PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 55 



highly irregular grains and prisms, and also accompanying a 

 colorless diopside, of which it seems to be an alteration prod- 

 uct. The hornblende in this case is not rarely bluish-green, 

 and apparently contains some soda. The pyroxene, which is 

 not abundant, is a colorless diopside, usually in large crystals, 

 and nearly always altered more or less to the green hornblende. 

 It sometimes shows such brilliant polarization colors as to sug- 

 gest olivine, but the fine straight cleavage lines and the oblique 

 extinction prove it to be a monoclinic pyroxene. Small flakes 

 and stout tables of a greenish yellow biotite are quite common. 

 Titanite, often showing lozenge-shaped sections as well as in 

 irregular grains, is abundant. Small grains of titaniferous mag- 

 netite are rare, and in nearly every case form the nucleus of 

 titanite areas, which are apparently their alteration product. 

 Long slender prisms of apatite are very abundant. 



Specimens of the schistose variety vary a good deal. In a 

 specimen given me by Mr. Sears the feldspars are largely in 

 small anhedra, and the structure is microgranitic. Most of them 

 are simple, perthites are not very common, twinning lamellae 

 rare. They have a brecciated structure and sometimes undu- 

 latory extinction, suggesting that the tendency to schistosity is 

 due to pressure. Nepheline is present in considerable amount. 

 Small irregular anhedra of a bright green aegirine-augite are 

 scattered abundantly through the mass. A few large pale fawn- 

 colored augites are seen, always more or less altered to a granu- 

 lar aegirite-augite. Small flakes of greenish-brown biotite and 

 grains of titanite, often highly automorphic, are abundant, horn- 

 blende is almost wanting, and apatite scarce. 



In other specimens the granitic groundmass is on a larger 

 scale, the feldspars tabular and microperthite common, and 

 interstitial nepheline abundant. An olive-green hornblende in 

 beautifully automorphic crystals takes the place of the aegirite- 

 augite, which is absent ; large diopsides are rare, biotite almost 

 wanting, titanite and apatite not abundant, and magnetite 

 extremely scarce. No olivine was found by me in any of the 

 varieties of the normal essexite. 



