306 B. K. Emerson—Dyke of Elaolite-syenite in New Jersey. 
can be seen toward the surface of the rock to be changed for a 
part or the whole of their length into a greenish black, fibrous, 
hornblendic mineral apparently arfvedsonite. 
The third constituent, orthoclase, occurs in elongated Carls- 
bad twins up to 80™ in length; in a single instance three crys- 
tals are twinned together. They are of brilliant luster, and of 
the same flesh color as the elwolite in the fresh rock, while 
toward the surface they are whitened, and there closely resem- 
ble the feldspar of the Brevig zircon-syenite. They are scat- 
tered in the rock somewhat distantly, so that in three sections 
no feldspar appeared. The crystals enclose rounded masses of 
eleolite as well as crystals of zgirite, often so thickly crowded 
as to give the feldspar a pegmatitic appearance. 
itanite occurs in minute crystals quite abundantly. The 
) 
often brightly iridescent. No trace of triclinic feldspar or of 
hypersthene could be foun 
“High up along the crest of the ridge, perhaps fifty rods west 
of the point where the specimens were obtained which fur- 
nished the material for the above description and for micro- 
scopical study, the rock is much coarser grained, more loosely 
granular and decomposed, failing readily to a mass of coarse 
grains under the hammer. 
The proportion of elwolite is here much less, and the only 
additional mineral found in this coarser variety was a glossy 
black mica, which gives all the blowpipe reactions of astro- 
phyllite, but it may be a biotite containing much manganese. 
er the microscope by far the greater portion of the section 
is eleolite, with scattered crystals of wgirite and titanite. The 
eleolite presents itself in three forms, quite distinctly demarked : 
(a) as distinct crystals, stout hexagonal prisms with end faces, of 
much the same appearance and properties as in tne more moa- 
ern nepheline rocks. These crystals are rare. The cleavage 
is more perfect and delicate than in the remainder of the elzeo- 
lite in which they are embedded, and as a result they are only 
slightly decomposed. They are quite free from enclosures. 
The second form (6) appears in somewhat larger, aggregated, 
and more imperfect crystals, in which the basal, prismatic 
and pyramidal cleavages are ruder and more open, and the erys- 
tals much more decomposed. Flakes of a green hornblendic 
mineral, probably arfvedsonite, appear as enclosures parallel 
to the three cleavages, Finally it occurs (¢) filling up the 
interstices of the other two forms like the quartz of a granite, 
and swarming with minute acicular microlites, especially in the 
recesses made by neighboring crystals of earlier formation. 
This portion has a less distinct cleavage and is less decomposed. 
