- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Seven mappable lithologic units are recognized: a southern gneiss terrane of plagioclase-quartz gneiss, augen gneiss, amphibolite, and a quartz-diorite body; and a northern granitic terrane of intergradational, scattered bodies of quartz monzonite, quartz diorite, and agmatite. Regional synformal structures with steep dips are defined by foliation in both terranes; with local exceptions, contacts between rock units are broadly parallel to regional strike of foliation -- E-W, E-NW, and NE-SW. Many rock units are transgressed by limited shear zones and marked by retrograde metamorphism as well as faults. The northern granitic complex evolved essentially contemporaneously with the southern gneiss during a period of metamorphism and metasomatism; late mobility of potash at the north end converted the gneiss there to granitic rocks. The isolated Bald Mtn. area may represent the center of such metasomatic activity.