The Himalayan Mountain belt is an excellent example of collision of the Indian and Tibetan plates, and the present-day tectonic set-up of this mountain chain is a direct reflection of the deformation processes that operated during and after the collision. The Himalayan foreland basin has developed in the frontal part of the orogen, and the sediments deposited in the Himalayan foreland basin are preserved almost continuously along the Himalayan foothills for a distance of about 2400 km from Jammu in the west to Arunachal Pradesh in the east and is named as the Siwalik Group. It is delineated by the Lesser Himalaya to the north and Indo-Gangetic Plain to the south, and tectonically, it is found between the Main Boundary Thrust (MBT) in north and the Main/Himalaya Frontal Thrust (MFT/HFT) in south. In the Darjeeling-Sikkim Himalaya, the Siwalik sediments are found as narrow strip along the foothill parts of Darjeeling and Kalimpong hills and to north of the Tista fan deposits.