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Natural Tunnel State Park
Natural Tunnel State Park is a Virginia state park, centered on the Natural Tunnel, a massive naturally formed cave that is so large it is used as a railroad tunnel. It is located in the Appalachian Mountains near Duffield in Scott County, Virginia.
The Natural tunnel, which is up to wide and high,〔 began to form more than a million years ago when groundwater bearing carbonic acid percolated through crevices and slowly dissolved limestone and dolomite bedrock. A small river, which is now called Stock Creek, was diverted underground and it continued to erode the tunnel over many millennia.
The walls of the tunnel show evidence of prehistoric life. Many fossils have been found in the creek bed and in the tunnel walls.〔(【引用サイトリンク】title=Virginia State Parks: Natural Tunnel )〕
==Geology==
The tunnel passes through Purchase Ridge, which is made of the Ordovician Chepultepec Limestone and is near the axis of the Purchase Ridge syncline.〔Roadside Geology of Virginia, 1986, Keith Frye, Mountain Press Publishing Co.〕 It lies between the Clinchport Thrust Fault and the Hunter Valley Thrust Fault, on the Hunter Valley Thrust Sheet.〔Harris, L.D., 1965, The Clinchport thrust fault - a major structural element of the southern Appalachian Mountains: United States Geological Survey, Professional Paper 525-B, scale 1:543000.〕 The tunnel itself began its formation in the Pleistocene period.
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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