Dikes near Portland, Maine. — Lord. 343 
The rock is of a bluish-black color and porphyritic struc- 
ture containing some phenocrysts of serpent inized olivine, be- 
sides a small scattering of purplish brown augite, magnetite 
and pyrite. 
The ground mass consists of idiomorphic brown horn- 
blende, anorthoclase, magnetite and the decomposition pro- 
ducts, chlorite and calcite. 
The liornble7ide crystals are of prismatic development, 
rarely exceeding i mm in length. They have strong pleo- 
chroism in brown and yellow tones ( c>b>a ), and the 
small angle of extinction common to barkevicyte — the angle 
C : c = II degrees in maximo. 
These minute amphibole needles contain in some instances 
the remnants of partially resorbed augite with similar crys- 
tallographic orientation — thus clearly demonstrating them to 
be, in part at least, of paramorphic origin from the augite. 
In order to compare the chemical composition of this 
barkevicitic hornblende with that from Barkevik, large phen- 
ocrysts were extracted from the camptonyte from Campton 
Falls, N. H.,* and analyzed (I). No. II is an analysis of bark- 
evicite given by Brogger from augite-syenite near Barkevik 
(Skudesundsskjar).t 
I. 11. 
Si02 37.80 < 42.46 
Ti02 4.54 \ 
AI2O3 12.89 11-45 
FeaOa 6.14 6.18 
FeO 12.55 19.93 
MnO 0.75 
CaO 13.64 10.24 
MgO 4.10 I. II 
Na20 5.26 6.08 
K2O 3.24 1,44 
100.16 99 64 
Spec. gr. 3.47 Spec. gr. 3.43 
No. II is seen to contain 6.39 per cent. MgO+CaO and 
1.80 per cent. K2O less than No. I, but the main difference Hes 
*This material was obtained from a specimen of the original dior- 
yte of Hawes in the collection of the U. S. National Museum. 
fSee P. Hintze: Handb. der Miner. Leipzig, 1893, p. 1257. 
