476 HENRY S. WASHINGTON 
direction in a broad zone which runs north-northeast from 
Beverly to Ipswich. Interspersed with the granite and surround- 
ing some of the smaller areas is quartz-syenite, which is not met 
with west of the granitic zone, except in two small patches. 
West of the granite area, and forming also a broad zone running 
north-northeast, is the main area of diorite, which curves around 
to the south, forming the Salem area, and is also met with as 
strips and tongues in the granite areas. West and northwest of 
the diorite are found sedimentary and metamorphic rocks, of 
which something will be said later. The ‘small area of foyaitic 
rocks lies near Salem, south of the western parts of the granite 
and quartz-syenite areas. The gabbro is only met with at the 
extreme south, on the small promontory of Nahant with patches 
of metamorphosed Cambrian sedimentaries. To the south near 
Lynn, and north near Newburyport, are areas of rhyolite, a 
small patch of which is also found at Marblehead Neck, south- 
east of Salem. : 
There is then a rather regular arrangement, the acid rocks 
being to the east and the basic diorites surrounding them to 
west and south, lying on the outside next to the nonigneous 
rocks. This is suggestive of the arrangement of the rocks in 
the ordinary type of differentiated laccolith. 
In the ‘next’ place, according to Mr Sears: map and hus 
description of the sedimentary rocks,’ we find that the dips of the 
sedimentaries and metamorphosed rocks, which form the western 
part of the county, are in general to the northwest or north- 
northwest, z. ¢., away from the igneous area. This is also 
suggestive of a laccolithic mass, and the few small areas of sedi- 
mentaries metamorphosed by contact with the igneous rock, 
which are met with here and there through the igneous areas, 
may be considered to be remnants of the original cover. In 
fact, Mr. Sears, himself, indicates the conclusion that the mass is 
an anticlinal laccolith, when he says:? ‘The position of these 
two metamorphosed crystalline sedimentary beds signifies that 
® 
tSEARS: Bull. Essex Inst., Vol. XXII, p. 1, 1890. 
?SEARS: Bull: Essex Inst., Vol. XXIII, p. 15, 1891. 
