Idealized eastern North American rift basins. a) Idealized rift basin that formed mostly perpendicular to the extension (stretching) direction (red arrows). The border fault is somewhat oblique to the extension direction, but diabase dikes and intrabasinal faults are perpendicular to the extension direction. In longitudinal cross section (B-B'), the basin appears as a large syncline (downfold). It has a classic half-graben geometry in transverse cross section (A-A'). Note that the strata thicken toward the center of the basin (cross section B-B') and thicken toward the border-fault system (cross section A-A'). b) Idealized basin consisting of two large border-fault segments and associated synclinal subbasins separated by an intrabasinal high (anticline). c) Complex basin with a dip-slip border fault oriented perpendicular to the extension direction and a strike-slip to oblique-slip border fault oriented at a low angle to the extension direction. Modified from Schlische (1993) and Schlische et al. (2002).