Lewisian Gneiss in Scotland
January 13, 2007
This cliff of exposed Lewisian Gneiss, at Oldshoremore in the far North West of Scotland, shows how the rocks were twisted under pressure deep in the Earth's crust, creating this striking pattern of black (basaltic) and pink (from granite) gneiss. Lewisian Gneiss is the oldest type of rock in Britain and was created about 3,000 million years ago. Some gneisses, as here at Oldshoremore, experienced further metamorphosis between 1,100 and 1,700 million years ago.
These ancient rocks in have counterparts in Canada and Greenland showing that Scotland once belonged to the same land mass, known as Laurentia. England and Wales belonged to a different land mass, Avalonia, which collided with Scotland approximately 430 million years ago when the Iapetus Ocean closed. The opening of the Atlantic Ocean (approximately 60 million years ago) and then the loss of the land bridge between England and France, at the end of the last ice age, finally created the British Isles as they are today, with Scotland well and truly stuck to England's "north coast!" See also the Earth Science Picture of the Day for October 18, 2006.