112 GEOLOGICAL AND MINERALOGICAL NOTES. 



syenite of a reddish and grayish color, which in its macro- 

 scopic characters appears to be identical with that from 

 Plauen'schen Grund, Saxony. The syenite in places con- 

 tains much biotite, and also near West Manchester, quartz 

 grains (segregations?). This syenite is often cut by 

 dykes of a fine grained grayish syenite, which hold the 

 same relation to the syenite proper as the micro-granite 

 dykes do to the granite of the region, and hence, for con- 

 venience of description, the rock of the syenite dykes may 

 be styled micro-syenite. 



A careful study of the rocks of Cape Ann made during 

 the past three years has led to certain conclusions, which 

 are presented in the following pages, together with their 

 macroscopical, microscopical and micro-chemical analyses 

 and the extent of the principal outcrops and the general 

 trend of the whole rock-mass." 



I. DESCRIPTION OF THE ROCK-MASS AT THE VARIOUS 

 OUTCROPS. 



This rock is distinctly plutonic in the coarse massive 

 granitic areas, while in the finer granitic forms it has all 

 the characters of eruptive flows when viewed on the sur- 

 face of the outcrops, but an examination of sections in 

 some of the deserted quarries shows that these flows were 

 due to local variations of the plutonic magma. Probably 

 this is the micro-syenite of Dr. Wadsworth. There are 

 dyke forms, which are intrusive in the hornblende-grani- 

 tite of the region. The syenite rock varies in color from 

 reddish and bluish to all shades of gray and light green > 

 as seen in fresh specimens taken beneath the surface, while 

 on the surface it is weathered to a dull reddish gray. In 

 all cases the rock mass in fresh unaltered specimens con- 

 sists of a compact tough aggregate of well crystallized 

 minerals in which long porphyritic feldspar crystals are 



