124 GEOLOGICAL AND MINERALOGICAL NOTES. 



IN CONCLUSION. 



The geological age of the granitic rocks of which this 

 paper treats is undoubtedly post Cambrian as large and 

 small fragments of the metamorphosed Cambrian sedi- 

 ments are often seen to be included in them. On Poor 

 house hill, in Beverly, and Conomo Point, in Essex, ex- 

 amples of these included Cambrian rocks are met with on 

 all sides. In regard to the relative age of these rocks as 

 compared with the hornblende-granitite, the granitite is 

 the younger rock ; for the massive forms of the augite- 

 syenite are not seen cutting the granitite but usually sur- 

 round it, thus forcing the conclusion that the granitites 

 have burst up through the augite-syenites. The micro- 

 syenite and tinguaite dyke rocks are more recent for they 

 often cut both the granitite and the massive augite-syenite. 

 Dr. M. E. Wadsworth in his paper on the presence of 

 syenite in Essex County, Mass. (Geological Magazine, 

 Decade 3, Vol. 2, No. 5, p. 207), says, "The preponder- 

 ance of evidence is that the granite is the younger rock 

 unless it is contemporaneous with the syenite." In the 

 9th Annual Report of the U. S. Geological Survey (Ge- 

 ology of Cape Ann, Mass., by Prof. N. S. Shaler), the 

 rocks of this area were mapped and classified as hornblende 

 granitite, with the exception of a small area in Squam 

 river and vicinity which was mapped as diorite. This so- 

 called diorite, as is shown in the microscopical analyses 

 of thin sections from all parts of the area described, is 

 composed of augite-syenite minerals and the few sections 

 that were wanting in some of these minerals would be 

 nearer a fine grained hornblende-granitite than a diorite. 

 The city of Gloucester is built almost entirely upon this 

 augite-syenite. It was stated in the text of the Geologi- 

 cal Report that the ledge at Magnolia and the islands on 

 the coast were syenitic in character, but on the map of the 



