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376
GEOLOGY
INDIA


still farther south, furnish the gateways between India and Afghanistan.The Hala, Brahui and Pab mountains, forming the southern hilly offshoots between India and Baluchistan, have a much less elevation.

The wide plains watered by the Himalayan rivers form the second of the three regions into which we have divided India. They extend River plains. from the Bay of Bengal on the east to the Afghan frontier and the Arabian Sea on the west, and contain the richest and most densely crowded provinces of the empire. One set of invaders after another has from prehistoric times entered by the passes at their eastern and north-western frontiers. They followed the courses of the rivers, and pushed the earlier comers southwards before them towards the sea. About 167 millions of people now live on and around these river plains, in the provinces known as the lieutenant-governorship of Bengal, Eastern Bengal and Assam, the United Provinces, the Punjab, Sind, Rajputana and other native states.

The vast level tract which thus covers northern India is watered by three distinct river systems. One of these systems takes its rise River systems. in the hollow trough beyond the Himalayas, and issues through their western ranges upon the Punjab as the Sutlej and Indus. The second of the three river systems also takes its rise beyond the double wall of the Himalayas, not very far from the sources of the Indus and the Sutlej. It turns, however, almost due east instead of west, enters India at the eastern extremity of the Himalayas, and becomes the Brahmaputra of Eastern Bengal and Assam. These rivers collect the drainage of the northern slopes of the Himalayas, and convey it, by long and tortuous although opposite routes, into India. Indeed, the special feature of the Himalayas is that they send down the rainfall from their northern as well as from their southern slopes to the Indian plains. The third river system of northern India receives the drainage of their southern slopes, and eventually unites into the mighty stream of the Ganges. In this way the rainfall, alike from the northern and southern slopes of the Himalayas, pours down into the river plains of Bengal.

The third division of India comprises the three-sided table-land which covers the southern half or more strictly peninsular portion Northern table-land. of India. This tract, known in ancient times as the Deccan (Dakshin), literally “the right hand or south,” comprises the Central Provinces and Berar, the presidencies of Madras and Bombay, and the territories of Hyderabad, Mysore and other feudatory states. It had in 1901 an aggregate population of about 100 millions.

The northern side rests on confused ranges, running with a general direction of east to west, and known in the aggregate as the Vindhya mountains. The Vindhyas, however, are made up of several distinct hill systems. Two sacred peaks guard the flanks in the extreme east and west, with a succession of ranges stretching 800 m. between. At the western extremity, Mount Abu, famous for its exquisite Jain temples, rises, as a solitary outpost of the Aravalli hills 5650 ft. above the Rajputana plain, like an island out of the sea. On the extreme east, Mount Parasnath—like Mount Abu on the extreme west, sacred to Jain rites—rises to 4400 ft. above the level of the Gangetic plains. The various ranges of the Vindhyas, from 1500 to over 4000 ft. high, form, as it were, the northern wall and buttresses which support the central table-land. Though now pierced by road and railway, they stood in former times as a barrier of mountain and jungle between northern and southern India, and formed one of the main obstructions to welding the whole into an empire. They consist of vast masses of forests, ridges and peaks, broken by cultivated valleys and broad high-lying plains.

The other two sides of the elevated southern triangle are known as the Eastern and Western Ghats. These start southwards from Ghats. the eastern and western extremities of the Vindhya system, and run along the eastern and western coasts of India. The Eastern Ghats stretch in fragmentary spurs and ranges down the Madras presidency, here and there receding inland and leaving broad level tracts between their base and the coast. The Western Ghats form the great sea-wall of the Bombay presidency, with only a narrow strip between them and the shore. In many parts they rise in magnificent precipices and headlands out of the ocean, and truly look like colossal “passes or landing-stairs” (gháts) from the sea. The Eastern Ghats have an average elevation of 1500 ft. The Western Ghats ascend more abruptly from the sea to an average height of about 3000 ft. with peaks up to 4700, along the Bombay coast, rising to 7000 and even 8760 in the upheaved angle which they unite to form with the Eastern Ghats, towards their southern extremity.

The inner triangular plateau thus enclosed lies from 1000 to 3000 ft. above the level of the sea. But it is dotted with peaks and seamed with ranges exceeding 4000 ft. in height. Its best known hills are the Nilgiris, with the summer capital of Madras, Ootacamund, 7000 ft. above the sea. The highest point is Dodabetta Peak (8760 ft.), at the upheaved southern angle.

On the eastern side of India, the Ghats form a series of spurs and buttresses for the elevated inner plateau, rather than a continuous Eastern Ghats. mountain wall. They are traversed by a number of broad and easy passages from the Madras coast. Through these openings the rainfall of the southern half of the inner plateau reaches the sea. The drainage from the northern or Vindhyan edge of the three-sided table-land falls into the Ganges. The Nerbudda and Tapti carry the rainfall of the southern slopes of the Vindhyas and of the Satpura hills, in almost parallel lines, into the Gulf of Cambay. But from Surat, in 21° 9′, to Cape Comorin, in 8° 4′, no large river succeeds in reaching the western coast from the interior table-land. The Western Ghats form, in fact, a lofty unbroken barrier between the waters of the central plateau and the Indian Ocean. The drainage has therefore to make its way across India to the eastwards, now turning sharply round projecting ranges, now tumbling down ravines, or rushing along the valleys, until the rain which the Bombay sea-breeze has dropped upon the Western Ghats finally falls into the Bay of Bengal. In this way the three great rivers of the Madras Presidency, viz., the Godavari, the Kistna and the Cauvery, rise in the mountains overhanging the western coast, and traverse the whole breadth of the central table-land before they reach the sea on the eastern shores of India.

Of the three regions of India thus briefly surveyed, the first, or the Himalayas, lies for the most part beyond the British frontier, but a knowledge of it supplies the key to the ethnology and history of India. The second region, or the great river plains in the north, formed the theatre of the ancient race-movements which shaped the civilization and the political destinies of the whole Indian peninsula. The third region, or the triangular table-land in the south, has a character quite distinct from either of the other two divisions, and a population which is now working out a separate development of its own. Broadly speaking, the Himalayas are peopled by Mongoloid tribes; the great river plains of Hindustan are still the home of the Aryan race; the triangular table-land has formed an arena for a long struggle between that gifted race from the north and what is known as the Dravidian stock in the south.

Geology.

Geologically, as well as physically, India consists of three distinct regions, the Himalayas, the Peninsula, and—between these two—the Indo-Gangetic plain with its covering of alluvium and wind-blown sands. The contrast between the Himalayas and the Peninsula is one of fundamental importance. The former, from the Tertiary period even to the present day, has been a region of compression; the latter, since the Carboniferous period at least, has been a region of equilibrium or of tension. In the former even the Pliocene beds are crumpled and folded, over folded and over thrust in the most violent fashion; in the latter none but the oldest beds, certainly none so late as the Permian, have been crumpled or crushed—occasionally they are bent and frequently they are faulted, but the faults, though sometimes of considerable magnitude, are simple dislocations, unaccompanied by any serious disturbance of the strata. The greater part of the Himalayan region lay beneath the sea from early Palaeozoic times to the Eocene period, and the deposits are accordingly marine; the Peninsula, on the other hand, has been land since the Permian period at least—there is, indeed, no evidence that it was ever beneath the sea—only on its margins are any marine deposits to be found. It should, however, be mentioned that in the eastern part of the Himalayas some of the beds resemble those of the Peninsula, and it appears that a part of the old Indian continent has here been involved in the folds of the mountain chain.

The geology of the Himalayas being described elsewhere (see Himalayas), the following account deals only with the Indo-Gangetic plain and the Peninsula.

The Indo-Gangetic Plain covers an area of about 300,000 sq. m., and varies in width from 90 to nearly 300 m. It rises very gradually from the sea at either end; the lowest point of the watershed between the Punjab rivers and the Ganges is about 924 ft. above the sea. This point, by a line measured down the valley, but not following the winding of the river, is about 1050 m. from the mouth of the Ganges and 850 m. from the mouth of the Indus, so that the average inclination of the plain, from the central watershed to the sea, is only about 1 ft. per mile. It is less near the sea, Where for long distances there is no fall at all. Near the watershed it is generally more; but there is here no ridge of high ground between the Indus and the Ganges, and a very trifling change of level would often turn the upper waters of one river into the other. It is not unlikely that such changes have in past time occurred; and if so an explanation is afforded of the occurrence of allied forms of freshwater dolphins (Platanista) and of many other animals in the two rivers and in the Brahmaputra.

The alluvial deposits of the plain, as made known by the boring at Calcutta, prove a gradual depression of the area in recent times. There are peat and forest beds, which must have grown quietly at the surface, alternating with deposits of gravel, sand and clay. The thickness of the delta deposit is unknown; 481 ft. was proved at the bore hole, but probably this represents only a small part of the deposit. Outside the delta, in the Bay of Bengal, is a deep depression known as the “swatch of no ground”; all around it the soundings are only of 5 to 10 fathoms, but they very rapidly deepen to over 300 fathoms. Mr J. Ferguson has shown that the sediment is carried away from this area by the set of the currents; probably then it has remained free from sediment whilst the neighbouring sea bottom has gradually been filled up. If so, the thickness of the alluvium is at least 1800 ft., and may be much more. At Lucknow