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River Wear
The River Wear (pronounced ) in North East England rises in the Pennines and flows eastwards, mostly through County Durham to the North Sea in the City of Sunderland. At long, it is one of the region's longest rivers, wends in a steep valley through the cathedral city of Durham and gives its name to Weardale in its upper reach and Wearside by its mouth.
==Geology==
The Wear rises in the east Pennines, an upland area raised up during the Caledonian orogeny. Specifically, the Weardale Granite underlies the headwaters of the Wear. Devonian Old Red Sandstone in age, this Weardale Granite does not outcrop but was surmised by early geologists, and subsequently proven to exist as seen in the Rookhope borehole.〔(【引用サイトリンク】url=http://www.pastperfect.org.uk/sites/oldrookhope/archive/40.html )〕 It is the presence of this granite that has retained the high upland elevations of this area (less through its relative hardness, and more due to isostatic equilibrium) and accounts for heavy local mineralisation, although it is considered that most of the mineralisation occurred during the Carboniferous period.
It is thought that the course of the River Wear, prior to the last Ice Age, was much as it is now as far as Chester-le-Street. This can be established as a result of boreholes, of which there have been many in the Wear valley due to coal mining. However, northwards from Chester-le-Street, the Wear may have originally followed the current route of the lower River Team. The last glaciation reached its peak about 18,500 years ago, from which time it also began a progressive retreat, leaving a wide variety of glacial deposits in its wake, filling existing river valleys with silt, sand and other glacial till. At about 14,000 years ago, retreat of the ice paused for maybe 500 years at the city of Durham. This can be established by the types of glacial deposits in the vicinity of Durham City. The confluence of the River Browney was pushed from Gilesgate (the abandoned river valley still exists in Pelaw Woods), several miles south to Sunderland Bridge (Croxdale). At Chester-le-Street, when glacial boulder clay was deposited blocking its northerly course, the River Wear was diverted eastwards towards Sunderland where it was forced to cut a new, shallower valley. The gorge cut by the river through the Permian Magnesian Limestone can be seen most clearly at Ford Quarry. In the 17th edition of Encyclopædia Britannica (1990), reference is made to a pre-Ice Age course of the River Wear outfalling at Hartlepool.
The upland area of Upper Weardale retains a flora that relates, almost uniquely in England, to the end of the last Ice Age, although it almost or entirely lacks the particular rarities that make up the unique "Teesdale Assemblage" of post-glacial plants. This may, in part, be due to the Pennine areas of Upper Weardale and Upper Teesdale being the site of the shrinking ice cap. The glaciation left behind many indications of its presence, including lateral moraines and material from the Lake District and Northumberland, although surprisingly few drumlins. After the Ice Age, the Wear valley became thickly forested, however during the Neolithic period and increasingly in the Bronze Age, were largely deforested for agriculture.
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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