Figure 2: Northwest-southeast regional cross sections through the passive margin of eastern North America. Sections show Paleozoic structures, early Mesozoic rift basins, and Mesozoic-Cenozoic postrift basins. Vertical axes are in two-way travel time. Section locations are shown in Figure 1. (a) Transect through southeastern Canada is based on seismic data from Keen et al. (1991a, b) and Withjack et al. (1995). Transect through the eastern United States is based on geologic data from Shaler and Woodworth (1899), Benson and Doyle (1988), and Olsen et al. (1989), and seismic data from Sheridan et al. (1993). Onshore geology was converted to two-way travel time assuming a velocity of 4000 m/s. (c) Transect through the southeastern United States is based on seismic data from Behrendt (1986), Austin et al. (1990), and Oh et al. (1995). Eastern U.S. and southeastern U.S. transects show massive volcanic wedges (SDR's) at continent-ocean boundary. [Modified from Withjack et al., 1998.]