What features in the eastern united states are evidence for ancient continent-continent plate convergences?

Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together. But the separation of the continents was not a "neat" process: today a piece of Gondwanaland lies sunken beneath the eastern United States.