Abstract Black shales are integral parts of most foreland-basin deposits and, because they typically reflect maximum basin subsidence, their distributions serve as proxies for the extent of foreland-basin development. In the United States Appalachian area, the distribution of Middle–Upper Ordovician black shales suggests that the Taconian Orogeny proceeded from south to north along the eastern Laurentian margin and that Taconian tectophases were mediated by convergence at continental promontories. In the Late Ordovician Taconic tectophase, changes in the distribution of the Martinsburg and Utica black shales support a reversal of subduction polarity that effected the reactivation of basement structures and basin migration sufficient to yoke the Appalachian foreland basin with adjacent intracratonic basins. Shale distribution suggests that early Chatfieldian (late Sandbian–early Katian), east-verging subduction early in the tectophase generated a cratonic extensional regime with a narrow foreland basin that developed along reactivated Iapetan basement structures. Abruptly, in late Chatfieldian–early Edenian (early Katian) time, westwards migration of basinal Utica black shales and an underlying unconformity suggests change to a compressional regime and westwards subduction vergence. The coincidence of changes in basin shape and migration with the shifts in subduction polarity suggests a causal relationship.

Abstract Many of the parks within the National Park System owe their uniqueness to their geologic framework. Their scenery is the result of diverse natural processes acting upon a variety of rocks that were deposited in varied environments in the geologic past. The Delaware Water Gap National Recreation Area (DEWA) contains a rich geologic and cultural history within its 68,714 acre boundary. Following the border between New Jersey and Pennsylvania, the Delaware River has cut a magnificent gorge through Kit-tantinny Mountain, the Delaware Water Gap, to which all other gaps in the Appalachian Mountains have been compared. Proximity to many institutions of learning in this densely populated area of the northeastern United States (Fig. 1 ) makes DEWA an ideal locality to study the geology of this part of the Appalachian Mountains. This one-day field trip comprises two stops within the gap itself and will include discussion on stratigraphy, structure, geomorphology, and glacial geology. The first stop will be at the bottom of the gap in Pennsylvania to look at the magnificent exposures in the cleft on the New Jersey side. This will be followed by a traverse to the top of Mount Tammany along a popular trail, where we will compare the geology across the river in Pennsylvania. Much of the information presented in this guidebook is summarized from Epstein (2001a , 2001b , 2001c ) and Epstein and Lyttle (2001) .

Soil-gas radon and ground radioactivity surveys across a portion of the Great Valley of West Virginia indicate that residuum and soils formed above some carbonate rocks have sufficient levels of radon gas to cause high indoor radon values. Data indicate no correlation of soil-gas radon concentration with faults, cleavage, joints, or calcite veins. Instead, soil-gas radon distribution appears to be controlled by the solution of carbonate bedrock and the subsequent development of thick, red, clay-rich residuum, which may contain as much as 4 times the concentration of radium, 10 times the concentration of uranium, and 5 times the concentration of thorium as the underlying bedrock. Such residuum and associated soil develops over some parts of the Elbrook, Conococheague, and Beekmantown Formations, and can have concentrations of radon in soil-gas exceeding 4,000 pCi/L. In areas of the Great Valley underlain by siltstone, fine-grained sandstone, and shale of the Martinsburg Formation, soil-gas radon values can exceed 4,000 pCi/L. In these areas, bedrock alone appears to have sufficient thorium, radium and uranium concentrations to generate the soil-gas radon measured. Previous work by others and our own preliminary evaluations indicate that soil-gas radon levels are high enough to cause indoor air in homes to exceed 4 pCi/L, the U.S. Environmental Protection Agency’s (EPA) action level for radon. Aeroradiometric maps and National Uranium Resource Evaluation (NURE) Program data do indicate anomalously high radioactivity in some areas where radon soil-gas concentrations were high. These data, used with available geologic maps, soil maps, and maps showing thickness of residuum, are useful in predicting areas of radon soil-gas hazards.