THE STRATIFIED ROCKS OF ESSEX COUNTY. 43 



secondary quartz, some plagioclase deeply kaolinized, 

 ground-mass of kaolinite, epidote and magnetite and some 

 zoisite in the plane of the bedding. Specimen (fibrolite 

 gneiss) collected at Marble Ridge, south of the railroad 

 station : quartz, plagioclase and orthoclase feldspars in 

 grains, large flakes of muscovite, biotite, and acicular crys- 

 tals of fibrolite, in aggregates, scattered through all the 

 minerals ; the plagioclase has numerous inclusions of quartz 

 and the biotite inclusions of zircons and garnets which 

 show fine pleochroic halos. In the ground-mass are patches 

 that strongly resemble corderite, but so much altered that 

 determination is difficult. In hand specimens this rock is 

 nearly identical to the genuine corderite gneiss. 



Hornblende epidote gneiss from Crooked pond, East Box- 

 ford ; section across the bedding, microscopic structure : 

 green hornblende, twinned feldspar with numerous inclu- 

 sions of quartz grains, patches of quartz in which there 

 are numerous fluid inclusions, large patches of zoisite, bi- 

 otite and magnetite, numerous areas of chlorite and some 

 epidote. Section parallel to the bedding shows the zo- 

 isite surrounding hornblende crystals and the hornblende 

 in turn surrounding grains of magnetite, all lying in one 

 plane across the section dependent upon one plane of pres- 

 sure. Titanic iron surrounded with leucoxene is abundant 

 in this section. Specimen from east of Chadvvick's pond : 

 quartz grains, apparently detrital, with numerous fluid in- 

 clusions, much biotite, some plagioclase with inclusions of 

 quartz, some chlorite and magnetite. This may be termed 

 a biotite schist. Metamorphic hornblende epidote gneiss 

 from Smith Mine, Newbury. Microscopic structure of 

 section across the bedding : green hornblende with numer- 

 ous inclusions of plagioclase and magnetite, much biotite, 

 some muscovite, grains of quartz showing enlargement by 

 the addition of secondary quartz, orthoclase much decom- 



