KENYTES. — PHONO L1TIC TRACHYTES. 
113 
The olivine-phenocrysts occur very sparingly, and are generally less than 1 mm. 
in diameter ; they are clear and colourless, and often contain inclusions of apatite and 
magnetite. They are generally of irregular and sometimes of perfectly round outline : 
oidy occasionally is one seen with distinct crystalline shape. Intergrowths of augite 
and olivine occur, and in one case augite was seen to be enclosed in olivine. 
Augite-phenocrysts occur even more sparingly than the olivines. They are 
generally without distinct crystalline outline, and consist of a pale-gray or brown 
augite having angles of extinction of over 40°. In a specimen (837) of glassy kenyte 
from a moraine at the “mouth of 2nd Alpine Valley,” in Discovery Gulf, the augite- 
phenocrysts are in larger amount, and attain a length of 2 to 3 mm. : usually they are 
less than 1 mm. in length. The augite of the ground-mass occurs generally in small 
prisms of a pale-gray to green colour, but in some specimens this is replaced to some 
extent by grass-green segirine-augite. 
Apatite is fairly plentiful in these rocks ; often it is of a pink colour, and dense 
with dark inclusions arranged in lines parallel to the length of the needles. 
A chemical analysis of the leucite-kenyte (818) from Cape Royds gave the 
following result under I*, as compared with that of a kenyte from Mount Kenya 
under Ilf, a leucite-kenyte (“ leucite-rhomb-porphyry ”) from Kibo (Kilimandjaro) 
under II If, and a nepheline rhomb-porphyry from Vasvik, Norway, under IV:— 
I. 
Ia. 
II. 
III. 
IV. 
(Cape Royds.) 
Mol. ratios. 
(Mt. Kenya 
•) 
(Kibo.) 
(Vasvik.) 
SiO., 
56 • 09 
•929 
53-98 
53-44 
56-04 
TiO., 
= 
1-23 
•015 
0-57 
0 1 69 
0-65 
A1 2 0 3 
= 
20'7i) 
•203 
19-43 
20-39 
21-50 
Fe 2 0 3 
= 
1-54 
*010 
4-39 
4-22 
1 -06 
FeO 
= 
3-84 
•054 
2-05 
1-76 
3-28 
MnO 
= 
0-05 
0-26 
trace 
CaO 
= 
3-18 
•057 
2-04 
2-13 
2*42 
MgO 
= 
1-26 
•031 
1-07 
1-12 
1-12 
Na.,0 
= 
7-33 
•118 
8-81 
8-70 
8-39 
K.,0 
= 
3-91 
•041 
5-27 
5-75 
5 " 03 
PA 
= 
0-38 
•003 
0-30 
0-49 
01 
= 
0-17 
H.,0 at 110° 
= 
0-19 
0*13) 
0-97 
0-67 
11. ,0 above 110° 
= 
0-39 
1-663 
SO, 
0-22 
Zr0 2 
0-27 
100-35 
99-96 
100-21 
100-16 
Phonolitic 
Trachytes 
(Trachydolerites) 
AND 
PlIONOLITES. 
Most of the rocks which are here included under the name of trachyte are of a 
somewhat basic type, and so closely related in chemical composition to the preceding 
alkaline basalts or kenytes that some hesitation is felt in separating them ; with the 
kenytes they might all be classed under the trachydolerite group of Rosenbusch. 
These trachytes are pale ash-gray compact rocks ; but weathered specimens (in 
* For discussion of analyses, see p. 119. 
t Prior, Mineralogical Magazine, 1903, vol. xiii, p. 247. 
| Finclsh, l.c., p. 392. q 
vol. i. 
