34 I'll' A nit rial n Geologi8t. July, 1893 
The writer's analysis of dike 1 is shown in column I. For 
comparison, analyses of ;i bostonite by Kemp* and the ker- 
atophyr described by Sears are shown in columns II and 
1 1 1 respectively. 
I. 
SiO 
G7.it; 
FeO 
14.53 
Pe 2 o 3 
4.17 
MnO 
CaO 
1.26 
MgO 
0.41 
K 2 ° 
6.10 
Na 
5.55 
Loss 
1.10 
II. 
III. 
02.22 
65.66 
19.17 
20.05 
trace 
3.39 
trace 
0.13 
1.44 
0.67 
trace 
0.18 
5.926 
6.98 
5.374 
6.56 
2.33 
0.41 
100.28 99.85 100.64 
Plagioclase and augite with varying amounts of olivine 
make up the essential part of the rock. Magnetite is an 
abundant accessory from the alteration of the dark silicates 
and- often assumes beautiful arborescent forms. The plagio- 
clase is of the usual lathe shape and shows frequent twinning. 
Augite occurs both idiomorphic and in irregular grains. 
The common forms of the idiomorphic crystals are xP(llO), 
ocPgc'(OTO), and ooPao (100). In some of the dikes the aug- 
ite predominates as the dark silicate, and the rock approaches 
more the augite- porphy rite type of dikes. It is of the usual 
rose tint, and the deeply colored crystals show a slight 
pleochroism. The large well formed crystals exhibit a beauti- 
ful zonal structure and the zonal walls surround a granular 
core of slightly decomposed material. Twinning is rare, 
but in a few cases occurs parallel to the clinopinacoid ocPoc 
(010). Extinction angle is about 43°. 
Dikes 2 and 3 are notably different in respect to the kind 
of green silicate present. The two dikes present the same 
ophitic structure, but in the former the green mineral is 
mainly epidote, with minor amounts of chlorite and little, if 
any. olivine. The epidote possesses a marked pleochroism 
from green to yellow in incident light, and shows strong 
double retraction and brilliant colors in polarized light. It 
appears to he a final alteration product of original augite. 
*Kemp, J. F. & Marstere, V. F. Trans. N. Y. Acad. Sci., xi, 1891, p. 13. 
