808 IEUSINIRVE Sy GA SIEION G TOU. 
Under the microscope the groundmass is seen to be finely 
granitic in structure, and to be composed largely of alkali feld- 
spar in xenomorphic grains, microperthite being rare, with only 
an occasional plagioclase grain. ‘There are also present, some- 
what abundantly, small, clear, rectangular sections of ortho- 
clase. A. little quartz occurs, especially as small interstitial 
grains. Irregular anhedra of colorless or very pale greenish- 
gray diopside are scattered through the groundmass. ‘These are 
often surrounded by a zone of green or bluish-green pleochroic 
hornblende, which does not seem to be secondary. Magnetite 
grains, often surrounded by an amphibole halo, are not uncom- 
mon, and small apatite needles are met with. 
The large black spots consist essentially of an olive-green, 
slightly pleochroic, hornblende. These hornblende areas are 
not continuous, but are made up of more or less rounded spots 
of hornblende, between which lies a granitic mesostasis of feld- 
spar grains like the groundmass. The small hornblende spots 
in each area have their cleavage cracks parallel and extinguish 
simultaneously, so that the structure is micropoikilitic. The 
white borders are of granular feldspar, free from pyroxene, in 
which the small rectangular orthoclase sections seem to be more 
common. They pass insensibly into the surrounding ground- 
mass. - 
A specimen given me by Mr. Sears from Salem Neck (?) is 
similar, but the structure of the groundmass is more trachytic, 
the pyroxene is largely replaced by dark green biotite, and the 
hornblende phenocrysts are much darker in color. The orbicu- 
lar spots are quite ophitic in structure, owing to the tabular 
development of the feldspars. No analysis of these rocks has 
yet been made. 
Henry S. WASHINGTON. 
(To be Continued ) 
