Plate tectonic history of eastern North America for the last billion years shown in cross-sectional view at the approximate latitude of NJ. Oceanic crust is shown in red; pre-Grenville crust is mustard; crust created during Grenville orogeny is purplish-brown. "Island arc" and "Avalonia" are small continents that were added to North America during the Taconic and Acadian orogenies. b.y.=billion years; m.y.=million years. Modified from Marshak (2001).