320 DR. JOHN S. FLETT: PETROGRAPHICAL NOTES ON THE PRODUCTS OF 
judge by the optic axial angle, which in this group of minerals varies with the 
percentage of iron present, the St. Vincent hypersthene is not quite so ferriferous as 
that of Martinique. 
I. 
II. 
III. 
IV. 
V. 
Si0 2 
47-15 
45-0 
44-17 
50-54 
43-26 
TiOo 
0-90 
0-3 
— 
— 
0-29 
alo 3 
22-30 
32-5 
35-06 
3-94 
13-15 
Fe 2 0 3 
2 • 22 
0-2 
— 
0-90 
2-27 
FeO 
G • 93 
3-0 
0-58 
17-08 
10-50 
MgO 
5-15 
0-7 
0-57 
25-71 
15-06 
CaO 
12-30 
17-1 
18-84 
1-82 
12-11 
NaoO 
1-81 
0-8 
1-21 
0-79 
3-49 
k 2 o 
0-35 
0-2 
0-43 
0-55 
0-57 
p 2 "o 5 
0-19 
— 
— 
— 
— 
h 2 o 
1-00 
\ 
0-59 
— 
0-21 
100-20 
100-8 
101-45 
101-33 
100-91 
I. Dioritic enclosure (anorthite-hornblende rock) Chateaubelair (anal. Pisani, cited from Lacroix, ‘ La 
Montague Pelee,’ p. 598). 
II. Troctolitic enclosure (anorthite-olivine rock), St. Vincent (anal. Arsandaux, ibid., p. 598). 
III. Anorthite from an anorthite-olivine block from St. Kitts (anal. Fees, ‘ Zeits. Kryst.,’ XXXVII., 
p. 459, 1903). 
IV. Hypersthene from an anorthite-olivine block from St. Kitts (ibid.). 
V. Hornblende from an anorthite-olivine block from St. Kitts (ibid.). 
Norites , Quartz-Norites [Andes-Norites). 
These are less common than the anorthite-olivine blocks, hut are of interest because 
they represent a type known also in Martinique and some of the other islands and of 
wide distribution among the volcanoes of the Andean or Pacific facies. # They 
consist of plagioclase, augite, and hypersthene, and are rather fine grained and 
holocrystalline, or contain a little glass. Larger phenocrysts of plagioclase may occur, 
but are scarce. Their felspars, in contrast to those of the anorthite-olivine blocks, 
are invariably much zoned and are often idiomorphic. They show Carlsbad, albite 
and pericline twinning in great perfection. The centres of different crystals proved to 
contain 80, 75, and GO per cent, of anorthite; bytownite is evidently the prevailing 
type. These centres are corroded and surrounded by more acid zones succeeding one 
another in great numbers; more and less acid bands may alternate repeatedly. The 
margins are often andesine with 35 per cent, anorthite, but oligoclase (20 per cent. 
* Rosenbusch, H., ‘ Mikroskopische Physiographic,’ B. II., p. 292 (1907); HOGBOM, A. G., “ Zur 
Petrographie der Kleinen Antillen,” ‘Bull. Geol. lust. Upsala,’ vol. vi., p. 214 (1905). 
