THE PETROGRAPAICAL PROVINCE OF ESSEX COUNTY 789 
tions will be followed by a general discussion of the results and 
a comparison of this region with others of similar character. 
Granite. —The rocks which belong in this class and which 
are the granitites of Rosenbusch, have been described by Wads- 
worth,’ Shaler? and Sears. They are very abundant in the 
region, covering large areas at Rockport, Gloucester, Manchester, 
Beverly, Essex and elsewhere, having a general northeast-south- 
west trend. 
The specimens in my possession from these localities are all 
hornblende-granites containing more or less biotite. The struc- 
ture is in general typically granitic, a porphyritic development 
of the feldspar being rare. They are quite coarse-grained, the 
texture being fairly uniform in the various specimens. Fine- 
grained forms are less abundant and occur on the borders, as 
will be described later. In color they are usually light mottled 
gray (Rockport, west Gloucester, Manchester), but often yellow- 
ish (Bay View, Eastern Point), or pink (Wolf Hill, Marblehead 
Neck), these last two being due to incipient decomposition. 
The granite of Bass Rock is darker and greenish, forming 
apparently a transition to the augite-quartz-syenite. 
The quartz is often dark and smoky. The feldspars are of 
the usual light shades, with good cleavage, being salmon-colored 
only in the specimens from Wolf Hill. Hornblende and biotite 
are scattered not very abundantly through the mass in black 
irregular spots. These are the principal minerals seen with the 
naked eye, but at the quarries of Rockport and elsewhere a 
large number of accessories have been found, including danalite, 
fayalite, epidote, zircon, magnetite, apatite, fluorite, and others. 
In the area about Rockport pegmatitic veins are not uncom- 
mon, made up of coarsely crystalline feldspar and quartz, the 
latter being occasionally amethystine. The granite, especially 
of Cape Ann, is largely split by joint planes, and also shows a 
strong tendency toward rifting. This has been investigated 
™WADSWORTH, Proc. Bost. Soc. Nat. Hist. Vol. XIX, p. 311, 1878 
2SHALER, oth Ann. Rep. U.S. G. Sury., p. 605, 1889. 
3 SEARS, Bull. Essex Inst., Vol. XX VI, 1894. 
