Portsmouth Basin, Me. and N. H. 1-tl 



Areal Geology. 



General Statement. — The Portsmouth Basin resembles 

 in many respects the other fragmentary geological basins 

 which have been recognized in the as yet imperfectly 

 known area of the Northern Appalachians. The rocks 

 consist of fine-grained steeply inclined sediments 

 supposed to be of Upper Carboniferous age, of both intru- 

 sive and effusive igneous rocks, and of some thoroughly 

 metamorphosed rocks of doubtful origin and unknown 

 age which have been classified as gneisses and schists. 

 The sediments and the metamorphic rocks have a general 

 strike of X 45° E, but local departures from this general 

 direction are numerous ; the dikes of the region follow 

 a northeasterly trend; and the batholiths are elongated 

 in the same direction. The dip of the stratification of 

 the sediments and of the schistosity of the metamorphics 

 is, on the whole, to the northwest, but frequent departures 

 from this direction indicate, perhaps, local folds and 

 crumplings. The gneisses and schists occur both to the 

 northwest and to the southeast of the sediments of Upper 

 Carboniferous age, and since the highly metamorphosed 

 rocks almost close in on the sediments to the southwest, 

 a basin-like arrangement results. 



Sedimentary Rocks. 



General Statement. — Hitchcock s in his survey made no 

 attempt to separate the rocks of the Portsmouth Basin 

 into groups or formations, as is indicated by the following 

 quotation: "This name (Merrimack Group) was infor- 

 mally applied by my father to the mica schists, slates, and 

 quartzites contained in the Merrimack River, in Massa- 

 chusetts. They skirt the Exeter sienites in New Hamp- 

 shire, lying in troughs in an anticlinal. They probably 

 belong to the earliest Silurian." On purely lithologic 

 grounds it seems possible to separate this "Merrimack 

 group of Hitchcock's into two groups. The first contains 

 three formations which have been called the Gonic schist a , 

 the Berwick gneiss' 3 , and the Rye gneiss ; the second con- 



s Geology of New Hampshire, Concord, Xew Hampshire, p. 27, 1878. 

 a Correlated by Katz, as a part of the Eliot formation but lithologically 

 different. 



b Is the same as the Berwick gneiss of Katz. 

 c Is the Algonkian complex of Katz. 



