Rb–Sr whole rock isochrons from several suites of granite boulders which occur in Ordovician and Silurian conglomerates in the Southern Uplands of Scotland yield ages of around 1200 Ma, 600 to 700 Ma and 470 to 490 Ma. The plutonic and tectonic history recorded by these clasts corresponds more closely with that of NW Newfoundland than with that of Scotland. The petrography of the clasts can also be matched with exposed granite plutons in Newfoundland. Since the conglomerates were derived from the NW it is concluded that the Southern Uplands lay to the SE of Newfoundland. A total of 1500 km strike-slip displacement occurred between the Caradoc and the Early Devonian, consistent with oblique subduction of the Iapetus Ocean below the North American continental margin.