Portsmouth Basin, Me. and N. H. U9 



The New England province seems to have been affected 

 by two periods 14 of batholithic intrusion. The first is 

 usually dated as Devonian ( I) and is characterized by 

 granites, granodiorites, and quartz diorites ; the second, 

 or Carboniferous, is characterized by alkaline granites 

 of which the Quincy granite is the typical example. It 

 is probable that the subjacent rocks of the Portsmouth 

 Basin fall into these two groups. In (1) may be placed 

 the Rochester granite; in (2), the Durham, Hampton, 

 Agamenticus, Cape Xeddick, and York Harbor occur- 

 rences. The granite at Brave Boat Harbor is much more 

 sheared than are the other nearby intrusives. It is 

 doubtfully classified as a Carboniferous intrusive. 



Rochester Biotite-Granite. — This body has no unusual 

 features of mineralogical composition. Outcrops are 

 not numerous, the best exposures occurring in a few small 

 quarries. The rock cuts the Gonic schist and may be a 

 pre-Carboniferous intrusive. Pegmatite veins cut the 

 granite and as a rule carry quartz, perthitic feldspar, 

 and muscovite. 



Durham Quartz-Bio rite. — The Durham quartz diorite 

 batholith is an elongated body that extends from two 

 miles southwest of Exeter, X. H., to within one fourth 

 mile of Eollingsford, X. H. It occupies about one third 

 of the Dover quadrangle, has an extreme length of twenty 

 miles, and a maximum width of four and one half miles. 

 Outcrops showing the crosscutting relationships of the 

 body are abundant and the boundaries as shoAvn on the 

 map will need but slight revision. The elongation 

 corresponds to the dominant strike of the invaded sedi- 

 ments. In places inclusions of the Kittery formation 

 occur in various stages of assimilation. 



Although the composition has been indicated as quartz 

 diorite this term merely covers the dominant phase. A 

 distinct gradation from a basic margin to an acidic 

 interior is one of the features of this body. In a section 

 taken across the batholith in a southeasterly direction 

 through the town of Durham, the following variations 

 in composition have been noted: a marginal phase of 

 gabbro, quartz norite, quartz gabbro, quartz augite 

 gabbro ; an intermediate phase of quartz augite diorite, 



14 B. K. Emerson, Geology of Massachusetts and Ehode Island, U. S. Geol. 

 Survey, Bull. 597, p. 172, 1917. 



