Lakes represent another form of irregularity in the long profile of rivers in their early stages. The Himalayan Rivers have practically no lakes along their courses. This indicates the relative maturity of landscape in the region.
Now we take up the complicated question of the grading of long-profile. So long as a river flows from source to mouth at every point on the course, it tends to grade the channel.
Africa stands second only to Asia in size. It occupies 22 per cent of the earth’s land area and straddles the equator on both the north and south. Most of Africa is an ancient plateau of what made up the Gondwanaland.
Democratic Republic of Congo and Nigeria are two important equatorial countries of Africa. While the former is situated on both sides of the equator, Nigeria lies within the tropics with its southern half in the equatorial belt.
South America is the fourth largest continent with twelve per cent of the world’s landmass. A major portion of this continent lies in southern hemisphere. It has very high mountains, large plateaus and great river plains.
Argentina occupies the southern part of South America. It is the second largest South American country. The island of Tierra del Fuego lies at its southern tip separated from the mainland by the Magellan strait.