THE STRATIFIED ROCKS OF ESSEX COUNTF. 37 



quartz and feldspar grains, numerous flakes of muscovite 

 with detrital angular fragments and pebbles of the quartz, 

 feldspars colored with ferreous oxide, some epidote and 

 chlorite and threads of calcite. 



Continuing on the strike of this shale, there are two out- 

 crops in the northeastern part of Topsfield, one in Line- 

 brook, a parish of Ipswich on Bull Brook, one in Rowley 

 near John Dodge's mill and another near tide water be- 

 tween Ipswich Village and Rowley. The microscopic 

 structure of the sections from specimens in the cabinet of 

 the Peabody Academy of Science from these localities is 

 nearly the same as that of the last two from Topsfield. 

 Other outcrops of these clastic shales are frequent in the 

 northern part of the county. There is on the south bank 

 of the Merrimac near the Artichoke river, a large area of 

 this shale much crumpled and distorted with the strike 

 north and south and dip vertical. Near the point where 

 Indian river empties into the Merrimac the shales are 

 continuous for three hundred yards, and from Bradford 

 across North Andover and South Lawrence, in a south- 

 west course, they can be traced in an almost unbroken line 

 to West Andover. On this strike the shales are bedded 

 between the granite gneisses on the south and the rneta- 

 morphic 'slates on the north. 



At North Satigus, near the corner of Main and Oak 

 streets, is an outcrop of metamorphic slate interstratitied 

 with a quarlzite, and on Main street two hundredyards east 

 of the school house the hornblendic eruptive granite cuts 

 directly across this metamorphic slate and includes lar"ge 

 fragments of it. The strike of these metamorphic slates 

 and quartzites is north 20 E. parallel to that of similar 

 beds at Lynnfield Centre. The microscopic structure of this 

 metamorphic slate is : clastic quartz grains with many fluid 

 inclusions, well-rounded grains of plagioclase, orthoclase 



