During the late Precambrian the Dalradian environment evolved from a relatively stable subsiding shelf into a series of fault-bounded blocks and basins. This increase in tectonic instability can be interpreted as a precursor to the continental rifting which led to the inception of the Iapetus Ocean at the end of the Precambrian, or base of the Cambrian, and was marked in the Dalradian terrain by the eruption of the Tayvallich Volcanics. A comparison of the late Precambrian history of the areas now adjacent to the Iapetus suture suggests that prior to this rifting the Greenland–northern Britain–NW Newfoundland area and Scandinavia formed part of the same plate with northern Norway lying close to northern Britain. As the evolution of all these areas was dominated by the opening of Iapetus during the Cambrian followed by closing initiated by subduction in the early Ordovician, many aspects of their history are similar. Southern Britain and SE Newfoundland, however, had a quite different late Precambrian history. They probably formed a microcontinental plate which originated at a considerable distance from northern Britain and which, until the closure of the Iapetus Ocean, was never in contact with the rest of the Caledonian belt.