The late Precambrian and early Palaeozoic ocean that lay between Baltica and Laurentia. The oceanic crust and upper mantle of the Iapetus Ocean floor is presumed to have been subducted during the early Palaeozoic, and the ocean to have disappeared completely by the latest Silurian–early Devonian (about 400 Ma ago). The ancient suture is thought to extend from WSW to ENE across the Solway Firth and Borders Region, Scotland. The Caledonian orogenic belt, which removed all trace of the Iapetus Ocean, extends all along the border between the two ancient cratons, affecting the areas now known as Norway, eastern Greenland, Scotland, northern England, Wales, Ireland, eastern Canada, and the eastern USA.