38 THE STRATIFIED ROCKS OF ESSEX COUNTY. 
almost entirely decomposed, biotite, some muscovite, and 
magnetite, gromid-mass, a ferruginous earthy kaolin with 
some fibrous chlorite and a few grains of epidote. 
The qnartzite from the same phice in thin section shows : 
quartz grains with numerous fluid inclusions, feldspars much 
kaolinized and containing numerous inclusions of a})atite, 
tourmaline and epidote, while patches of chlorite are often 
seen in the line of the bedding ; the whole rock mass is 
thoroughly saturated with a ferruginous limonite giving it 
a dirty yellowish cohn". The microscopic structure of the 
quartzite from Lynnfield Centre is ; quartz grains contain- 
ing numerous fluid inclusions and incipient cracks, also 
crushed and broken grains produced by pressure in the rock- 
mass during metamorphism, nmch secondary quartz which, 
with the polariscope, gives the usual w^avy extinctions, some 
grains of secondary glassy plagioclase, perfectly fresh grains 
of microcline, orthoclase kaolinized and much decomposed, 
with numerous inclusions of zircons and apatite crystals, 
some chlorite and a little biotite. This outcrop is exposed 
for a distance of one hundred yards and is in some places 
finely schistose and laminated, while in others it is massive ; 
the strike is north 20° east, dip 50° west. 
Nearly all of the bed rock of West Newbury, Groveland, 
Haverhill, Bradford, Lawrence and Methuen is composed 
of metamorphic slate. The microscopic structure of a spec- 
imen of this rock from Ward's Hill, Bradford, section cut 
across the bedding, is largely of detrital grains and an- 
gular fragments of quartz, many of which are crushed and 
broken, orthoclase grains nearly all kaolinized and earthy, 
biotite mica abundant in the pltmcs of the schistosity, some 
original muscovite, microscopic zircons, rutile and titanic 
iron. A section i)arallel to the bedding shows large masses 
of chlorite developed as a product of decomposition of the 
biotite and inclusions of apatite crystals are abundant. 
