Old fold mountains :
The fold mountains which were formed about more than 250 million years ago are called old fold mountains. For example, the Urals in Russia, the Appalachians in North America and the Aravalli range in India are old fold mountains. These mountain ranges are of low altitude and have gentle slopes.
Young fold mountains :
The most recent phase of mountain building took place about 25 million years ago. The world’s highest mountain ranges were formed during this period. These are known as young fold mountains. They have rugged relief features because they have been subjected to denudation for a comparatively short period only.
