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violence to the rules of lithologic nomenclature to call this rock 

 granite. It closely resembles a rock of the Naugus Head 

 series on the Beverly shore ; and it is probably an outlier of 

 that formation. It occurs as an eruptive, cutting the adjoining 

 diorites ; and I have given it the Naugus Head color on the map. 

 Continuing northward, we find the granite of the large area 

 between Beverly and Rockport characteristically coarse, and, as 

 a rule, little hornblendic, especially towards the north-east, 

 where, as already noticed, the hornblende is sometimes replaced 

 by mica. The granite in Essex, Ipswich, Hamilton, and Tops- 

 field, so far as observed, appears to belong here. In the latter 

 town it disintegrates readily, and is known as the "rotten rock. " 

 Coarse, little hornblendic granite occurs in Rowley, along the 

 railroad, north of the station, and at several points in Newbury, 

 north of the river Parker. In both towns it becomes finer- 

 grained towards the west. 



We have traced this type over a large area, and have found 

 it everywhere presenting substantially the same characteristics. 

 Though the limits of local variation in texture and composi- 

 tion are wide, yet to the general view it remains essentially un- 

 changed ; and the observer feels that, from Plymouth to the 

 Merrimac, from Rhode Island to Cape Ann, it must be, in its 

 origin and petrologic relations, one and the same rock. 



2. The fine-grained, little hornblendic granite contains even 

 less hornblende than the typical variety ; and, like that, it is 

 frequently a binary granite, — composed entirely of orthoclase 

 and quartz. This variety not unfrequently appears, when con- 

 taining little or no hornblende, to pass through eurite into petro- 

 silex. I am unable to point to any particular locality as afford- 

 ing incontestable evidence of this transition ; yet indications of 

 such a passage are constantly presented to the observer. He 

 meets on every hand partial proofs ; and, whether studying 

 granite or petrosilex, he is ever finding rocks which are neither, 

 but both, — until the gradation is complete, and the conclusion 

 is forced upon the mind that these rocks must be unequally 

 metamorphosed portions of one and the same original rock. This 



