The Evolution of Britain’s Landscape.

Britain and Scotland come together: Ordovician(510-439 Ma.) 
and Silurian (439-408 Ma.) ( Lower Palaeozoic) times. Part 1 of 3

During Ordovician times, most of Scotland and N. Ireland were separated from England & Wales by a wide ocean called Iapetus.

Scotland and northern Ireland formed part of an ancient continent called Laurentia, now N. America while England, Wales & Southern Ireland formed part of a continent called Avalonia which was about 27 deg. south of the equator. (See diagrams).

The Skiddaw Slates (or Skiddaw Group) of the Lake District consist of metamorphosed marine sediments laid down on the northern margin of Avalonia. These slates can now be seen in the northern part of the Lake District, e.g. around Blencathra and Skiddaw. Have a look at some chiastolite slate.

Above: Paleomap from “The Geology of Britain. An Introduction” Peter Toghill. 2000. Swan Hill Press. (cf. Recommended Reading for more information about this book.)

The map, above left, shows the disposition of the continents during Early Ordovician times. “England, Wales and Southern Ireland” (Avalonia) are separated from “Scotland and Northern Ireland” by the spreading Iapetus Ocean during late Precambrian, Cambrian times. The photo below shows pillow lavas formed from the mid ocean ridge as the ocean spread. They can be seen on Llanddwyn Island (SH386627) Anglesey.

During Late Ordovician times the Iapetus Ocean began to close, initiating a subduction zone resulting in the volcanic rocks of the Lake District (the Borrowdale Volcanic Group).

The photo to the left is Thornton Force (on the Ingleton Glens Walk). The lower half of the cliff consists of turbidites (sediments consisting of ill-sorted sandstones/siltstones) originally laid down horizontally in the expanding Iapetus Ocean in early Ordovician (Cambrian?) times. The sediments were subsequently folded and uplifted as the Iapetus Ocean closed resulting in steeply dipping sediments.After a long period of erosion (about 170 million years) the overlying Lower Carboniferous limestones were then deposited creating the famous unconformity that is seen today.

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