344 
The American Geologist. 
December, 1898 
in the iron (FeO) of which the hornblende from Rarkevik 
has 7.38 per cent, more tlian the brown ani])hibole from 
Campton Falls, N. H. 
The ajiorthoclase crystals are lath-shaped parallel to a, 
and show in places a tendency to radial arrangement. They 
are characterized optically by a small angle of extinction 
(the angle a:a=ca.io°), which renders them easily distingnish- 
able from the labradorite of the diabase-porphyry. Polysyn- 
thetic twinning could not be identified — the crystals being ap- 
parently single individuals. 
The anorthoclase decomposes readily to calcite and kaolin. 
An analysis of this feldspar (I) was made from dike 8. 
The material was completely separated by means of the Thou- 
let solution and afterwards exposed to a strong magnetic cur- 
rent whereby many fragments containing inclusions of horn- 
blende or magnetite w^ere removed. For comparison are 
given under II the analysis of anorthoclase from the "Rhom- 
benporphyr" of the Christiania region (Tyveholmen)* and un- 
der III that of murchisonyte from an augite-syenite dike near 
Ula, between Sandfjord and Laurvik, South Norway.f No. IV 
is the analysis of the camptonyte (dike 8), and V and W those 
of enstatite-diabase-porphyry and augite-porphyryte. already 
given on page 341. 
II. 
I. 
SiO^ 57-34 
TiOs 
AI0O3 20.79 
Fe.Os 2.88 
FeO 
CaO 4.27 
MgO 16 
NasO 8.09 
K.O 4- 17 
H=0 2.66 
59-57 
22.69 
2.47 
5-05 
.42 
6.38 
2.50 
1-34 
III. 
64.96 
19.32 
1. 19 
7.26 
5-84 
0.29 
IV. 
20 
V. 
50.76 
VI. 
51-93 
18.13 
8.92 
9.82 
530 
4-34 
1.42 
.69 
100.36 100.36 99.84 100.60 100.22 100.75 
On glancing over the first three analyses it is apparent 
that No. I, although about 3 per cent, richer in alkalies, and 
*See Mugge: Jb. Min., 2, p. 107, 1881. 
fW. C. Brogger: Mineralien der sudnorweg. Angit-syenite. Zeit. 
fiir Kryst. von P. Groth, Leipzig, 1890, Vol. 10, p. 546. 
