Mountain Belts of the World Orogenesis or the formation of mountain ranges is one of the key means by which the continental crust maintains its average elevation, relief, and aerial extent. From the earliest history of its development, Earth's surface has apparently been characterized by mountain ranges. It has become clear that mountains go through long cycles, during which they are uplifted, then gradually waste by erosion, and finally cease to exist in the traditional sense of the word. Their former presence is recorded in the eroded remnants of gigantic batholiths and belts of highly deformed metamorphic rocks. Perhaps all continental rocks were parts of mountains at one time or another.
Mountains differ is age, history, origin, and size.
About the only think mountains have in common is the fact that they are higher than the surrounding terrain. There are certain characteristics of mountain groups which are of importance in understanding the process of orogenesis. Mountains are characterized by a hinterland and a foreland. The most severe deformation occurs where continent-continent collision has taken place. When a group of mountains which are so aligned are clearly related with respect to composition and origin, they constitute a mountain range or system .