The ''Avf/cn'^-Cineiittf Area. — LiKjuer and Jiies, 245 
show quite distinctly on the weathered surface. At times the 
plagioclase almost disappears, leaving a schistose aggregate 
of hornblende and mica. A more or less decomposed phase of 
the gneiss was noticed which consisted of abundant plagioclase 
and mica. Very near the dike a good specimen of the 
"aiigen "-gneiss was obtained and a vein of white quartz out- 
crops just northwest of the road within a liundred feet of the 
dike. 
Dike Ko. 21. The rock is essentiall}^ an aggregate of horn- 
blende crystals with a little mica and varies considerably in 
texture. The color is a dark greenish black, and ])ortions 
near the contacts are considerably decomposed. Garnets are 
extensively developed in the adjoining gneiss. The '• augen "- 
gneiss appears on the same slope and quite near the dike, 
which has probabl}^ branched, as a small isolated outcrop 
occurs by the. road side at the top of the hill. The large peg- 
matite vein on A. Hobby's farm [F) is about three-eights of 
a mile southwest of the dike. 
Petrography op the Area. 
^^ Augen'''' -Gneiss. This consists essentially of orthoclase, 
quartz and biotite. The orthoclase is for the most part pre- 
sent in the shape of " ani/en'" of varying size, with lenticular 
outline. Carlsbad twinning is the rule and microcline some- 
times replaces the orthoclase either wholly or in part. •' Micro- 
clinic" structure may however be developed in the orthoclase 
as the result of dynamic action, as it often has a rather in- 
constant appearance.* Alteration to kaolin is noticed but 
not to any great extent. A few quartz inclusions occur 
in the "augen" and wavy extinction is very marked as the 
result of dynamic action. A section of an *' auge " parallel 
to the twinning plane (No. 11) showed, with reference to the 
basal cleavage, the characteristic small extinction angle (5*^- 
1^) of orthoclase. This section also showed a few small 
Carlsbad twins, of the same species, lying parallel to the 
cleavage planes. These inclusions were usuall}'' surrounded 
*A. Harker, Petrology for Studevts, p. 279. 
J. W. Judd states that " the ^reat mechanical strains, to which rock- 
forming orthoclases have in some cases been subjected, has frequently 
caused them to assume the external angles, the internal structure and 
optical properties characteristic of microcline." Geol. Man. 13], vi. 
243, 1889. 
