NOTES ON ANTARCTIC ROCKS. 475 
They are too minute to be certain of pleochroism. In addition 
to these there is much magnetite dust. 
This rock ought perhaps to be classified as a trachytic andesite 
owing to the number of apparently monoclinic felspars present. 
The amount of glassy base present renders its nomenclature a 
matter of uncertainty which can only be settled by chemical 
analysis for which there has not been time up to the present. 
Vesicular Andesite Glass, No. 13. 
This is a highly vesicular fragment which on examination proves 
to have many points in common with the glassy andesite No. 11, 
and may well be considered as a portion of the same flow. The 
porphyritic constituents are quite similar to those in No. 11, with 
the exception that we have here some hornblendes preserved with 
a ring of opacite granules round them, while in No. 11 the horn- 
blende has practically completely disappeared, The lath-shaped 
felspars are not so numerous, but are still for the most part simply 
twinned. The base is faintly coloured and somewhat more glassy 
while the incipient felspar plates are not noticed. 
The minute augite crystals are perhaps quite as numerous as 
in No. 11, but are even smaller while the magnetite and opacite 
dust is more diffused. 
Basaltic Andesite (No. 6). 
In the mass fine-grained, very dark grey in colour, with but 
few porphyritic crystals. Sp. gr. 2:78. 
Th sections the ground mass is eryptocrystalline, and contains 
a dust of magnetite and minute augite granules. Above this in 
86 scale of crystallization is a crop of forked triclinic microlites, 
Siving extinction angles approximating to labradorite. There 
are also many small square and rectangular sections of felspar, 
most of which show only simple twinning. 
Some large crystals of magnetite are present, and a number of 
ee sized’ yellowish brown augites. One or two grains of 
olivine were noticed enclosed in augite. There are also some 
