A body of water falling down from a mountain rock is known as a ‘waterfall’. If water falls from a great height in the form of a large stream, it is called a ‘cataract’. But, if the falling stream is narrow, it is called a ‘cascade’. It is essential for the formation of a waterfall that water flows through certain hard rocky areas. Hard rocks should be followed by soft soil which water can easily cut through. At some places, due to natural changes, the river flows through areas, which are higher than the sea level and thus water falls from a height. Sometimes, flow of the river is obstructed by landslides. Water accumulates there and later, falls down in the form of a waterfall. There are many kinds of waterfalls at many hilly places. The Angel waterfall of Venezuela in South America, is the highest waterfall of the world. Here water falls from a height of 978 metres. This was discovered, in 1835, by Jimmy Angel, a pilot in the U.S. Air Force. The highest waterfall of Asia is the Gersoppa waterfall, in India. The Niagara waterfall is also world-famous for many reasons. Situated 25 kilometres north-west of New York in the U.S.A., this waterfall of Niagara River is divided into two parts. One part is in the possession of the U.S.A., while the other is in possession of Canada. This waterfall actually, acts as the international boundary between these two countries. The Ribbon waterfall of California in America is the highest narrow-stream waterfall of the world. A narrow stream, falls into the Merced River from a height of 490 metres. The widest waterfall of the world is the Khoni waterfall having a width of 11 kilometres. Some waterfalls have proved very useful to man. Hydroelectricity, produced from waterfalls, is used for innumerable purposes.