The Peninsula

The peninsular massif of India is made up of hard igneous and metamorphic rocks and generally has gentle gradients produced by prolonged weathering and erosion. Despite its vast expanse south of the Indo-Gangetic plain, ranges that exceed 1,000m in elevation are localised as residual plateaus. These are the Eastern and Western Ghats, Satpura-Maikal, Aravalli, and highlands of Sri Lanka.

The Eastern Ghats or uplands along the eastern side of Peninsular India have no structural or topographic continuity. Neither are they really ranges like the Western Ghats but rather uplifted plateaus separated by major basins. These have been recognised as being in four sections: (1) north of Mahanadi, (2) between Mahanadi and Krishna, (3) between Krishna and Penner, and (4) south of Penner converging to the Western Ghats. The northern section is formed of intrusive igneous rocks with a banded iron formation. The prominent ridges run north-south with heavily forested deep valleys. A few peaks are just over 1,000m. South of the Mahanadi, the Ghats run south parallel to the west coast. They comprise of metamorphosed sedimentaries giving rise to smooth, hummocky hills. In places, intrusive granites form rugged hills with surfaces covered with large blocks and tors. Their average elevation is 1,100m, the highest point being Mahendragiri (1,501m). The third section, the Nallamala Range, extends from Guntur to Cuddapah in an arcuate form with concavity to the east. Despite the low average elevation (760m), the range is rugged with jagged peaks and steep slopes. This is the home of the Chenchu, a primitive food gathering tribe. The fourth section, west of Madras, includes the Palkonda, Javadi, and Shevaroy hills. Mostly composed of charnockite massifs, they have steep sides with rolling topography on the top. North of the Cauvery River, the Shevaroy hills merge into the Nilgiri hills, a part of the Western Ghats.

Before turning to the Western Ghats, it seems logical to deal with the Sri Lankan highlands as they are a geological extension of the Peninsular system. This refers to the igneous intrusions of the Khondalite series of old gneisses and schists. The Central Highlands constitute a plateau of from 1,800-2,000m in elevation that extends over 70 km between the Hatton and Welimada peaks. The western section has a series of ridges, while the eastern section has gentle rounded forms with some deep gorges. Although their structure is complex, the highlands have two erosional surfaces, indicating successive uplift movements. The upper plateau or `up country' becomes dominant south-west of Kandy where the prominent peaks include the Pidurutalagala (2,524m), which is the highest on the island, and the spectacular Adam's Peak (2,243m). The highlands have been much eroded by rivers that drain out in a radial pattern, and some have waterfalls that have been used for hydropower. The highest zones receive heavy rain from the south-west monsoon and originally had dense forest. Natural vegetation has been largely cleared since the early 19th century for plantation of cash crops. The sequence of plantation crops here is an interesting instance of the varying effects of physical and economic factors. The first cash crop to be introduced was cinnamon, then followed coffee, cinchona, and finally tea; the latter being the principal crop today.

The Western Ghats, Sahyadri in Sanskrit, run for about 1,600 km along the western border of the Deccan from Cape Camorin to the River Tapti. Their average elevation is 1,200m. They are not true mountains but rather the faulted edge of an upraised plateau. There is a contrast between the deep ravines and canyons along the scarp facing the Arabian Sea and the flat-topped spurs intersected by mature valleys to the east. The three sections of the Western Ghats roughly correspond to their extensions in the states of Kerala, Karnatak, and Maharashtra. The southern section, on either side of the Palghat Gap (300m), has the highest ranges in the Peninsula. Anai Mudi (2,695m), the highest peak, is a nodal point from which three ranges radiate - the Anaimalai to the north, Palni to the north-east, and the Cardamom hills to the south. The last range, approaching closely the southern tip of India, is also called the Southern Ghats. The heavy rainfall, averaging 5,000m per annum is conducive to the growth of rich forests. The Palni hills are much more accentuated towards the west, rising to 2,506m. The hill station of Kodaikanal (2,195m) stands at the southern edge of the central part. The Anaimalai Range is a series of plateaus intersected by deep valleys. Its forests contain large timber trees such as teak, ebony, and rosewood. These southern hills support large coffee plantations. The Nilgiri (Blue Mountain), a compact plateau north of Palghat, is the point at which the Eastern and Western Ghats converge. The highest peak is the Dodda Betta (2,637m). Its rich vegetation has affinities to the humid flora of Assam. Plantation crops of tea and coffee dominate, while the tribal Toda tend buffaloes on the grasslands. Ootacamund in the Nilgiri hills is the leading holiday resort in south India.

The second section of the Western Ghats extends 650 km north from Gudalur to Belgaum. The rocks are mainly granitoid gneisses, and the range runs very close to the coast. The Jog Falls, with a sheer drop of 250m, are in this area as also the peak of Kudramukh (1,894m). Heavy rainfall favours dense forest growth. Much of this forest has been affected by shifting cultivation (kumri). The third section of the Western Ghats extends 650 km from 16° N latitude to the Chandor hills south of the Tapti. These are mainly composed of horizontal sheets of lava. They are 50 to 60 km from the coast and have an average elevation of 550m. Northwards, they show a monoclinal fold, the western limb of which dips gently towards the sea. Further south, the range steeply faces towards the coast and gently slopes eastwards. More important eminences include the Kalsubai (1,646m) in the Harishcandra Range and the Mahabaleswar (1,478m) which is on another range of the same name.

The Satpuras (Seven Folds) extend 900km east-west between the Tapti and Narmada rivers in central India. The western-most part, locally known as the Rajpipla hills, is a steep-sided Deccan lava block with a high craggy ridge. The more extensive central part has the Gawilgarh hills to the south and the Mahadeo hills to the north. The former is another Deccan lava horst and the latter is formed of Gondwana quartzite with precipitous scarps. The highest peak of the Satpuras, Dhupgarh (1,350m) near Pachmarhi hill station, lies in the Mahadeo hills. The eastern part of the Satpuras is known as the Maikal hills, crowned by the Amarkantak (1,065m). This plateau is tilted north-west and much dissected by streams draining into the Narmada. The upper slopes still carry forests that support lumbering and charcoal making. Shifting cultivation is practised by various Gond tribes who are also engaged as forest workers.

The Aravalli, the oldest mountain range in India, extends nearly 700km from Gujarat to Delhi. Its main south-west/north-east strike is remarkably regular, and it is marked by a central range of ancient gneisses and schists. The Aravalli Range culminates (1,315m) in the headwaters of the Sabarmati River near Udaipur. However, the highest point, Guru Sikhar (1,722m) on Mount Abu, lies off the main axis in the extreme south-west. The well-defined range near Udaipur, called the Mewar hills, presents a steep scarp on the western side. Then commence two ridges running parallel for 100 km, separating the Marwar (Region of Death) on the west and the Mewar on the east. Near Ajmer, they separate out into a number of jagged hills of quartzites. North of Jaipur, the range is marked by low ridges half-buried in the alluvium. On the frontier of the Thar desert, the land experiences frequent drought. The hill forests are xerophytic and degraded. The people on the west side are semi-nomadic and range widely to graze their cattle. In the comparatively more humid east, Bhil tribes practise shifting cultivation.