Cross-strike structural discontinuities (CSD's) are broad, diffuse, transverse zones of structural disruption in the Appalachian and other overthrust belts. At Parsons and Petersburg, eastern West Virginia, CSD's are 8 to 10 km wide. Folds of various scales, longitudinal faults, and unmodeled gravity anomalies terminate or change style across or within the two CSD's. Both CSD's are visible on Landsat images. Wherever tested, CSD's contain larger or more abundant joints, normal faults, or both, than do surrounding areas. Mapping usually reveals little displacement across transverse faults that parallel or lie in some CSD's. The CSD's appear to have divided the detached sedimentary prism into quasi-independent structural blocks. Median values of sizes and spacings of the Pa sons, Petersburg, and nine other Appalachian CSD's suggest that each CSD contains about 980 cu km of intensely fractured rock, and that CSD's constitute about 14% of the detached sedimentary rocks. CSD's and their extensions into the foreland can be loci of exploration in gas-producing fractured Devonian clastic rocks of the Appalachian basin. Many short air photo lineaments are surface expressions of fractures or fracture zones. Wells should be sited at intersections of short air photo lineaments in the CSD's.