THE STRATIFIED ROCKS OF ESSEX COUNTY. 35 



an abundance of magnetite and some limonite. The dis- 

 integration of this rock produces the magnetite and garnet 

 sand of the region. The mica schist of Nangus Head, 

 Marblehead, and Woodbury's Point, Beverly, probably be- 

 long to this metamorphic slate although the metamorphism 

 is more complete ; for, in these last named outcrops, the 

 schist is not only cut by the granite but it is also cut by 

 the diorite, eleeolite zircon syenite, felsite and diabase 

 dykes, thus making the metamorphism of the rock-mass 

 most intricate ; indeed, as pointed out by Dr. M. E. Wads- 

 worth, the elaeolite zircon syenite has been injected in 

 large sheets into these schists, in the planes of the schist- 

 osity and jointings of this rock, to such an extent that in 

 some places it is puzzling to decide which is syenite and 

 which is mica schist. 



Microscopical examination shows this schist to be com- 

 posed of a few grains of clastic quartz sand, much secon- 

 dary quartz, secondary glassy feldspars, some muscovite, 

 an abundance of biotite which is probably secondary, a few 

 grains of epidote, apatite as inclusions in the ground-mass 

 which is feebly polarizing earthy kaolin, much magnetite, 

 red garnets and micro : zircons. 



In Middleton, half a mile southeast of the village, near 

 the house of Mr. J. U. Parker, is a well preserved clastic 

 shale approaching a sandstone. This outcrop shows a strike 

 nearly northeast to southwest with the dip 50 north of 

 west ; it is again seen in an outcrop in the rear or west side 

 of the barn of Mr. Francis Peabody near the Ipswich river 

 on the north side of the village. The microscopic structure 

 of this shale is : angular and rounded grains of quartz which 

 show embryonic cracks and much crushing and in some 

 grains a secondary enlargement, plagioclase twinned feld- 

 spars broken and crushed, some of which are in well-round- 

 ed grains ; ground-mass an earthy kaolin with plates of bi- 



