i ee ee i a on 
1892. ] NEW YORK ACADEMY OF SCIENCES. 67 
with a much more prismatic development of the elaeolite in the 
ground mass. 
An analysis yielded the results in column I. Column II is of 
the elaeolite porphyry from Magnet Cove (J. F. Williams, Igneous 
Rocks of Arkansas, p. 261). 
I. II. 
Loss F : P 2 Ts 2.06 
0 Re eee ae ee 44.50 
eee eean Wrob aia fe kee 1.40 
PRG eee Ph 34 22.96 
mee rach ae Mate PC 6.84 
Ome eek AGS 8.65 
Meee Ne ey oko” Gerben 1.65 
K,O SN Wis eee een rt 4.83 
es ae Met ede foray eg LIBS 6.70 
98.92 99.59 
The rock is thus more basic than the syenite, and illustrates a 
change to a more basic composition as the south end of the dike is 
approached. It is very basic also when considered as an analogue 
of phonolite, and is nearer the theralites. With some variations it 
has other close points of correspondence with the analysis quoted 
by its side. 
The sections of the New Jersey phonolitic or tinguaitic specimens 
have been compared with a set which were made from a suite of the 
corresponding Brazilian varieties which are in the rock collections of 
Columbia College. They were presented some years ago by Mr. 
Derby. The resemblance is most striking and indeed so close that 
the slides might readily be confounded. The New Jersey examples 
show no tendency to cleave in thin plates like ordinary phonolites 
and like some of the Brazilian examples, but break in angular frag- 
ments; hence the name elaeolite-porphyry seemed appropriate and 
was employed above. The correlation of many types in the two 
exposures is remarkable. 
Still further south, at a point half-way between the last and the 
southern extremity of the dike, a prospect hole has been blasted by 
some one in the top of a conical hillock. It has opened up a cavity 
some few feet deep, and brought out a quantity of perfectly fresh 
material. The rock is-rather finely crystalline, dark in color, and 
very tough. It looks like a fine mica diorite, and has a great pro- 
portion of dark silicates. The sections exhibit elaeolite, orthoclase, 
aegirine, biotite, titanite, many minute zircons and apatites. Ex- 
cept the minute inclusions, all the components are allotriomor- 
phic. The aegirine and biotite especially appear in shreds and small 
irregular masses. No cancrinite is present, and from this fact, as 
the rock is perfectly fresh, the conclusion is unavoidable that the 
cancrinite to the north is secondary and derived from the elaeolite. 
Careful search was made for plagioclase in the slides, yet none 
