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proverbially rock-bound, the Porphyry presenting a perpen- 

 dicular bristling front, while the Greenstone and Syenite 

 piled in massic irregularity along an uneven coast, meets the 

 waves of old ocean with grand sublimity that their mighti- 

 est efforts cannot surpass. 



Below the tide line, the surface of the Syenite and Green- 

 stone is of a very dark' iron-brown color, while above when 

 bare of lichens a lighter brown prevails, indicating the small 

 percentage of iron present in the hornblende. The surface of 

 these formations crossed and recrossedby thousands of veins 

 of various colors, present a striking aspect. President 

 Hitchcock points to a ledge on the shore just at the left of 

 the entrance to Beverly bridge, as an illustration of numer- 

 ous epochs of irruption. This ledge presents the same as- 

 pect with nine-tenths of the surface rock of Marblehead. I 

 hesitate much before differing from so learned and expe- 

 rienced an authority, but from examination of the surface as 

 it exists on a far greater scale in this town, and a hasty exam- 

 ination of tlie ledge the Professor alludes to, I am pursuaded 

 that his inference needs to be greatly qualified, most of 

 the veins, though apparently crossing each other, being veins 

 of segregation rather than veins of injection. 



Much of the surface of our ledges, suggest the appearance 

 of the scum, which rises to the surface of a boiling kettle, 

 whose contents are impure ; should this scum be petrified, 

 while in act of boiling, it would present for the most part the 

 appearance on a small scale that many of our ledges present, 

 or a larger, modified by the elective affinity included in the 

 theory of segregation. Examples of this abound ; a fine il- 

 lustration on a small scale may be found on the surface of 

 the ledge exposed near by the chapel of the Congregational 

 Society in Pearl street. 



On the northern portion of Naugus Head, bordering the 

 water, may be found very fair specimens of Gneiss, the 

 mineral constituents of the Syenite rock there taking this 

 mechanical structure. Along the coast line of the tow^i, 

 but especially on the ocean side of the Neck, a number of 

 dikes have been excavated from twenty to one hundred and 

 twenty-five feet by the action of the waves. On the Neck 

 these Purgatories are in some instances not far from forty 

 feet in perpendicular depth, and the hollow, cavernous sound 

 of the waves rushino- throudi them in our north-east storms 



