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Northern Ireland Geology - Old Red Sandstone

Old Red Sandstone is a part of the Devonian period, between 17 and 354 million years ago. At that time Northern Ireland was an arid place with the newly formed Caledonian mountains to the northwest. These mountains were being eroded and large fans of sediment were formed at their edges. In places short-lived desert lakes were formed and rare fish fossils have been found in these sediments, for example in Lisbellaw, County Fermanagh.

These desert sediments eventually formed conglomerates and sandstones. They are exposed today in the Clougher Valley, and near to Cushendun, County Antrim where the conglomerates are of quartzite cobbles embedded in a matrix of red sandstone. These deposits are about 90 metres thick. Ripple marks and mud cracks reflect the origin of the sandstones which lie above the conglomerate.

Old Red Sandstone data Old Red Sandstone sample 

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