THE PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 797 
contain very little, but it is never wholly absent. Black spots 
of augite are abundant and magnetite is seen here and there. 
The microscope reveals the presence of the following min- 
erals: quartz, alkali feldspar, diopside, hornblende, biotite, mag- 
netite, apatite, and titanite. Quartz is not very abundant and is 
the last product of crystallization, occupying the interstices 
between the other minerals. It is undoubtedly primary, but the 
extinction is very often undulatory. The feldspars are mainly 
microperthitic intergrowths of orthoclase and albite, and resem- 
ble closely those of the granite. Microcline is rare. The feldspars 
are highly irregular as a rule, though some crystal outlines are 
seen against interstitial quartz. The boundaries between the 
adjacent crystals are generally zigzag or brecciated, indicating 
that the mass has been subjected to stresses. Some small albites 
show beautifully fine and clear twinning lamelle. As they occur 
in such brecciated areas they may be supposed to be secondary. 
The feldspars very commonly show signs of alteration which is 
evidenced by a cloudy appearance, or when the crystal substance 
is clear by the cleavage lines and cracks being filled with a green- 
ish decomposition product, the exact nature of which could not 
be determined. 
The pyroxene occurs in scattered crystals of irregular out- 
line. It is nearly colorless or a pale greenish-gray, without 
pleochronism but with high extinction angles. It is not infre- 
quently uralitized on the edges, and carries inclusions of magne- 
tite, apatite, and titanite. Primary hornblende of deep green or 
brownish colors is common in some specimens, notably in those 
from Poorhouse Hill, Beverly, and Cape Pond, Rockport. This 
is also intergrown with the pyroxene in parallel positions. Bio- 
tite is extremely rare or entirely wanting in these rocks, and 
when present is almost certainly secondary. Magnetite and 
apatite, occasionally in very long needles, are more common 
than in the granite. Zircon is present but is less abundant. 
Colorless titanite is quite common, usually in almost square sec- 
tions with oblique extinctions. No nepheline was to be found in 
any of my sections, although Sears notes its presence. Its occur- 
