DEHRA DUN  , a district of British India, in the Meerut division of the United Provinces . Its area is 1209 sq. m . The district is bounded on the N. by the native state of Tehri or Garhwal, on the E. by British Garhwal, on the S. by the Siwalik hills, which separate it from Saharanpur district, and on the W. by the hill states of Sirmur, Jubbal and Taroch . The valley (the Dun) has an area of about 673 sq. m., and forms a parallelogram 45 M. from N.W. to S.E. and 15 M. broad . It is well wooded, undulating and intersected by streams . On the N.E. the horizon is bounded by the Mussoorie or lower range of the Himalayas, and on the S. by the Siwalik hills . The Himalayas in the north of the district attain a height between 7000 and 8000 ft., one peak reaching an elevation of 8565 ft.; the highest point of the Siwalik range is 3041 ft. above sea-level . The principal passes through the Siwalik hills are the Timli pass, leading to the military station of Chakrata, and the Mohand pass leading to the sanatoriums of Mussoorie and Landaur . The Ganges bounds the Dehra valley on the E.; the Jumna bounds it on the W . From a point about midway between the two rivers, and neat the town of Dehra, runs a ridge which forms the watershed of the valley . To the west of this ridge the water collects to form the Asan, a tributary of the Jumna; whilst to the east the Suswa receives the drainage and flows into the Ganges . To the east the valley is characterized by swamps and forests, but to the west the natural depressions freely carry off the surface drainage .

Along the central ridge, the water-level lies at a

great depth from the surface (228 ft.), but it rises gradually as the country declines towards the great rivers . In 1901 the population was 178,195, showing an increase of 6 % in the decade . A railway to Dehra from Hardwar, on the Oudh and Rohilkhand line (32 m.), was completed in 1900 . The district is served by the Dun canals . Tea gardens cover a considerable area, and the valley contains a colony of European tea planters . History.—Dehra Dun only emerges from the mists of legend into authentic history in the 17th century A.D., when it formed part of the Garhwal kingdom . Towards the end of the century the heretical Sikh Guru, Rarn Rai, expelled from the Punjab, sought refuge in the Dun and gathered round him a crowd of devotees . Fateh Sah, raja of Garhwal, endowed the temple which he built, round which grew up the town of Gurudwara or Dehra (q.v.) . In the 18th century the fertility of the valley attracted the attention of Najib-ud-daula, governor of Saharanpur, who invaded it with an army of Rohillas in 1757 and annexed it to his dominion . His rule, which lasted till 1770, brought great prosperity to the Dun; but on his death it became a prey to the surrounding tribes, its desolation being completed after its conquest by the Gurkhas in 1803 . In 1814 it was taken possession of by the British, and in the following year was annexed to Saharanpur . Under British administration the Dun rapidly recovered its prosperity .