Fold mountains are caused by the pressure of two plates compressing upwards and downwards to create mountain ranges such as the Himalayas. There are also layers of folded sediments like the Jura or rock such at the Alps. The part which goes down is called a geosyncline while sediments as they are lighter go upwards to form the mountains.
The image above was taken during a flight from Spain to Switzerland. Below you can see the Alps covered in snow.