1894. ] NEW YORK ACADEMY OF SCIENCES. 211 
the latter. The augite is of a brownish pink color, with faint 
pleochroism. The ordinary prismatic cleavage is distinct, and 
twinning is rather common. There is an abundance of inter- 
positions closely resembling those of the feldspar, though often 
attaining a somewhat larger size and more distinct rod-like form. 
They are usually in rows parallel to a pinacoid, but sometimes 
parallel to the prism. The augite often shows a conspicuous 
amount of bending, the cleavage cracks being greatly curved, 
while there is a correspondingly strong undulatory extinction. 
Occasionally a piece of the mineral has a fan-like appearance, with 
radiating cracks and cleavage lines in concentric curves, across 
which a dark band swings like a pendulum upon turning the 
stage back and forth. The appearance is very like that “of a 
spherulite, but is confined to a single individual of the augite. 
Alteration yields a pale green pleochroic chlorite, or a nearly 
opaque, yellowish-brown aggregate, probably serpentinous. In 
a very few sections there is a small quantity of green hornblende, 
apparently derived from the augite. 
Olivine is an important constituent of a part of the dikes, is 
present in small amount in others, and is absent from about 
half. It occurs generally in irregular grains, rarely with crys- 
tal outline. It is nearly or quite colorless and is readily distin- 
guished by its high mean index, strong double refraction, par- 
allel extinction and imperfect cleavage. The freshest pieces 
show slender rod-like interpositions, parallel to the cleavage, 
which, as alteration progresses, increase in size and become ir- 
regular in outline. The final result of the process is the com- 
plete replacement of the olivine by an opaque mass colored by, 
and largely made up of, hematite. The grains of olivine, whether 
fresh or altered, are surrounded by a narrow band composed of 
radiating plates of a colorless mineral with quite strong refrac- 
tion. It is not possible to get any very clear evidence of the 
character of this mineral with crossed a but it seems to 
have an inclined extinction of rather low angle. From this it 
is probable that the mineral is tremolite. It is evidently not 
the result of simple alteration of the olivine, but is of the nature 
of a reaction rim between this mineral and the feldspar. 
Magnetite is an abundant constituent, being present in large 
irregular grains, sometimes with a slight skeleton structure. 
The mineral is regarded as magnetite because readily soluble in 
hydrochloric acid and strongly attracted by the magnet. But 
the titanium reaction with H, O, and the presence of some leu- 
coxene indicate that the magnetite contains titanium, or that 
there is also ilmenite present. The latter conclusion is ren- 
dered very probable by the approach to hexagonal outline often 
