of the, Southern part of Essex County. 79 



ARGILLACEOUS SLATE, 



Occurs at the south east extremity of the promontory of Na- 

 hant, associated with flinty slate and argillaceous limestone. Its 

 color is black, ash color, and occasionally striped with green and 

 gray. 



SlENITE. 



An extensive bed of sienite extends in a north east and south- 

 west direction across the south part of Danvers, the south part 

 of Lynnfield, the north part of Lynn, and the north part of 

 Saugus to the town of Chelsea, This range is bounded by Tap- 

 ley's brook on the south east, and by Proctor's brook on the 

 north ; and is from one to three miles in width, forming in many 

 places, high hills of solid rock, and craggy cliffs. Bowlders of 

 sienite from this locality are easily distinguished from those orig- 

 inating from any other. No bowlders of this sienite are to be 

 found to the north of Proctor's Brook, the northern boundary of 

 the bed. In Danvers it is extensively quarried and wrought into 

 mill stones, and into all those architectural articles for which 

 granite is useful. It yields a considerable income to the citizens 

 of Danvers, and has become very celebrated in makirig mill 

 stones of a very superior quality. 



Another range of sienite, but of different quality, extends from 

 Flax pond in Lynn, to the ocean at Swampscut, (also in Lynn.) 

 This sienite is traversed by numerous trap veins, the feldspar is 

 of a red color, and the proportion of hornblende much less than 

 in the Danvers sienite. This variety of sienite extends on the 

 sea coast from King's beach, Lynn, to the line of Marblehead. 



A bed of sienite occurs at Beverly, extending in a north east 

 direction from the north end of Beverly bridge, towards the town 

 of Essex. This bed is but a few rods in width ; greenstone trap 

 prevailing on both sides of the road, leading from Beverly to 

 Gloucester, on the south east ; also on the west side of the most 

 eastern branch of the North River, on the north west. This 

 Sienite is also traversed by numerous dykes or veins of trap, 

 which have been injected into it ; some of which are several feet 

 in thickness. In excavating for the Eastern Rail Road, sixty or 

 eighty rods north of Beverly Bridge, these trap dykes are ex- 

 posed to the depth of twenty or thirty feet ; several of which are 



