The Windermere Supergroup is a geological unit formed during the Ordovician to Silurian periods ~450 million years ago, and exposed in the north west of England, including the Pennines and correlates along its strike, in the Isle of Man and Ireland, and down-dip in the Southern Uplands and Welsh Borderlands. It underlies much of north England's younger cover, extending south to East Anglia. It was formed as a foreland basin, in a similar setting to the modern Ganges basin, fronting the continent of Avalonia as the remains of the attached Iapetus ocean subducted under Laurentia.
The supergroup comprises the Coniston group of turbiditic limestones, and the overlying series of shales, grits and greywackes. Compression from the south east during the later Acadian orogeny (probably caused by the closure of the Rheic ocean) buckled the strata into anticlines and synclines and caused slaty cleavage in some sediment beds.
Read more about Windermere Supergroup: Before The Windermere: Basement Terranes, Sedimentation Begins: Filling The Basin, Beyond The Record: Postulated Cover, Modelling The Basin's Evolution, Matching The Model