64 TRANSACTIONS OF THE [PEB. 1, 



part of the middle third elaeolite ])orphyry 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 

 syenite. 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 the}^ 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 c 

 and h (= n and b of Kosenl)usch, or c and b of Descloizeaux re- 

 spectively), and brownish-yellow on axial a (= C of Rosenbuseh 

 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 Websk}^ delta ocular. Three of the best 

 readings were 8t° 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 i)arallel arrangement with 

 elongated orthoclase crystals, like a very coarse flow structure. The 

 same thing has been remarked by Brogger in Norwegian exposures 



