The Mt. Washington quadrangle contains the highest peaks in the northern part of the Appalachian Highlands. This paper presents a brief summary of the geology to accompany a colored geological map that has just been printed. The stratified rocks belong to three formations, the Ordovician (?) Albee formation, the Ordovician (?) Ammonoosuc volcanics, and the Devonian Littleton formation. All these rocks have undergone high-grade metamorphism, and such minerals as andalusite, sillimanite, staurolite, garnet, tourmaline, actinolite, and diopside are present. The intrusive rocks belong to four magma series, ranging in age from Late Ordovician (?) to Mississippian (?).
The structure of the whole quadrangle is dominated by a northeasterly trending dome, the center of which is occupied by the intrusive Oliverian magma series. The metamorphosed sedimentary and volcanic rocks on the flanks of this dome are thrown into countless folds, ranging from minor folds seen in single outcrops to larger folds hundreds and thousands of feet in wave length and amplitude. The folding is probably Acadian (middle to late Devonian). The intrusive rocks show a variety of structural forms. The Oliverian magma series apparently consists of a series of concordant lenses. The White Mountain magma series occurs in ring-dikes, stocks, and volcanic vents.