Abstract: In the Blue Ridge Province of northern Virginia, Maryland, and southern Pennsylvania, Lower Cambrian beds are underlain by a thick sequence of greenstone and interbedded sedimentary rocks known as the Catoctin Formation. An area near Luray, Va., was studied to determine the thickness of the formation, its relationship to overlying and underlying rocks, and the original nature of the lavas from which the Catoctin greenstone was derived. There the Catoctin Formation lies unconformably on granitic rocks. Its basal sedimentary layer ranges from a few inches to 150 feet in thickness and contains pebbles of underlying basement rocks. The erosion surface beneath the Catoctin is irregular, and in several places, hills as much as 1,000 feet high were buried beneath the Catoctin lavas. No important time break is indicated between the deposition of the Catoctin Formation and the overlying Cambrian sediments. The original Catoctin lavas were basaltic and were probably normal plateau basalts. Columnar joints, amygdules, sedimentary dikes, flow breccias, low-dipping primary joints, and other primary structures are well preserved.

From introduction: This study was undertaken as part of the U.S. Geological Survey's (USGS) Reactor Hazards Reduction Program. One of the goals of this program is to contribute to the growing recognition and cataloging of Cenozoic faults in the Atlantic Coastal Plain. Once the faults are recognized and cataloged, the stress field and resulting tectonic framework that produced these faults can be determined. This study defines the stratigraphic and structural relationships of a tectonically anomalous area in the vicinity of Hopewell, Va.