Portsmouth Basin, Me. and X. H. 153 



Syenite. — The syenite forms an irregular stock-like 

 mass measuring three and one-half by four miles. The 

 field habit of the rock is varied, all gradations being seen 

 from a fine-grained grayish-green quartz-free syenite to 

 a coarsely pegmatitic rock consisting essentially of 

 perthitic feldspar, quartz, and arfvedsonite. The oli- 

 vine, fayalite, occurs rather abundantly in the contact 

 phases ; in some of the central phases, arfvedsonite, 

 riebeckite, orthite, aegerite, and zircon become locally 

 abundant. 



Contacts of this rock against the alkaline granite are 

 rather poor so that age relations cannot be established 

 with certainty. Along the northwestern margin of the 

 syenite this rock appears to dike the alkaline granite. 

 The syenite, usually a quartz syenite (nordmarkite) in 

 composition, is in turn cut by the lenticular masses of 

 rather coarse-grained pegmat.ic quartz syenite, thus indi- 

 cating an additional concentration of volatile components 

 in the later stages of this intrusive. 



Volumetric composition of two phases of the Agamen- 

 ticus complex : 



I II 



Alkaline feldspar 87.90 76.02 



Fayalite 3.76 



Aegerite augite 3.35 2.61 



Quartz 2.43 17.46 



Arfvedsonite 49 3.55 



Biotite 61 



Magnetite 73 .... 



Allanite .19 



Zircon .09 



Totals 99.27 99.92 



I. Border phase of the syenite. 

 II. Typical alkaline granite from Mt. Agamenticus. 



. Berwick Quartz Diorite. — Apparently later than the 

 main biotite granite is the small stock of quartz diorite 

 situated about two miles east of Berwick. The contact 

 phase is essentially a gabbro, but the central mass is a 

 typical quartz diorite. This body may possibly be cor- 

 related with the Cape Xeddick gabbro. 



Other Granitic Bodies. — In addition to the above men- 

 tioned occurrences of granite there are other small bodies 



