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Durdle Door (sometimes written Durdle Dor) is a natural limestone arch on the Jurassic Coast near Lulworth in Dorset, England.〔West, I.W., 2003. "(Durdle Door; Geology of the Dorset Coast )". Southampton University, UK. Version H.07.09.03.〕 It is privately owned by the Welds, a family who owns in Dorset in the name of the Lulworth Estate.〔(【引用サイトリンク】url=http://www.purbeck-gazette.co.uk/news/info.aspx?f=885 )〕 It is open to the public. The name Durdle is derived from the Old English 'thirl' meaning bore or drill. ==Geology== The form of the coastline around Durdle Door is controlled by its geology—both by the contrasting hardnesses of the rocks, and by the local patterns of faults and folds.〔Nowell, D. A. G. "The geology of Lulworth Cove, Dorset." Geology Today 14 (1998): 71–74.〕 The arch has formed on a concordant coastline where bands of rock run parallel to the shoreline. The rock strata are almost vertical, and the bands of rock are quite narrow. Originally a band of resistant Portland limestone ran along the shore, the same band that appears one mile along the coast forming the narrow entrance to Lulworth Cove.〔(【引用サイトリンク】title=Lulworth Cove & Crumple - a geography pilgrimage )〕 Behind this is a band of weaker, easily eroded rocks, and behind this is a stronger and much thicker band of chalk, which forms the Purbeck Hills.〔 These steeply dipping rocks are part of the geological structure known as the Lulworth crumple, itself part of a broader monocline (a kinked type of geological fold) produced by the building of the Alps during the mid-Cenozoic.〔〔 The limestone and chalk are in closer proximity at Durdle Door than at Swanage, to the east, where the distance is over .〔Arkell, W. J., 1947. The geology of the country around Weymouth, Swanage, Corfe and Lulworth. Mem. geol. Surv. UK〕 There are at least three reasons for this. Firstly, the beds are highly inclined (whilst more gently inclined at Swanage). Secondly, some of the beds have been cut out by faulting; and thirdly, the area around Durdle Door seems to have had shallower water at the time of deposition than comparable geological sections, so thinner bands of sediments were deposited. Around this part of the coast nearly all of the limestone has been removed by sea erosion, whilst the remainder forms the small headland which includes the arch. Erosion at the western end of the limestone band has resulted in the arch formation.〔 UNESCO teams monitor the condition of both the arch and adjacent beach.〔(【引用サイトリンク】title=Monitoring the coast )〕 The isthmus which joins the limestone to the chalk is made of a band of Portland limestone, a narrow and compressed band of Cretaceous Wealden clays and sands, and then narrow bands of greensand and sandstone.〔Phillips, W. J. "The structures in the Jurassic and Cretaceous rocks on the Dorset coast between White Nothe and Mupe Bay." Proceedings of the Geologists' Association 75.4 (1964): 373-IN1.〕 In Man O' War Bay, the small bay immediately east of Durdle Door, the band of Portland and Purbeck limestone has not been entirely eroded away, and is visible above the waves as Man O'War Rocks.〔(【引用サイトリンク】title=Durdle Door, West of Lulworth Cove, Dorset. Geology of the Wessex Coast of Southern England )〕 Similarly, offshore to the west, the eroded limestone outcrop forms a line of small rocky islets called (from east to west) The Bull, The Blind Cow, The Cow, and The Calf.〔 As the coastline in this area is generally an eroding landscape, the cliffs are subject to occasional rockfalls and landslides; a particularly large slide occurred just to the east of Durdle Door in April 2013, resulting in destruction of part of the South West Coast Path. 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「Durdle Door」の詳細全文を読む スポンサード リンク
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