Thames， river in southern England， the most important river in England. It rises in four headstreamsheadstream n.源头， 发源地 - the Isis， the Churn， the Colne， and the Leach - on the southeastern slope of the Cotswold Hills， in Gloucestershire， near Cheltenham. The streams convergeconverge v.聚合， 集中于一点 vt.会聚 on Oxford and flow generally southeast to Reading， through a gap in the Chiltern escarpment. The Thames thereafter follows a generally eastern course through London， and a few kilometers below Gravesend it expands into a wide estuaryestuary n.河口， 江口 and enters into the North Sea. It is 338 km (210 mi) long. At London Bridge the width of the river is about 265 m (about 870 ft)； at Woolwich， 448 m (1470 ft)； at Gravesend pier 732 m (2400 ft)； 5 km (3 mi) below Gravesend， 1180 m (3870 ft)； at Nore Light 10 km (6 mi)； and at its mouth， between Whitstable and Foulness Point， the estuary is 29 km (18 mi) across.
The London docks cover more than 56 km (35 mi) of the river from the Tower Bridge to Tilbury Dock， and oceangoingoceangoing adj.远洋航行的 vessels are moored here. Although the upriver docks are tidal， the lower admit any vessel at any stage of the tide. The Tilbury docks， closed in 1981， have been redeveloped into an area of light industry.
The Thames is the main source of the water supply of London. The part of the river immediately below London Bridge is called the Pool， and the part between the bridge and Blackwall is called the Port. Two embankmentsembankment n.堤防， 筑堤 have been formed， one on the northern shore from Blackfriars Bridge to Westminster and one on the southern shore from Westminster Bridge to Vauxhall. In the Middle Ages the valley was prosperous， with many famous religious houses and several large towns， including Oxford， Reading， and Windsor. Interesting archaeological discoveries were made in the valley， including fossils of seashells and a human skull of the Paleolithic period. Severely polluted in the 19th century， the river was made cleaner beginning in 1963. In 1982 downstreamdownstream adv.下游地 adj.下游的 barriers， designed to protect London from floods caused by extreme high tides， were completed.
From over 600，000 years ago， during the Pleistocene ice age， until the Anglian glaciation around 475，000 years ago， the early River Thames flowed from Wales to ClactononSea， and crossed what is now the North Sea to become a tributary of the Rhine. The river followed a path through Buckinghamshire， the southern part of Hertfordshire and Essex， running from the area of modern Staines up the valley of the Colne to Hatfield and then eastward across Essex towards the primeval Rhine. It was later diverted by encroaching ice down the valley of the modern River Lea to its present estuary position. This path was then itself blocked by a mass of ice near Hatfield and a lake ponded up to the west of this around St. Albans. Waters eventually overflowed near Staines to cut the path of the modern Thames through central London. When the ice retreated about 400，000 years ago the river bed along the new route followed the lower path and so the river remained on its present day course. The flow in the Colne valley then reversed， now flowing south as a tributary into the modern Thames. Superficial gravel depositsdeposit n.堆积物， 沉淀物， 存款， 押金， 保证金， 存放物 vt.存放， 堆积 vi.沉淀 from the primordial Thames are found throughout the Vale of St. Albans.
Course
The Thames has a length of 346 km (215 miles). Its source is about a mile north of the village of Kemble， near Cirencester in the Cotswolds； it then flows through Oxford (where it is called the Isis， a truncationtruncation n.切断 of Tamesis， its Latin name)，Wallingford，Reading， HenleyonThames， Marlow， Maidenhead， Eton and Windsor and London.
The Thames rises in Gloucestershire， traditionally forming the county boundary， firstly between Gloucestershire and Wiltshire， between Berkshire on the south bank and Oxfordshire on the north， between Berkshire and Buckinghamshire， between Berkshire and Surrey， between Surrey and Middlesex， and between Essex and Kent. Before the 1974 boundary changes， the current boundary between Berkshire and Surrey was between Buckinghamshire and Surrey. The Thames is still used as an administrative border， though less so than it has been.
From the outskirts of Greater London， it passes Syon House， Hampton Court， Richmond (with the famous view of the Thames from Richmond Hill) and Kew， before it passes through London proper， then Greenwich and Dartford and entering the sea in a drowned estuary， The Nore. Part of the area west of London is sometimes termed the Thames Valley whilst east of Tower Bridge development agencies and Ministers have taken to using the term Thames Gateway.
