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Horsham Stone
Horsham Stone is a type of calcerous, flaggy sandstone containing millions of minute sand grains and occurring naturally in the Wealden clay of the English county of West Sussex.〔Sussex Stone, The Story of Horsham Stone and Sussex Marble, Roger Birch, 2006, ISBN 978-0-9551259-0-4〕 It is also high in mica and quartz. The rock extends in an arc-like formation for several kilometres around the town of Horsham from which it takes its name, and lies just below the Wealden clay surface in bands thick.〔 Horsham Stone is famous for its ripple-marked appearance, formed by the action of the sea similar to the ripples on the sandbanks and beaches of Sussex.
==Formation==
Sussex Stone and its limestone equivalent Sussex Marble were formed around 130 million years ago in the Lower Cretaceous period when Britain was quite different from the shape it is today. It is estimated that the latitude for Britain was approximately 30 degrees north of the equator.〔 The fossil evidence in Horsham Stone and Sussex Marble indicate a diversity of life living on a broad, flat subtropical landscape.Towards the end of the Cretaceous period around 90 million years ago, most of Britain including Sussex would have been submerged beneath a tropical sea that was depositing chalk.
The sediments of the Wealden Basin were buried under hundreds of metres of further sediment over the next 100 million years and were then uplifted gradually by platetonic movement and then eroded to expose Wealden rocks. Horsham Stone would have been visible to early settlers after the Ice Age around 12,000 years ago. When quarried, Horsham Stone could be extracted in "flat grey slabs of varying thickness".〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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