Abstract The Lake District, Isle of Man and Leinster basins lie within the Leinster–Lakesman Terrane, which is situated between the Monian Terrane and the Iapetus Suture ( Fig. 5.2 ). It is sometimes convenient to refer to the Isle of Man and Lake District pre-Caradoc basins together as the Lakesman Basin because they have a similar early Ordovician history characterized by a thick accumulation of mudrocks and turbidites, although the basins may have been separate entities. Following the early phase of basin evolution there was an extensive development of volcanism in the Lake District. The mildly alkali tholeitic composition of the volcanic rocks of the Eycott Group might reflect an immature volcanic arc built on a thin outer edge of the continent. The Borrowdale Volcanic Group records the climactic phase of arc volcanism. After the end of most, but not all, volcanic activity the Lake District Basin subsided, accommodating a thick sequence of clastic sediments in what is interpreted as a foreland basin, which filled and shallowed in its final stages. The Lakesman terrane was subsequently deformed during the Acadian Orogeny (Chapter 4).