110 BULLETIN OF THE ESSEX INSTITUTE. 



on advice at the time, although I personally felt then that 

 it would have been better to do so. Another correction 

 is an addition to the augite-nepheline-syenite area. The 

 augite-nepheline-syenite area in Gloucester and Rockport 

 has been extended over two miles and remapped on the 

 west side of Cape Pond. This work was greatly assisted 

 by the Gloucester and Rockport street railroad work and 

 the trenches opened by the Rockport water works, when 

 numerous sections of the fresh rock were exposed thus 

 aflbrding good specimens of the rock for investigation. 

 Many specimens from these outcrops have been collected 

 and the data thus at our disposal have been of great help 

 in tracing this rock formation. The trend of the auojite- 

 nepheline-syenite rock from Gloucester to these outcrops 

 in Rockport and to Sandy bay and the Dry Salvages is in 

 the usual northeast direction and unites in this area the 

 augite-nepheline-syenite, the so-called black granite of 

 the Rockport Granite Company's Quarry. Having thus 

 traced the augite-nepheline-syenite in comparatively nar- 

 row area, through the hornblende-biotite-sfranitite rock- 

 mass, it is an indication that the syenite is the younger 

 rock and cuts through thegranitite without these recently 

 seen outcrops; and, with the knowledge at our command 

 when the geological map of Essex County was published, 

 the small detached areas of the augite-syenite in this 

 region seemed to be cut by the granitite, thus making the 

 granitite apparently the younger rock. I have therefore, 

 taken all of the maps remaining on hand at the Essex 

 Institute and have made the necessary corrections to date 

 in color. 



These corrections may not appear important to the un- 

 trained eye ; still they are so to the student and it at least 

 brings the maps on hand correct to our best knowledge to 

 the present time. 



