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The Three Counties System is a set of inter-connected limestone solutional cave systems spanning the borders of Cumbria, Lancashire, and North Yorkshire in the north of England. The possibility of connecting a number of discrete cave systems in the area to create a single super-system that spans the county borders was first proposed by Dave Brook in 1968, and it was achieved in 2011. The system is currently over long, making it the longest in the UK and the twenty sixth longest in the world, and there continues to be scope for considerably extending the system.〔 ==Description== The Three Counties System most southerly entrance is currently Large Pot (, NGR SD 6281 7685) on the northerly flank of Kingsdale in North Yorkshire, and the most northerly entrance is currently Bull Pot of the Witches (, NGR SD 6623 8131) beneath Barbon Low Fell in Cumbria - a distance of almost . Between the two, the system passes beneath Ireby Fell and Leck Fell which are in Lancashire. The system runs mainly north-south, its western extent being limited by the Craven Fault which truncates the limestone exposure, and the eastern extent where the limestones are conformable overlain by younger rocks. Streams flow from the higher topography from the east and sink into swallet holes at the edge of the limestone. The Three Counties System contains a number of major subterranean streams, all of which combine to resurge at Leck Beck Head above Cowan Bridge. At the northern end, swallets in Barbondale close to the Dent Fault drain south-west through Bull Pot of the Witches, and the water enters the Ease Gill Caverns system in Lancaster Hole; most of Ease Gill Beck to the south drains into the extensive Ease Gill Caverns, although some drains into Link Pot and thus into the bottom of Pippikin Pot; most of Leck Fell drains into the Leck Fell Master Cave, which is part of Lost Johns' Cave, although some drains into Gavel Pot, and some into Notts Pot; Ireby Fell in the south drains into Notts Pot. All these streams eventually reach the phreatic zone where exploration is only possible by cave diving.〔 Some small streams in the south of The Three Counties System are known to resurge at Keld Head in Kingsdale, the next valley to the south. The system is very complex, with sections formed at different times when the landscape topography and drainage patterns were different from today. Some of the system is believed to have been formed during the Hoxnian Stage (marine isotope stage 11), with one stalagmite in Lancaster Hole being dated to over 350,000 years old, whilst other sections are still being formed today. Waltham has identified five distinct phases of development. The Leck Beck Catchment Area Site of Special Scientific Interest, which is based around the catchment area of the Three Counties System, states in its reason for notification: ''"The scale and variety of the caves makes this a most important site for the study of surface and underground landform development over a long period of the recent past."''〔(【引用サイトリンク】url=https://designatedsites.naturalengland.org.uk/SiteDetail.aspx?SiteCode=S1001420&SiteName=beck&countyCode=9&responsiblePerson= )〕 It is the interconnections between the sections that are the key to the existence of the super-system. The Three Counties System is deep. The highest point is the entrance to Large Pot which is at an altitude of , and the lowest point is in Gavel Pot where the upstream sump has been dived to a depth of , an altitude of . 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「Three Counties System」の詳細全文を読む スポンサード リンク
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