THAMES, the chief river of England, rising in several small streams among the Cotswold Hills in Gloucestershire. Its source is generally held to be at Thames Head, in the parish of Coates, 3 m. west of Cirencester; but claims have also been advanced on behalf of the Seven Springs, the head waters of the river Churn, 5 m. south of Cheltenham. The length of the river from Thames Head Bridge to London Bridge is 1614 m. and from London Bridge to the Nore, 47 4 m., a total of 209 m. The width at Oxford is about 150 ft., at Teddington 25o ft., at London Bridge 750 ft., at Graves end 2,100 ft., and between Sheerness and Shoeburyness, immedi ately above the Nore, 52 m. The height of Thames Head above sea-level is 356 ft., Seven Springs 700 ft., and Lechlade 237 ft. and the average fall below Lechlade is 20 in. per mile. The Thames forms the boundary between the following counties along its course : Gloucestershire and Wiltshire, Gloucestershire and Berkshire, Oxfordshire and Berkshire, Buckinghamshire and Berk shire, Middlesex and Surrey, and finally, at its estuary, Essex and Kent. In the succeeding paragraph the bracketed figures indicate the distance in miles above London Bridge.
The upper course lies through a broad valley. The scenery is rural and pleasant; the course of the river winding. Before reaching Oxford the stream swings north, east and south to encircle the wooded hills of Wytham and Cumnor, which over look the city from the west. The Windrush joins from the north (left) at New Bridge (126i), the Evenlode near Eynsham 19), and the Cherwell at Oxford (112). Between Lechlade and Oxford the main channel sends off many narrow branches ; the waters of the Windrush are similarly distributed, and the branches in the neighbourhood of Oxford form the picturesque "backwaters." The river then passes the pleasant woods of Nuneham, and at Abingdon (loll) receives the Ock from the Vale of White Horse, at Dorchester (954) the Thame (left), and it then passes Walling ford and Goring (85). The river now bends eastward, and breaches the chalk hills, dividing the Chilterns from the downs of Berkshire. From this point as far as Taplow the southern slopes of the Chilterns descend closely upon the river; they are finely wooded, and the scenery is peculiarly beautiful. At Pang bourne (8o4) the Thames receives the Pang (right), and at Reading (742) the Kennet (right). After passing Reading it bends northward to Henley (65), eastwards past Great Marlow (57) to Bourne End (54), and southwards to Taplow and Maiden head (49-1), receiving the Loddon (right) near Shiplake above Henley. Winding in a south-easterly direction, it passes Eton and Windsor (433-), Datchet (4'1), Staines (36), Chertsey Shepperton (30) and Sunbury (262), receiving the Coln (left) at Staines, and the Wey (right) near Shepperton. Flowing past
Hampton Court, opposite to which it receives the Mole (right), and past Kingston (2o1), it reaches Teddington OW. Passing Richmond (i6) and Kew the river flows through London and its suburbs for a distance of about 25 m., till it has passed Wool wich. Gravesend, the principal town below Woolwich, is 261 rn.
from London Bridge. The estuary may be taken to extend to the North Foreland of Kent. In the tideway the principal affluents of the Thames are the Brent at Brentford, the Wandle at Wands worth, the Ravensbourne at Deptford, the Lea at Blackwall, the Darent just below Erith, and the Ingrebourne at Rainham, besides the Medway.
The basin of the Thames is of a composite character. Thus, the upper portion of the system, above the gap at Goring, is a basin in itself, defined on the west and south by the Cotswold and White Horse Hills and on the east and north by the Chilterns and the uplands of Northamptonshire. But there are several points at which its division from other river basins is only marked by a very low parting. Thus a well-marked depression in the Cotswolds brings the head of the (Gloucestershire) Coln, one of the head-streams of the Thames, very close to that of the Isborne, a tributary of the upper Avon; the parting between the head streams of the Thames and the Bristol Avon sinks at one point, near Malmesbury, below 30o ft.; and head-streams of the Great Ouse rise little more than two miles from, and only some 30o ft. above, the middle valley of the Cherwell. The White Horse Hills and the Chilterns strike right across the Thames basin, but almost their entire drainage from either flank lies within it, and similarly a great part of the low-lying Weald, though marked off from the rest of the basin by the North Downs, drains into it through these hills. Further, the Kennet continues upward the line of the main valley below the Goring gap, and the Cherwell that of the main valley above it. The basin thus presents interesting prob lems. The existence of wide valleys where the small upper waters of the Cherwell, Evenlode and Coln now flow, the occurrence of waterborne deposits in their beds from the north-west of England and from Wales, and the fact that the Thames, like its lower southern tributaries which pierce the North Downs, has been able to maintain a deep valley through the chalk elevation at Goring, are considered to point to the former existence of a much larger river, in the system of which were included the upper waters of the present Severn, Dee and other rivers of the west. The question, in fact, involves that of the development of a large part of the hydrography of England.