The Fold Mountains of the world have been formed by the contraction or displacement of crustal layers. All this could have been possible on account of the play of compressional and upthrust forces.
Metamorphic and igneous rocks are found below the layers of sedimentary rocks. The cores of the mountains are mainly composed of metamorphic rocks. The cause of the origin and development of metamorphic rocks is the excessive heat and pressure combination, which produced movement and forces the igneous rocks from the interior of the earth to the surface. Many mineral ores are also ejected along with the magma.
The Jura Mountains. The best examples of folded mountains in the world are illustrated by the Jura Mountain. It is composed of a series of sedimentary rocks. The marine fossils are also found in them. The Jura was once composed of horizontal sedimentary layers but later on folds were formed in the layers due to endogenetic forces. Now the mountains appear in an order of synclines and anticlines, which are alternatively formed. These mountains have fissures like any other folded mountain. These mountains have undergone erosion. The tops of anticlines have been eroded away and are scattered in the floors of the valleys. These mountains are in a youthful stage.
The Appalachian Mountains. One is wonder struck to see the tops of the Appalachian mountains in North America because the mountain tops are not anticline but syncline. When folded mountain tops are formed the tops of the mountains are always anticlines and the valleys synclines. Due to high pressure of the upthrusting force the anticlines develop cracks and fissures. This hastens the erosional activities. The valleys have few cracks and remain protected from the effect of winds. Hence, the valleys are less subjected to erosion. Due to greater erosion on the tops than in the valleys, the tops of mountains are eroded down to the level of valleys and a peneplain is formed.
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