|
Brean Down is a promontory off the coast of Somerset, England, standing high and extending into the Bristol Channel at the eastern end of Bridgwater Bay between Weston-super-Mare and Burnham-on-Sea. Made of Carboniferous Limestone, it is a continuation of the Mendip Hills. Two further continuations are the small islands of Steep Holm and Flat Holm. The cliffs on the northern and southern flanks of Brean Down have large quantities of fossils laid down in the marine deposits about 320–350 million years ago. The site has been occupied by humans since the late Bronze Age and includes the remains of a Romano-Celtic Temple. At the seaward end is Brean Down Fort which was built in 1865 and then re-armed in the Second World War. Brean Down is now owned by the National Trust, and is rich in wildlife, history and archaeology. It is a Site of Special Scientific Interest due to both the geology and presence of nationally rare plants including the white rock-rose. It has also been scheduled as an ancient monument. ==Geology== The Mendip Hills, of which Brean Down forms the most westerly part, are the most southerly Carboniferous Limestone upland in Britain. These rock strata were laid down during the early Carboniferous period, about 320–350 million years ago. Subsequently, much of northwestern Europe underwent continental collision throughout the late Paleozoic era, culminating in the final phases of the Variscan orogeny near the end of the Carboniferous period, 300 million years ago. This tectonic activity produced a complex suite of mountain and hill ranges across what is now southern Ireland, south-western England, Brittany, and elsewhere in western Europe.〔(【引用サイトリンク】title=GCR block – Variscan Structures of South-West England )〕 As a result of the Variscan mountain-building, the Mendip area now comprises at least four anticlinal fold structures, with an east-west trend, each with a core of older Devonian sandstone and Silurian volcanic rocks. West of the main Mendip plateau the Carboniferous Limestone continues in Bleadon Hill and Brean Down, and on the islands of Steep Holm and Flat Holm. Brean Down is just over long and runs in an east-west direction near the mouth of the River Axe opposite Uphill Cliff. The flat area on the top of the peninsula may represent a raised bench laid down when the sea level was much higher than it is today, as the highest point of the promontory is approximately above sea level. The cliffs on the north and south faces are rich in fossils that include corals, seashells and crinoids, which supports the theory of the marine deposition of the rocks. 13 separate layers have been identified in the 'sand cliff' on the south side, the lowest five dating to the millennia of the last glaciation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Brean Down」の詳細全文を読む スポンサード リンク
|