106 PETROLOGY OF THE ALKALINE ROCKS 



transversely (species of cossyrite) ; idiornorphic grains of magnetite; apatite and 

 zircon needles and a little interstitial dark glass. The base is therefore like the 

 trachyte of Observation Hill, Hut Point, though the brown hornblende is most 

 nearly allied to that of the Cape Crozier trachyte described by Prior (cf. Table I, 

 D and E, p. 98). 



J. 25 (1934). Vitrophyric Kenyte (Analysis, Table II, C, p. 110), same locality. — Hand- 

 specimen, reddish. 



Texture. — Coarsely porphyritic, dopatic, megaphyric with vitrophyric fabric, the 

 base being almost holohyaline. 



Composition. — The chief constituents are lozenge-shaped anorthoclase (microcline 

 microperthite) phenocrysts, some a?girine phenocrysts (Plate II, fig. 4), and red glass. 

 The latter constituent fills corrosion cavities in the phenocrysts (Plate II, fig. 3). 

 The other phaneric minerals are corroded lumps of magnetite and smaller grains of 

 red iron ore. The red glassy base contains some microporphyritic laths of anorthoclase 

 and non-refracting cryptocrystalline needles (belonites) immersed in the reddish-yellow 

 tachylitic matrix. 



J. 5 (1712). Kenyte, same locality. — This rock is similar to J. 47, but more 

 coarsely grained, quite holocrystalline, and contains some secondary epidote 

 replacing the original aegirine-augite to some extent, and also aggregates of dusty 

 soda hornblende. Interstitially colourless idiornorphic material consisting of nosean, 

 and full of riebeckite inclusions, is present. 



For Analysis see Table II, B, p. 110. 



J. 40 (1948). Kenyte, same locality. — Very similar to J. 47. It differs from J. 47 

 chiefly in the greater abundance of olivine phenocrysts, and in the greater alkalinity 

 of the pyroxene, which is here a true segirine. The base is holocrystalline 

 stahlenkornig. It differs from J. 47 in the absence of cossyrite- like hornblende, and 

 the presence instead of scattered grains of a purplish opaque, very pleochroic 

 hornblende, which changes colour from dark blue opaque to purple on sections 

 parallel with the length, and reddish-brown opaque on sections at right angles to the 

 length. This amphibole is probably a kataphorite closely allied to riebeckite. 



Flakes of haematite are abundant in this rock. This specimen is clearly of a more 

 alkaline type than those already described. 



Photo. Plate II, figs. 1 and 2. 



J. 63 (1962). Specimen P. 103. An erratic from Cape Royds. — Similar to the 

 foregoing. Kenytes of the acid type were also obtained on Mount Erebus, at Cape 

 Barne, and as erratics at Cape Royds. Many Cape Royds erratics correspond closely 

 with the Skuary types. Decomposition of the pegirine to epidote and the formation 

 of secondary magnetite were noticeable features. 



The typical Mount Erebus and some Cape Royds kenytes are different from those 

 just described {see Plate III, fig. 1 ). They occupy a position intermediate between 

 the Skuary and the Turk's Head types. The phenocrysts are those of the acid kenytes, 

 and the base is that of the basic kenytes and tephrites. The phenocrysts consist of 

 the characteristic rhomben felspars, sparing olivine, pyroxene, ilmenite, and sphene. 



The base is hypocrystalline, microporphyritic serial, hyalopilitic, and consists of 

 miniphyric phenocrysts of leucite (with characteristic outlines, central and marginal 

 inclusions of dusty magnetite), microlites of felspar, brown glass, and colourless isotropic 

 glass (possibly of the composition of nosean, sodalite, or analcite). The brown glassy 



