Virtual Geology

Why are there 282 3,000 ft mountains in Scotland, but only 15 in Wales and 6 in England. The reason is that Scotland has a very different geological history than England and Wales. In fact, it is believed that 500 million years ago, they belonged to two different continents. Scotland and parts of north west Ireland were part of a continental plate called Laurentia (named after the St Lawrence River), which contained most of what is now North America, while England and Wales belonged to a micro-continent called Avalonia (named after the Avalon Peninsular in Newfoundland), along with parts of the far west of the European mainland and south eastern Ireland as well as parts of Newfoundland and western North America. The continents had previously been separated by an ocean (the Lapetus Ocean) that, over millions of years closed up, as the continents drifted towards each other.

The two continents collided along with a third continent called Baltica in the late Silurian and Early Devonian period (about 490 to 390 million years ago) which resulted in a mountain building era called the Caledonian Orogeny. It was during this era that the mountains of Scotland, Snowdonia and the Lake District were built by volcanic activity and the folding of rocks resulting from the crashing together of the continents. This was analogous to the much later building of the Alps and the Himalayas. It is thought that the Scottish Highlands were once as tall as the Alps, but have subsequently been eroded. After the collision came a splitting (starting about 150 million years ago), as a new ocean (the Atlantic) formed. But there was an exchange of partners with Scotland now remaining attached to England and other parts of Avalonia ending up on the North American plate.

The reason this rather strange geological history is believed is that the fossil record in various layers of rocks in England, Scotland, south eastern and north western Ireland and in Western Europe and North America are very similar and because of this, it is believed that at different times, diferent land masses were attached to each other, detached and re-attached. You can view an animation, centred on Britain, of this movement of continental plates below:

Cambridge Earth Sciences: Continental drift animation

 

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