G. T. PRIOR. 
106 
basalts, Castle Rock (431, 319), Crater Hill (341), Harbour Heights (323, 325, 3GG), 
aucl between the Gap and Horseshoe Bay (G5G). 
Specimens of the more glassy limburgite-type were obtained from the same 
localities, and also from Turtle Back Island (449) and Dailey Islands (510). 
The basalt (553) from Cape Armitage has microscopic characters precisely similar 
to those of the basalt (65G) from between the Gap and Horseshoe Bay, and is probably 
the prolongation of that rock mentioned on p. 12 of the Report on the Field-geology. 
The bombs found on Harbour Heights (3G7, etc.) consist of olivine-basalt like that 
of the lavas. 
The results of the analyses both of the hornblende-basalt and of the olivine-basalts 
indicate that nepheline is present in these rocks, either in the interstices of the felspar- 
laths or potentially in the glassy base. Generally it could not be recognised with 
certainty under the microscope, but in a basalt (718) from the scree-slope below 
Cathedral Rocks could be distinguished in the ground-mass small colourless patches 
of isotropic analcite (?), and of doubly -refractive nepheline of which the refraction 
was about the same as that of Canada balsam. This rock, which showed under the 
microscope small phenoci’ysts of pale-purple augite and rounded olivines in a ground- 
mass of felspar-laths, augite and magnetite, has a much closer relationship to the 
recent basalts of the Ross Archipelago than to the dolerites of the Ferrar Glacier. 
Analcite is probably present in some of the other basalts which show small amounts 
of colourless isotropic material in the base, e.g., specimens from Cape Adar-e (49), from 
Little Razor Back Island (471), and from the top of Castle Rock (319). 
As a connecting link between the olivine-basalts with no porphyritic felspars and 
the alkaline rocks (kenytes) with porphyritic anorthoclases, to be described in a later 
Section (p. 110), are a few specimens of basalt showing conspicuous phenocrysts of felspar. 
These come from Black Island (593), the debris-heap off Minna Bluff (619), 
Inaccessible Island (805), Turtle Back Island (484, a boulder), and Cape Barne (814). 
They show numerous phenocrysts of clear glassy felspar in a ground-mass of felspar- 
laths, magnetite in grains and rods, pale-purplish augite and a little olivine. The 
rocks resemble the kenytes, but the felspar-phenocrysts have not the characteristic 
shape of the anorthoclases ; instead, they consist of an acid labradorite or andesine, 
having a specific gravity of 2 ‘68, and showing an extinction on & (010) of about 
16°. In the case of the boulder (484) from Turtle Back Island, these phenocrysts are 
so flattened that the rock appears to be composed of alternating white and black 
layers. 
Coarse-grained Felspathic and other Nodules in the Basalts. 
A striking feature in the basalts of the Ross Archipelago, especially in those of 
limburgite-type, is the number of included coarse-grained nodules. These were found 
plentifully, not only enclosed in basalts but also in loose lumps, in the neighbourhood 
of Winter Quarters. 
