Portsmouth Basin, Me. and N. H. 151 



quartz cliorite, quartz biotite diorite ; and a central phase 

 of granodiorite, granite, and granite aplite. 



Volumetric composition of two phases of the Durham 

 quartz diorite : 



I II 



Plagioelase (Ab 3 An 7 — Ab 6 An 4 ) 63.15 



Mieroperthite to oligoclase 56.06 



Quartz 10.03 17.10 



Biotite 16.21 15.92 



Pvroxeue 8.91 .... 



Amphibole 1.68 10.10 



Apatite .01 



Totals 99.98 99.19 



I. Quartz diorite 300 feet from the contact. 

 II. Granite from the central portion. 



Other bodies related to the quarts diorite. — Two other 

 bodies within the area resemble the Durham batholith, 

 not only in composition, but also in a similar gradation 

 from basic margins to a more acidic central phase. One 

 of these, a small stock, occurs about two miles east of 

 North Berwick ; the other, also stock-like in habit, occurs 

 at the intersection of the North. Hampton, Exeter and 

 Newington boundaries. 



Cape Xeddiek Gabbro. — The Cape Xeddick gabbro 

 forms a small oval stock measuring about one-half by 

 three-fourths of a mile. It is well exposed and shows 

 particularly fine contact phenomena as well as variations 

 in composition. This stock shows four phases: (a) the 

 contact phase, a medium to fine-grained rock rich in 

 olivine, myrmekite, and apatite, and contains abundant 

 inclusions of the invaded quartzites ; (b) a dark coarse- 

 grained phase (phenocrysts may show a diameter up to 

 2 cm.) having about equal amounts of the light and 

 dark minerals which are poikilitically intergrown and 

 characterized furthermore by a vertical banding parallel 

 to the contacts; (c) a very dark, almost black phase, 

 medium to coarse in grain, containing olivine embedded 

 in large poikilitic crystals of hornblende, biotite, and 

 titaniferous pyroxene; and (d) a light colored central 

 phase composed largely of plagioelase feldspar accom- 

 panied by small amounts of quartz and orthoclase. 



