The mainland consist of four well delined regions: (I) the great mountain zone, (II) the Indo-Gangetic Plains, (III) the desert region, and (IV) the Southem Peninsula.
The Himalayas comprise three almost parallel ranges interspersed with large plateaus and volleys, some of which like Kashmir and Kullu valleys are fertitle, extensive and of great scenic beauty. Some of the highest peaks in the world are to be found in these ranges. The high altitudes limit travel only to a few passes notably the Jelep La and Natu La on the main Indo-Tibet trade route through the Chumbi valley, north east of Darjeeling and shipki la in Stlej vallay north-west of Kalpa (Kinnour). The mountain wall extends over a distance of about 2,400 km with a varying depth of 240 to 320 km. in the east, between India and Burma and India and Bangladesh, the hill ranges are much lower. The Garo, Khasi, Jaintia and Nago hills running almost east-west, join the chain of the Mizo and Arakan hills running north-south.
The Indo-Gangetic plains, about 2,400 km long and 240 to 320 km broad are formed by the basins of three distinct river systems. The Indus, the Ganges and the Brahmaputra. They are one of the world’s greatest mass of flat alluvium and also one of the most densely populated areas on earth. There is hadly any variation in relief. Between the Yamuna river at Delhi and the Bay of Bengal, nearly 1,600 km away, there is a drop of only 200 metress in elevation.
The desert region can be divided in two parts: one the ‘great desert’ and the other ‘little desert’. The ‘great desert’ extends from the edge of Rann of Kutchh, beyond the Luni river northword. The whole of Rajasthan-Sind frontier runs through this . The ‘littledesert’ extends from the Luni river between Jaisalmer and Jodhpur up to the northern wastes. Between the great and little desert lies a zone of more or less absolutely sterile country. Consisting of rocky land cut up by lime stone ridges. Due to absence of surface water and very scanty rainfall, the region is almost absolutely sterile.
The Peninsular plateau is market off from the Indo-Gangetic plains by a mass of mountain and hill ranges varying from 460 to 1,220 mattress in height. Prominent amang these are Aravalli, Satprura, Maikala and Ajanta. The Peninsula is flanked on one side by the Eastern Ghats and the Arabian Sea lies a narrow coastal strip, while between the eastern Ghasts and the Bay of Bengal there is broader coastal area. The southern point of the plateau is formed by the Nilgiri hills where the Eastern and Western Ghats meet. The Cardomom Hills lying beyond may be regarded as a continuation of the western Ghats.