INTRODUCTION

The Central Applachian Global Geoscience Transect spans one of the oldest and most intensly studied orogenic belts in the world. The area was included in the geologic map by Maclure [1809], which captured the essential characteristics of Appalachian geology, including the length and width of the orogen, the persistence of individual features for large distances along strike, and the gross stratigraphy. Here, too, the concept of the geosyncline was developed in the writings of Hall [1859] and Dana [1873]. Geosynclinal theory was never adequate to explain orogenic processes, but even today geosynclinal terminology is commonly mixed with newer terms from plate tectonics to describe the sedimentary rocks of the region. Hammer and Heck [1941] made an early attempt to resolve the deep structure of the foreland fold-and-thrust belt using exploration gravimetry, but were unsuccessful because they did not understand the thin-skinned nature of the structural deformation. Rodgers' description of thin-skinned [Rodgers, 1949] or no-basement [Rodgers, 1953] tectonics was based in part on his work in the Appalachian foreland fold-and-thrust belt. Crustal scale seismic refraction studies [James et al., 1968] provided early information about deep crustal structure and topography on the Mohorovicic discontinuity (crust-mantle boundary) beneath the eastern side of the orogen. The Central Applachian Transect corridor is anchored on both ends by on-shore deep crustal seismic reflection profiles, including the COCORP Ohio lines [Pratt et al., 1989] to the northwest and the USGS I-64 [Harris et al., 1982], and off-shore by the Edge 801-803 lines [Sheridan et al., 1993; Holbrook et al., 1994]. Due to the number crustal-scale seismic profiles available, the major emphasis during the compilation of Central Appalachian Transect was on interpretations of the seismic data.