The outermost range of Himalayas is Shiwaliks. They extend over a width of 10-50 km and have an altitude varying between 900 and 1100m. These ranges are composed of unconsolidated sediments brought down by rivers from the main Himalayan ranges. These valleys are covered with thick gravel and alluvium. The longitudinal valley lying between Lesser Himalaya and the Shiwaliks are known as Duns.