Scotland's geological foundations

The foundations of Scotland are five distinct geological blocks that were brought together in a series of continental collisions around 480 to 425 million years ago. Prior to this period of continental collision, Scotlands foundation blocks lay far apart.

The Northwest Sea-board lay to the west with the Northern Highlands some 100 km or so to the east. The beginnings of the Grampian Highlands were even further away, lying perhaps 200 km to the south. All these areas were part of the edge of a large continent called Laurentia.

South of Laurentia was the wide Iapetus Ocean, which formed around 500 million years ago, but was getting steadily narrower due the forces of continental drift. As the Iapetus Ocean closed, three land masses collided with Laurentia. This series of continental collisions (480-425 million years ago) is know as the Caledonian mountain-building event or Caledonian Orogeny. It formed a mountain range, of Alpine, or even possibly Himalayan proportions, known as the Caledonian Mountains. The remains of this mountain range stretch from Norway to the Appalachian Mountains of North America.

The Caledonian Orogeny began when a chain of volcanic islands, formed in the Iapetus, collided with Laurentia (the Grampian Event). The remains of this island chain are believed to form the foundations of the Central Belt. The second stage of the Caledonian Orogeny was the collision of Baltica (Scandinavian Europe) with the northeast edge of Laurentia (the Scandian Event). This brought the Northern Highlands and Northwest Sea-board together. It also started the process of side-ways movement which eventually brought the Northern Highlands and Grampian Highlands together.

The final stage of the Caledonian Orogeny was the less violent collision of Eastern Avalonia (containing England) to the south. This involved the scrapping up of a huge pile of sea-floor sediments which now form the Southern Uplands and occurred around 425 million years ago. Thus by around 425 million years ago, Scotlands geological foundations had come together.

The Iapetus Ocean and the Caledonian Orogeny

An ocean called the Iapetus once existed between Scotland and England. Its closure precipitated the Caledonian Orogeny.

The Grampian Event of the Caledonian Orogeny

The first stage of Caledonian Orogeny was the Grampian Event. This predominantly affected the Grampian Highlands.

The Scandian Event of the Caledonian Orogeny

The second stage of the Caledonian Orogeny was the Scandian Event. This predominantly affected the Northern Highlands

Collision with England in the Caledonian Orogeny

The final stage of the Caledonian Orogeny was the collision of Scotland and England. This created the Southern Uplands.