794 HENRY S. WASHINGTON 
la Ila Ta Ila 
Quartz, - - 35.5 30.2 Hornblende, - 2.0 ae 
Orthoclase,  - 5 B32 27.2 Riebeckite,  - Seated UA 
Albite, - - 32.0 D7] Glaucophane, - Biche 2.0 
Anorthite, - = | O25 Sie Accessories, - - 0.5 0.6 
Biotite, - - 163 
Micrographic granite.—On reference to Sear’s geological map 
of Essex county it will be seen that surrounding the granite 
areas and forming a zone between them and the areas of augite- 
syenite and diorite is a belt of micrographic granite. I have 
only a few specimens which represent this facies, the best being 
from Eastern Point, Gloucester, and from near Coy’s Pond, 
Beverly, which were kindly given me by Mr. Sears. These 
closely resemble the granites, but are dark reddish-brown, finer 
grained and with less quartz visible. In thin sections they 
show much the same features as the granites proper. The 
minerals are the same, but quartz is less abundant. The dif- 
ference is mainly in structure. In these rocks a micrographic 
intergrowth of feldspar and quartz is extremely common. The 
quartz here appears as small rounded spots extinguishing simul- 
taneously in patches in the large feldspars. A similar micro- 
graphic structure is described by W. D. Matthew* in soda- 
granite from St. John, N. B. He states, however, that here this 
structure is best developed in the central parts of the mass and 
is lost at the edges. 
In regard to the composition, while no analysis was made 
on account of the decomposed condition of the specimens, yet 
it seems probable, judging from the microscopical examination, 
that these micrographic granites are intermediate in composition 
between the granite proper and the augite-syenite, with a silica 
content of about 70. 
Enclosures in granite-—In the granites of Essex county are 
found in abundance streaks ( Schlieren) and rounded rock masses 
of darker color and of finer grain than the surrounding rock, 
which are also common in granite areas elsewhere. They show 
1W. D. MATTHEW, Trans. N. Y. Acad. Sci., Vol. XIV, p. 205, 1895. 
