate VIII, fig. 3, National 

 Antarctic Expedition, 1901-1904, vol. i. 



J. 64 (1963), P. 54. Half-way between Cape Royds and Cape Barne, one mile south 

 of Back-Door Bay. — This rock is similar to the Erebus specimen, but contains some 

 titaniferous pyroxene phenocrysts. 



P. 55. — This is also very similar to the Erebus kenyte. The pyroxene of the first 

 generation is a titaniferous a?girine- augite, and the base contains abundant leucites. 

 The specimen exhibits striking similarity to the kenyte from Cape Royds examined 

 and analysed by Prior. 



J. 44 (1953). Kenyte, Turk's Head. — This is a dark grey, almost black, somewhat 

 porous lava, porphyritic in large phaneric crystals of felspar with almond shape. These 

 crystals are very dark in colour from abundant inclusions. The hand-specimen is very 

 like the Erebus type just described. 



Texture. — Porphyritic, sempatic, magnophyric in anorthoclase of the first generation. 

 The base is hemihyaline and hyalopilitic. 



Constituents. — The phaneric felspars are of the species of microchne-microperthite. 

 Apatite, magnetite, olivine, and s'girine also occur as representatives of the first 

 generation. The base is quite isotropic under the low power, but the high power 

 reveals felspar microlites, brown grains and belonites whose nature cannot be deter- 

 mined, and yellow glass. 



J. 48 (1957). Vitrophyric Kenyte, Cape Barne. — This rock is very similar to 

 J. 25 from the Skuary. The almond-shaped microcline-microperthites studded with 

 inclusions are of the typical habit and kind. The base is vitrophyric tachylite, and 

 contains corroded phenocrysts of magnetite, olivine, an<J a?girine- augite ; also rods of 

 apatite and microlites of a sanidine-like felspar. (See Plate II, fig 4.) 



3. THE GROUP OF BASIC KENYTES 



General Characteristics. — Phenocrysts, anorthoclase and acid plagioclase; base, 

 phonolitic or tephritic. The hand-specimens of oligoclase kenytes show the tabular 

 plagioclases to possess a planophyric arrangement. 



Excepting for the presence of plagioclase in lieu of microperthite phenocrysts, and the 

 greater abundance of felspathoid, the minerals are the same as those of the acid kenytes. 



The fabric is as variable as in the previous group, but there is a stronger tendency 

 for the base to remain glassy. 



All members of this group contain abundant macroporphyritic phenocrysts of 

 felspar, and smaller amounts of corroded augite, olivine, and magnetite visible to the 

 * National Antarctic Expedition, 1901-1904, Natural History, vol. i, " Geology." 



