BRITTLE STRUCTURES AND THE GRANTHAM FAULT WITHIN THE SOUTHERN HALF OF THE 7.5-MINUTE GRANTHAM QUADRANGLE, NEW HAMPSHIRE
The Grantham Fault is characterized by kink folding and silicified zones of almost pure quartz that are chaotic in orientation. There are small areas of the silicified zones that are brecciated. The portion of the quadrangle east of the Grantham Fault is Devonian Bethlehem Gneiss, which has a generally subhorizontal foliation with 48% of these foliations displaying parting displacement. Parting fractures are observed at almost every outcrop, but there are also fractures that are perpendicular to foliation commonly influencing the topography. The outcrops closer to the fault are more variable in fracture orientation. Many of these fractures are perpendicular to foliation. Steeply dipping fractures that strike approximately 185 degrees are prevalent near the Grantham Fault. West of the Grantham Fault there is a diversity rock types, represented by the Ordovician Ammonoosuc Formation, Silurian Clough and Fitch Formations, Devonian Littleton Formation, and the Croydon Dome rocks. These formations have a greater number of fractures that are perpendicular to foliation, as well as symmetric fractures that have spacing of approximately 1 m. A much lower percentage, approximately 20 percent, of these foliations have parting fractures.