REPORT ON THE GEOLOGY OF ESSEX CO., MASS. 121 



Geological and Mineralogical Notes : No. 6. On the 

 Occurrence of Augite and Nepheline-Syenites in Essex 

 County. (Bulletin Essex Institute, Vol. xxv, 1893). 



A paper (Bulletin Museum Comp. Zoology, Harvard 

 University, Vol. xvi, No. 9) : Keratophyre from Mar- 

 blebead Neck. 



Other papers are in course of preparation on the quartz- 

 augite-diorite ; the granitic arkoses of the northern part 

 of Essex County and on the conglomerates and interstrat- 

 ified red slate, limestone and quartzite beds of Middleton, 

 Topsfield and Boxford. 



In studyiug the rocks for the preparation of these papers 

 over onethousand thin sectionsand slides have been made 

 for microscopical and microchemical tests in determining 

 the minerals composing them. The determinations have 

 all been made at the petrographical laboratory of Harvard 

 University with the kind assistance of Dr. J. E. Wulff. 



The Classification here employed largely follows that of 

 Professor Rosenbusch of Heidelberg University, as given 

 in " Notes to Accompany a Tabulation of the Igneous Rocks 

 based upon the System of Prof. H. Rosenbusch," by Frank 

 D. Adams, Lecturer McGill University; published in 

 Canadian Record of Science, Dec, 1891. 



PLUTONIC ROCKS : HYPIDIOMORPHIC GRANULÄR 

 STRUCTURE. 



No. 1. Hornblendic-Granitite. 



This name was given to the granitic rocks of Cape 

 Ann by Dr. M. E. Wadsworth and is equivalent to 

 the biotite-granitite of Professor Rosenbusch. Under 

 the general type there are several varieties, either coarse 

 or fine grained, and containing iittle or much biotite. 

 The Peabody and Lynnfield granitites contain Iittle bio- 

 tite, while in the Gloucester and Rockport granitites there 



ESSEX INST. BULLETIN, VOL. XXVI 16 



