152 GEOLOGICAL AND 



neck, when it is considered that the surrounding rock 

 mass is also diorite, proves conclusively that the sections 

 are made from rocks of the same character. 



In Collins cove, Salem neck, there is an outcrop of 

 the pegmatitic vein diorite-gabbro, varying from exceed- 

 ingly coarse to very fine-grained forms, differing so much 

 in portions of the same mass as to make three distinct 

 types. In the first form the main mass is composed of 

 large bluish white feldspar with a few grains of horn- 

 blende and magnetite ; second, the hornblende is in coarse 

 irregular crystals with large masses of magnetite with the 

 feldspar scattered through it in small grains, and in the 

 third form, the feldspars, hornblende and magnetite are 

 about equal in amount, giving the rock at this point the 

 appearance of a hornblende-syenite. The eleeolite-zircon- 

 syenite cuts this gabbro-diorite at several places, small 

 fragments of the gabbro being seen in it. Numerous thin 

 sections that I have cut of each of these forms and studied 

 with the polarizing microscope give about the same gen- 

 eral conclusions. 



Microscopic structure, No. 1. Orthoclase with fine 

 zonal structure, some plagioclase with very coarse twin- 

 ning, a little hornblende with inclusions of augite, much 

 biotite, with zircons that show pleochroic hallows, much 

 magnetite and a few apatite crystals scattered through the 

 orthoclase. 



No. 2. Large masses of brown hornblende, some augite, 

 much biotite and magnetite, some plagioclase, a little ortho- 

 clase and apatite and zircons as inclusions in the biotite. 



No. 3. Orthoclase somewhat kaolinized, a little plagio- 

 clase, hornblende, augite and biotite. The augite is very 

 fresh and numerous good basal sections are seen in the 

 field, much magnetite, some micro-zircons, garnets and 

 apatite inclusions in the biotite. 



