Caledonian mountain-building event

These diagrams are schematic cross-sections through the Earth’s crust at two different periods of geological time. The first is from the Ordovician period (around 460 million years ago) and shows the area that is now the Isle of Man lying on the margin of a small landmass called Avalonia which in turn forms part of the massive continent of Gondwana. North of Avalonia is the Iapetus Ocean which separates Gondwana from the northern continent of Laurentia.

Iapetus Ocean 460 Million years ago

of kilometres


By the process of continental drift, Avalonia gradually moved northwards and collided with Laurentia approximately 410 million years ago, as shown in the second diagram. This tectonic event has crumpled the rocks and formed the Caledonian mountain range. These mountains originally extended from North America to Scandinavia and equalled the size of the present day Himalayas. The Manx uplands represent part of the eroded remains of the mountains and most of the folds and faults visible in the Manx Group originate from this time.

Collision of Laurentia and Avalonia forms Caledonian Mountains
410 million years ago

After Watson and Dunning 1979