of the Southern part of Essex County. 83 



Compact feldspar porphyry passing into greenstone porphyry 

 occurs at Nahant, and about 80 rods south of the Dye Factory, 

 Lynn. 



SILICIOUS BRECCIA AND BRECCIATED PORPHYRY. 



An interruption exists in the porphyry range, before described, 

 by a bed of breccia, which extends quite across it, on the east 

 side of Saugus river. This bed is about half a mile in width from 

 its eastern boundary to the river on the west, and not far from 

 one mile in extent from the sienite on the north, to tide water on 

 the south. 



It has the appearance of being thrown up, in great confusion, 

 forming precipitous cliffs and narrow ravines. A considerable 

 portion of this formation is a conglomerate rock of the grey- 

 wacke series. 



The celebrated Pirate's Glen, is situated in this region. This 

 bed of Breccia embraces also, Willis' Hill, (or Tower Hill,) on 

 which is situated the Lynn Alms House. An eminence on the 

 west side of Saugus river, about half a mile north west of 

 Childs' Mills, has its southern portion made up of porphyry, and 

 the northern of the same species of breccia, which appears to be 

 composed of fragments of porphyry, compact feldspar, horn- 

 stone, jasper, serpentine; &c. The greatest part appears to be 

 brecciated porphyry, but large portions of it are composed of 

 fragments of the other rocks, but quite destitute of fragments of 

 porphyry, forming a pure silicious breccia. Specimens of this 

 variety can be obtained, that are very beautiful. 



Brecciated porphyry occurs also at Red Rock, Lynn. And 

 it is a fact worthy of remark, that distinct and isolated fragments 

 of compact feldspar, exist in nearly all the porphyry throughout 

 the whole range ; but in some places they abound much more 

 than in others. 



A few bowlders and masses are occasionally found, thrown 

 upon the eastern shore of Nahant, 



