G. T. PRIOR. 
114 
which the augite of the ground-mass, together, apparently, with some of the magnetite, 
has been altered, with development of orange-yellow epidote) are of a pale-yellow or 
pink colour. They differ from the kenytes in showing either no phcnocrysts of 
anorthoclase or only few and small ones. 
Those which approximate most closely to the kenytes show under the microscope 
an occasional small rounded phenocryst of olivine and augite in a ground-mass consisting 
of a mesh of felspar-laths, with interstitial irregular grains and shreds of dull-green 
augite, needles of pleochroic (yellow to dull-green) gegirine-augite, and only a few 
magnetite grains. The felspar-laths are not sharply defined, and are often associated 
with more platy felspars; they have a refraction not greater than clove oil ( 1 • 538), 
and consist mainly of anorthoclase. That nepheline is present in these rocks is 
probable, although it cannot with certainty be recognised under the microscope. 
To this type belong specimens 804, from Inaccessible Island, and 473, from Little 
Razor Back Island. 
The specimens collected by the * Morning ’ from Scott Island and a trachyte (188) 
from the top of the 900-ft. knoll at Cape Crozier are of similar character, but show 
no porphyritic olivines and augites in the thin slices examined. The rock from Cape 
Crozier is of a lighter-gray colour and of more salic character than the specimens from 
Scott Island ; it shows the peculiar surface-shimmer, due to the parallel arrangement of 
the platy felspars, which is so characteristic a feature of many of the alkaline rocks 
of Norway (solvsbergites) described by Brdgger.* 
A coarse-grained inclusion in this trachyte (188) consists of an aggregate of stout 
felspar-prisms, with some pleochroic (yellow to grass-green) gegirine-augite and a little 
cossyrite-like hornblende showing pleocliroism from reddish-brown for vibrations across 
the length to black for those along the length ; the felspars are partly oligoclase with 
symmetrical extinctions of about 8°, and partly anorthoclase. 
The results of chemical analyses of the rock from Scott Island, and of the trachyte 
from -Cape Crozier (188) are given under I and II respectively.! They show the close 
chemical relationship between these rocks and the leucite-kenyte, the analysis of which 
is given on p. 113. 
I. 
Ia. 
II. 
IlA. 
(Scott Island.) 
Mol. ratios. 
(Cape Crozier.) 
Mol. ratios. 
SiO„ 
= 
55-93 
•926 
57-95 
•959 
Tio; 
= 
0-64 
•008 
0-40 
•005 
Ab0 3 
= 
19-61 
•192 
20-43 
■200 
Fe.A 
= 
1-75 
•on 
3-43- 
•022 
FeO 
= 
G-32 
•090 
1-35 
•020 
MnO 
= 
0-13 
0-07 
CaO 
= 
3 ■ 53 
•063 
1-90 
•034 
MgO 
= 
0-50 
•013 
0-26 
•006 
Na.,0 
= 
7"75 
•125 
8-32 
• 134 
K,0 
= 
3-67 
■039 
5-96 
•063 
P.,0, 
= 
0-12 
•001 
0-07 
•001 
ILO at 110° 
= 
o-io 
0-23 
TLO above 110° 
= 
0-19 
0 • 39 
100-24 
100-76 
* Broggcr, Eruptivgesteine dcs Kristianiagebietes, 1894, I, p. 76. 
f For discussion of the analyses see p. 119. 
