The varied rocks and landscape of the British Isles result from their position at one of the Earth’s geological crossroads (Fig. 2.1). Seven large fragments of continental crust influenced the Phanerozoic geological history of this area, even before the Mesozoic formation of the Atlantic Ocean. This section briefly reviews this history in terms of a sequence of crustal shortening and extension events (Fig. 2.2). This event framework largely determines the succession and distribution of rock units in the British Isles (Ch. 2.2)

Until Silurian time, the north and south of the British Isles were geographically separate. Scotland and northwest Ireland were part of Laurentia in low southern latitudes (Fig. 2.2c). These areas had a complex early history dating back at least 2 000 million years before the Cambrian period. The Grampian orogeny was merely the last of a series of Precambrian events that deformed and metamorphosed the Laurentian crust (Fig. 2.2a). The Athollian orogeny further heated and uplifted the Laurentian continental margin in Ordovician time.