district, administrative county of Oxfordshire, historic county of Berkshire, England, lying southwest of Oxford. It encompasses the northern part of the historic county of Berkshire. Its principal feature is a rich clay valley that lies north of the chalk Berkshire Downs. The vale stretches 17 miles (27 km) from Shrivenham to Abingdon and is drained by the River Ock, a tributary of the Thames. At Uffington the hills reach an elevation of 856 feet (285 metres) at Whitehorse Hill, on which a gigantic figure (374 feet 【114 metres】 long) of a horse is cut, the turf having been removed to reveal the white, chalky subsoil. It is of unknown origin and date but is certainly prehistoric. A number of other prehistoric remains occur in the vicinity, including the megalith (large standing stone) known as Wayland's Smithy. A prehistoric grassy track, the Ridge Way (one of the best walks in England), follows the crest of the hills. Other ancient tracks follow the foot of the escarpment, which is marked by a series of spring-line villages; in the centre is Wantage, the ancient market town that is said to be the birthplace (849) of Alfred the Great.

In addition to the vale itself, the predominantly rural district takes in the northern slopes of the Berkshire Downs and a considerable frontage on the River Thames. Abingdon, where the Ock flows into the Thames, is the site of the district's main administrative offices and is the largest town. The Atomic Energy Authority and the Agricultural Research Council maintain research establishments in the district, and automobiles and surgical instruments are manufactured. Area 224 square miles (581 square km). Pop. (2001) 115,632.