Basement constitutes rocks which belong to a previous orogenic cycle which have been reactivated and incorporated into a younger cycle. Basement massifs may be classified according to their relative position in an orogen as external or internal massifs. They may also be categorized according to their role in deformation, as thrust-related, fold-related and composite massifs. All Appalachian external massifs were transported following removal from the overridden edge of the ancient North American continental margin. Most of the internal massifs are also probably transported, but several (Pine Mountain and Sauratown Mountains) may exist as windows exposing parauthochthonous basement beneath the main...