Isostatic flexure has left dome and basin arching of craton as Transcontinental Arch down center of US from lowlands of Canadian Shield, which exists at this point as peninsula and island chain eroding into shallow seas covering east and west. Ouachita Terrane transfers from southern margin of Laurentia to become part of Andes. Sauk Sequence of shallow sea transgressions peaks at end of Cambrian, subsiding by mid Ordovician, just before Taconic orogeny. Taconian orogeny via Iapetus Sea subduction zone volcanic island arcs colliding with margin initiates Appalachians in Maritimes, exceeding 4,000 feet, includes Logan's thrust fault in Newfoundland. Sea transgressions immediately resume with Tippecanoe sequence, including huge reef developments in Great Lakes Region.
Tippecanoe sequence ends, major erosional period begins.
Forestation of land begins. Acadian highlands erode to create huge chain of Catskill Deltas and basin expanding westward. Transcontinental arch and Canadian shield on either side of middle seaway remain unsubmerged. Volcanic island arcs arise along subduction zone on margin from Arctic to Mexico, eroding into back-arc shelf. Mid Devonian West coast is peninsula stretching north from Montana with seaway through Alberta and southern Sask.