64 TRANSACTIONS OF THE [FEB. 1, 
part of the middle third elaeolite porphyry appears, and forms a 
most beautiful example of this rock. It may come from dikes, as 
no actual exposures are available. Further south a basic holo- 
crystalline rock comes in which is exposed in place ; and, as subse- 
quently shown, contains less silica and more biotite than the typical 
svenite. But on the extreme. south where the highway crosses the 
dike, the rock is much like that on the north. It is, however, 
greatly decomposed, and fresh, firm pieces are hard to find. The 
basic lamprophyric rocks outcrop on the east, at the several points 
shown on the map, and extend to a distance of several miles with 
isolated outcrops. 
The typical characteristic elaeolite-syenite of the north is the rock 
described by Emerson, and little remains to be added to his diag- 
nosis. It outcrops as small hillocks in the woods, which are 
covered with great boulders, loosened by disintegration. The 
commonest rock consists of large pinkish orthoclase crystals, which 
may, in the coarsest variety, be two inches long, and are twinned 
on the Carlsbad law. In the interstices of these the elaeolite and 
aegirine are chiefly found, and far less often they occur in the slide 
as inclusions in the feldspar. The orthoclase also appears as small 
rod-shaped, once-twinned crystals associated with the elaeolite. 
The elaeolite is allotriomorphic in irregular masses. Emerson 
notes in addition a rare and earlier generation of smaller idiomorphic 
crystals. The elaeolite is largely changed to cancrinite, which ap- 
pears in mosaics of irregular individuals, and is the only alteration 
product which I have detected. No zeolites appear. The cancrin- 
ite seems to have been overlooked by Emerson. Sodalite is not 
infrequent, and forms, at times, an inclusion of hexagonal outline 
in the orthoclase. Aegirine is associated with the elaeolite and 
forms small prismatic crystals. In the slides they are a fraction of 
a millimeter in diameter and several times as long. They are 
seldom, if ever, terminated, but have irregular ends. The pleo- 
chroism is strong, being two closely similar shades of grass-green 
along the axes of elasticity, which nearly correspond with axial ¢ 
and b (=a and b of Rosenbusch, or ¢ and b of Descloizeaux re- 
spectively), and brownish-yellow on axial @ (=c of Rosenbusch 
and a of Descloizeaux). An optic axis shows plainly in sections 
near OP (001), and affords a negative figure with the quarter undu- 
lation plate. Several large crystals were picked out of a decom- 
posing syenite, and the prism angle was measured on a Fuess No. 
II. goniometer. The faces were not very good, and necessitated 
the employment of the Websky delta ocular. Three of the best 
readings were 87° 14’, 87° 12’, 87° 33’, corresponding closely 
with the 87° usually given for aegirine, and with the 87° 13/ 
(92° 87’) given by Emerson. The orthopinacoid is also present. 
A specimen was found in which the aegirine prisms reached a length 
of an inch or more, and had a marked parallel arrangement with 
elongated orthoclase crystals, like a very coarse flow structure. The 
same thing has been remarked by Brégger in Norwegian exposures 
——— v7 
ee 
