<Li> The Bangar belt--consists of older alluvium and forms the alluvial terrace of the floodplains . In the Gangetic plains, it has a low upland covered by laterite deposits . </Li> <Li> The Khadar belt--lies in lowland areas after the Bangar belt . It is made up of fresh newer alluvium which is deposited by the rivers flowing down the plain . </Li> <P> The Indus - Ganga belt is the world's most extensive expanse of uninterrupted alluvium formed by the deposition of silt by the numerous rivers . The plains are flat and mostly treeless, making it conducive for irrigation through canals . The area is also rich in ground water sources. The plains are the world's most intensely farmed areas . The main crops grown are rice and wheat that are grown in rotation . Others include maize, sugarcane and cotton . The Indo - Gangetic plains rank among the world's most densely populated areas with a total population exceeding 400 million . </P> <P> Until recent history, the open grasslands of the Indus - Ganga Plain were inhabited by several large species of animal . The open plains were home to large numbers of herbivores which included all three of the Asian rhinoceros (Indian rhinoceros, Javan rhinoceros, Sumatran rhinoceros). The open grasslands were in many ways similar to the landscape of modern Africa . Gazelle, buffalo, rhinos, elephants, lions, and hippo roamed the grasslands as they do in Africa today . Large herds of Indian elephants, gazelles, antelopes and horses lived alongside several species of wild cattle including the now - extinct aurochs . In the forested areas there were several species of wild pig, deer and muntjac . In the wetter regions close to the Ganga, there would have been large herds of water buffalo grazing on the riverbanks along with extinct species of hippopotamus . </P>

Give two reasons why there are many large cities in the northern plains
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