Ordovician(510-439 Ma.) and Silurian (439-408 Ma.) ( Lower Palaeozoic) times. Part 2 of 3

Description: Description: Description: Description: Description: Description: Subduction of ocean crust beneath Lake District; volcanoes resulting.

Subsequently, during Middle and Late Ordovician times, ocean crust began to be subducted beneath the Avalonian continent. This resulted in volcanic activity. The volcanic rocks consisting mainly of andesite lavas and tuffs are, with the exception of the Eycott Volcanics, exposed in the central part of the Lake District and provide some of the most dramatic scenery of the area. They are collectively known as the Borrowdale Volcanic Group.

During Silurian times volcanic activity ceased and deep water graptolitic mudstones, siltstones and greywackes, were deposited in the now closing Iapetus Ocean. These sediments, the Windermere Group, can now be seen in the southern part of the Lake District, e.g. around Lake Windermere. They provide a gentler type of scenery in contrast to the Borrowdale Volcanics.
Photo to the right: Graptolites:
Graptolites can be found in Silurian mudstones. Each was made up of many tiny individual animals, all linked together into a single colony. They were not attached to the sea floor, but floated near the surface of the seas.

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