An Encyclopaedia of Indian Archaeology v1.c14.s10.t1: 9.10.1 Pleistocene
An Encyclopaedia of Indian Archaeology v1.c14.s10.t1
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9.10.1 Pleistocene
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River valleys are the most common and important land-forms in every country. They come into existence as soon as the water on the land begins to flow over the uneven natural surface. Further developments in river valleys take place by the erosion of the bed-rock and the deposition of the sediments thus formed. As each stream carves its own valley several streams in the drainage network form several valleys which coalesce with each other and the resulting landscape presents a topography of hills and valleys. Normally each river valley passes through three stages—young, mature and old—from the source of the river to its end in the sea, lake-basin or some other river. The valleys are deep, gorge-like in the mountainous tract, V-shaped at the lower altitudes, broad and shallow on the plains and deltaic near the sea coasts. Depending on climate, underlying geological foundation and differential erosion of rocks, the stage in the cycle of river life, etc., they develop straight, braided or meandering courses.
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In India some rivers have perennial water like the Himalayan rivers which are fed by the melting water of glaciers as well as water received during the monsoon. The Narmada, Tapti, Godavari, Krishna, etc., of peninsular India swell during the rainy season but the quantity of water dwindles during other seasons. The majority of small rivers however carry water only during the monsoon but dry out later very rapidly.
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Rivers have provided a suitable environment for human settlement at all times—from the prehistoric period down to the present day. In the prehistoric times man being a hunter and food-gatherer obtained most of the requirements for his sustenance in the river valleys which bore thick natural vegetation and wild animal life. Later on, when animals were domesticated and the cultivation of crops was initiated, man continued to occupy this land-form as it provided natural fertile soils on the river flood plains for raising crops. Thus numerous Stone Age sites have been discovered in the valleys of the Ganga, NARMADA, TAPTI, GODAVARI, Sabarmati, etc., and their numerous tributaries. Rivers have yet another advantage in that they provide an easy communication for movement for trade, invasion, etc., and it can be seen that important trade routes of ancient times are located in the river valleys.
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Every river is prone to change its course, and this is brought about by differential erosion of the bed-rock, climatic changes and eustatic and tectonic effects. Waterfalls, meanders, ox-bow lakes, river terraces, etc., are some of the most conspicuous land-forms thus created. The more powerful down-cutting streams in the mountainous tract often capture (river piracy) water of the less powerful adjacent streams and the valley of beheaded streams is often dry.
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The TAPTI, NARMADA and Ganga-Yamuna are examples of tectonic valleys (rift valleys) which were the areas of excessive sedimentation during the Quaternary and have preserved a more or less continuous stratigraphic record of the prehistoric past in the form of Stone Age artefacts and fossils of contemporary animals.
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The Quaternary climatic changes [7.3] have been recorded in the Indian river valleys in the form of massive alluvial cones (the BANGANGA-BEAS valleys), morainic deposits (the LIDDAR near Pahlgam, Kashmir basin), lake deposits (*karewas* in Kashmir) and cut-and-fill valleys [9.9] in the peninsular area, and with all of these river valleys are associated human settlements of different periods.
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For river valleys see respective entries in vol. II.—R.V. JOSHI