KENYTES OF MOUNT EREBUS. 
Ill 
rocks of Mount Terror and Winter Quarters by their numerous and large (2-3 cm. in 
length) porphyritic lozenge-shaped crystals of anorthoclase, resembling those of the 
well-known rhomb-porphyries of Norway (see Fig. 62). They are almost precisely 
identical in characters and chemical composition with the kenytes of Mount Kenya,* 
and the description recently published by Dr. Finckh of the rhomb-porphyries 
(kenytes) of Kilimandjaro f could be followed almost word for word in an account of 
these Antarctic rocks. They are alkaline basalts or trachydolerites (Rosenbusch), 
intermediate in type between ordinary basalts and phonolites. 
In colour they vary from dark-gray, to nearly black in the more glassy varieties. 
Under the microscope they show, besides the large phenocrysts of anorthoclase, small 
rounded olivines and pale-gray or brown to pale-purple augites sparingly distributed. 
In different specimens the ground-mass varies in texture, and to some extent 
also in mineral composition. In some (812 
from the Skuary) it is quite holocrystalline, and 
consists of a trachytic mesh of interlacing fel- 
spar-laths (mainly anorthoclase) with interstitial 
shreds and small prismatic crystals of a pale- 
green augite and grains of magnetite ; in 
others (464 from Tent Island) it is a brown 
glass, dense with magnetite in grains or rod-like 
skeleton-crystals, but showing in clearer pale- 
brown streaks minute microlites of felspar and 
augite. In the boulder 447 from Turtle Back 
Island, the glassy base is confusedly spherulitic 
with minute magnetite - grains arranged in 
radiating wavy lines. In Fig. 63 is represented 
a spherule with the black cross as seen between 
crossed nicols. The glass in the base of specimen 541 from the slope of Mount 
Erebus is almost colourless, but in parts is rendered nearly opaque with fine 
dusty magnetite ; in the clear brown glass, however, which is included in the 
anorthoclase-phenocrysts of the same rock there has been no separation of magnetite 
except round the edges, from which project long, colourless, needle-like microlites 
of augite. 
O 
Fig. 63. — Spherule with Magnetite, in 
Glassy Kenyte, prom Turtle Back Island. 
(Magnification, 200 diam.) 
The rocks from Cape Royds (818, 820) present a distinct variety characterised by 
the presence of leucite. They show large phenocrysts of anorthoclase and, very 
sparingly, small rounded olivines, like those in the other kenytes, but contain in the 
ground-mass fairly numerous, small, rounded, isotropic crystals of leucite having- 
characteristic central and marginal inclusions of the magnetite and augite of the base (see 
Plate VIII, Fig. 3). These rocks are therefore similar to the leucite-rhomb-porphyries 
* Gregory, Quart. Journ. Geol. Soc., 1900, vol. Ivi, p. 205. 
f Finckh, Festschr. z. siebzigsten Geburtstage von Harry Rosenbusch, 1906, pp. 373-397. 
