66 TRANSACTIONS OF THE [FEB. 1, 
resembles a secondary filling of a crack, as the plates lie across the 
long direction of the flow lines. A short distance from the contact, 
however, the dike becomes the coarsely crystalline syenite and extra 
rich elaeolitic portions could only be extremely local. 
I searched carefully and in many places for endialyte or eucolite, 
but none appeared. Professor Rosenbusch notes small crystals of 
a questionable mineral in a slide of a finely crystalline variety sent 
him, as perhaps one of these. One or the other may be discovered 
in the future. In the writer’s opinion it would not ‘be worth while 
to make separate varieties of the rocks with aegirine and of those 
with biotite, as there is hardly a pure specimen of either. Experi- 
ence in this occurrence thus corroborates the general conclusions 
laid down by Rosenbusch about the subdivisions of the elaeolite- 
syenites. Small hornblende crystals regarded as arfvedsonite are 
noted by Emerson, but they have escaped my attention if present 
in my slides. 
At the middle point of 4 C on the map the character of the dike 
changes, as is indicated by the float fragments, for no actual expo- 
sures occur. Porphyritic facies appear, and an excellent elaeolite- 
porphyry was found. By an odd coincidence the same kind of rock 
was discovered at almost the same time by the late Dr. J. Francis 
Williams, with whom the writer was in active correspondence, in 
Saline Co., Arkansas, making the first American records of this 
rare rock species simultaneous in two widely separated regions 
(see Igneous Rocks of Ark., p. 149). The Beemerville porphyry 
is dark greenish in color, and has great hexagonal phenocrysts of 
elaeolite : up to an inch in cross section. The slides show a ground 
mass perfectly typical of the dikes recently called tinguaite by 
Rosenbusch, from the Brazilian occurrences. They furnish a strue- 
ture among the elaeolite dike rocks closely analogous to the phono- 
lites of the effusives, and the dikes were indeed called phonolites by 
Derby, their original discoverer... The ground mass consists essen- 
tially of elacolite surcharged with microscopic aegirine needles. 
Orthoclase is present and many erystals of a very peculiar pyroxene. 
This is light yellow in color, with a pleochroic change along axial b 
toa pinkish Shade. It is idiomor phic, and has an ‘extinction that 
may reach 44°. Professor Rosenbusch estimates the angle of the 
optic axes at about 55°. An optic axis emerges not oreatly inclined 
to the basal section. 
Closely associated with the pyroxene is a reddish-brown nearly 
isotropic mineral, of high index, that is much like perofskite. A few 
shreds of biotite are also seen. 
Another porphyritie rock occurs along this portion of the dike, 
which lacks the large phenocrysts of elaeolite. It has, however, 
others of feldspar, and in the slide shows the same tinguaitie base 
10. A. Derby, On Nepheline Rocks in Brazil with Special Reference to the 
Association of Phonolite and Foyaite, Q. J. G. S., August, 1887. 
