By 750 Ma Rodinia was splitting apart and the first of the cover rocks we see in Shetland, the sediments that became the Moine Supergroup, had been laid down (Fig. 3a). There is an ongoing debate as to the tectonic history leading to deposition of the Moine Supergroup and to the nature of its basement gneisses. The ‘traditional’ view is that basement gneisses are Lewisian and sedimentation was in rift basins along the margin of Laurentia during the separation of Baltica from Rodinia. It is also argued however, that the Moine rocks and their basement are an exotic terrane accreted onto the Laurentian margin, having being originally part of either Baltica or ancient South America.