A middle to late Ordovician episode of mountain building, named after the Taconic Mountains (a N–S component of the Appalachian system to the east of the Hudson River, New York); it affected the whole of the Appalachians, in an area from what are now New England to eastern Canada, and is known locally in Newfoundland as the Humberian. In the south it was caused by the subduction of the western margin of the Iapetus Ocean, leading to the closing of the western basin of the Iapetus and the collision between N. America and the Piedmont microcontinent and the subsidence of the continental shelf further north. See appalachian orogenic belt.