THE STRATIFIED ROCKS OF ESSEX COUNTY. 45 



clase deeply kaolinized ; both the plagioclase and the or- 

 thoclase having numerous inclusions of quartz and biotite. 

 There are also grains of epidote and fine dust-like ferrite, 

 and muscovite plates arranged parallel to the bedding. 

 Microscopic structure of section of specimen (No. Ill) 

 from John Noyes' Copper Mine, New bury, closely resem- 

 bles the sections from Boxford (Nos. 109, 110) excepting 

 that there is more biotite, that numerous cubes of iron 

 pyrite are scattered through the dust-like ferrite and that 

 microliths are of numerous occurrence. 



In the northern part of the county, occupying nearly the 

 whole of the region known as Ballard Vale, West Ando- 

 ver, South Lawrence, a part of North Andover, Bradford, 

 Haverhill at Aver Village, and passing into New Hamp- 

 shire, is a coarse granitoid gneiss cut by dykes of eruptive 

 hornblendic granite and diorite. In Andover and North 

 Andover the strike of this gneiss is east 40 north, paral- 

 lel to the metamorphic slate, dip 35 southwest. A large 

 area of this gneiss in West Andover and South Lawrence 

 has been opened for quarrying purposes and fine exposures 

 may be seen in a quarry at South Lawrence worked by Mr. 

 Jesse Moulton. The strike at this point is east 20 north, 

 dip 85 south of west. The microscopic structure of sec- 

 tions of this rock is : coarse masses of orthoclase, micro- 

 cliue, quartz, muscovite, garnets cemented together by a 

 thin film of secondary quartz. Numerous inclusions of 

 quartz, biotite and muscovite are seen in the feldspars. 

 I have traced this gneiss by means of numerous outcrops 

 through South Hampton, Hampton and Rye to the Isles of 

 Shoals. At Rye an old quarry offers good facilities for 

 study, and specimens received from Appledore Island are 

 of the same character and show the same microscopic 

 structure in thin section. 



At Folly Point, Lanesville, and also at West Glouces- 



