Collision with England
The Caledonian Orogeny’s final stage saw Scotland and England collide. This part of the mountain-building event created the Southern Uplands.
Eastern Avalonia collided with Laurentia about 425 million years ago, joining England and Scotland.
This collision was less violent than those that led to the Grampian Event and the Scandian Event, and didn’t cause huge amounts of rock deformation. The process of soft collision is sometimes called ‘soft docking’.
As the Iapetus Ocean closed, the ocean floor was pushed down (subducted) below Laurentia’s southern edge. Sediment scraped off this ocean floor created a huge pile – known as an accretionary prism – which now forms the Southern Uplands.
The northern edge of Eastern Avalonia, marked by the Iapetus Suture, lies buried beneath younger sediments just south of the Scotland–England border.
About 400 million years ago, molten magma derived as a result of the collision and loss of the ocean gave rise to the granites of Criffel and Cairnsmore in the Southern Uplands.
Find out more about the geological foundations of the Southern Uplands.