Fold mountains are found in many parts of the world; they form along the plate
boundaries where great Earth movements have taken place.
There were long periods of quiet between Earth movements during which
sedimentary rocks, thousands of metres thick, formed in huge depressions called
Rivers carried sediments and deposited them into the depressions. Over millions
of years the sediments were compressed into sedimentary rocks such as sandstone
and limestone. These sedimentary rocks were then forced upwards into a series
of folds by the movement of the tectonic plates. Sometimes the folds were
simple upfolds (anticlines) and downfolds (synclines), as in the Jura mountains
in France. In some places the folds were pushed over on one side giving
overFolds, while in some of the highest fold mountains, like the Alps, the
rocks have been severely folded and faulted into nappes.
Fold mountains have been formed at times in the Earth's geological history
called mountain-building periods. Recent mountain-building movements have
created the Alps, the Himalayas, the Rockies and the Andes, some of which are
still rising. For this reason many of these ranges are called young fold