Earth Movements and the Major Landforms

The face of the earth is constantly being reshaped by the agents of denudation - running water, rain, frost, sun, wind, glaciers and waves, so that our present landforms are very varied and diverse. But these agents only modify the pattern of mountains, plateaux and pains which have been modelled by movements of the earth's crust.

Since the dawn of geological time, no less than nine orogenic or mountain building movements have taken place, folding and fracturing the earth's crust. Some of them occurred in Pre-Cambrian times 600-3500 million years ago. The three more recent orogenics are the Caledonian, Hercynian and
Alpine. The Caledonian, about 320 years ago raised the mountains of Scandinavia and Scotland, and is represented in North America. These ancient mountains have been worn down and no longer exhibit the striking forms that they must once have had. In a later period, during the Hercynian earth movements about 240 million years ago, such ranges as the Ural Mountains, the Pennines and Welsh Highs Highlands in Britain, the Harz Mountains in Germany, the Appalachians in America as well as the high plateaux of Siberia and China were formed. These mountains have also been reduced in size by the various sculpturing forces.
We are now living in an era very close to the last of major orogenic movements of the earth, the Alpine about 30 million years ago. Young fold mountain ranges were buckled up and overthrust on a gigantic scale. Being the most recently formed, these ranges, such as Alps, Himalayas, Andes and Rockies, are the loftiest and the most imposing. Their peaks are sometimes several kilometres high. But the time will come when these lofty ranges will be lowered like those that existed before them. From the eroded materials, new rocks will be formed, to be uplifted later to form the next generation of mountains.