OROGENESIS

As mentioned earlier, orogenesis is the process by which mountains are formed. Orogenic movements result in the thrusting, folding and faulting that form the major mountain ranges. This occurs when two continents collide and the sediments between them are intensely deformed into linear mountain ranges. Volcanic activity and earthquakes are closely associated with orogenesis.
Since the dawn of geological time, no less than nine orogenic movements have taken place. Some of them occurred in Pre-Cambrian times between 600-3,500 million years ago. The three more recent orogenies are:

(i) The Caledonian About 320 million years ago, the Caledonian orogenies raised the mountains of Scandinavia and Scotland. This orogenies is represented in North America.
(ii) The Hercynian During the Hercynian earth move­ments, which occurred about 240 million years ago, ranges such as the Ural Mountains, the Pennines and Welsh Highlands in Britain, the Harz Mountains in Germany, the Appalachians in America were formed.
(iii) The Alpine The Alpine movement occurred 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 the Alps, the Himalayas, the Andes and the Rockies are the loftiest and the most imposing.