A History of Agriculture in India v1.c8.s1.3

v1.c8.s1.3

The aqueous agency operating in the disintegration of rocks and soils is the most potent of all. What enormous quantities of solid matter are dislocated by rain and brought down by streams and rivers may be judged from Everest's calculation of silt carried down by the Ganges alone. Everest has calculated that 355,361,461 tonnes of solid matter are carried down annually to the sea by the Ganges. The erosive action of running water is due to sand, pebbles and rocks carried by it. The hardest and heaviest rocks become converted into rounded boulders and pebbles by the action of the moving water containing sand in motion. Water acts not only mechanically in denuding rocks, but it is also a solvent. Potash, soda, silica and lime get dissolved in water, and the rocks are denuded by the solvent action Fig. 3. The occurrence of Archaean and Purana Rocks and the Deccan Trap in India of water. The solvent action of water and minerals is increased by salts in solution and gases in suspension. Sea waves beating against cliffs also help in the formation of soils. The action of glaciers in tearing down rocks and in the formation of moraines and erratic boulders may be also included under this head. The hydration of rocks in the presence of water may also be mentioned.