Silurian Period
Age : 417 to 443 million years ago
Geography, environment and climate
The time period covered by the Silurian documents the assembly of two continental elements and closure of the Iapetus Ocean to form the continental landmass from which the British Isles were later formed. England lay on the southern landmass (Avalonia). During the Lower Silurian the land of central and south-eastern England gave way to a shallow shelf sea along its margins. This sea deepened to the north so that the area now occupied by the Lake District was a deep-water basin. The Middle Silurian was marked by marine incursion across much of England and the Upper Silurian by the closure of the Iapetus Ocean, establishment of terrestrial conditions in the north and rapid shallowing of the shelf sea in the Midlands, Welsh Borders and southern England.
The British Isles lay at about 20-30 degrees south of the Equator and the climate was tropical to sub-tropical.
Key events
At the end of the Silurian, the Iapetus Ocean closed, and England and Scotland were joined together. This formed part of a wider series of collisions between the North American continent, southern Britain, the Baltic continent and various island arcs within the Iapetus Ocean during the late Ordovician and Silurian. These collisions resulted in a series of episodes of mountain building, which together are known as the Caledonian Orogeny. The resultant mountains, collectively known as the Caledonides, ran along the eastern side of North America, through Newfoundland, Scotland, Greenland and Scandinavia. The collision generated the folding, faulting and metamorphism (heat and pressure) of the affected rock successions. In Britain, all that remains of the Iapetus Ocean is a thick pile of deformed Ordovician and Silurian deep-sea sediments which now form the Southern Uplands of Scotland.
Rock types and occurrence in England
Deep-sea sandstones and mudstones outcrop in the southern Lake District. Along the Welsh Borders the sea was shallower and limestones and mudstones were deposited. These outcrop in Shropshire around Shelve, along Wenlock Edge to the Ludlow area and as small inliers scattered across the West Midlands, Worcestershire, Herefordshire, and Gloucestershire.
