Folding / Складки

The previous chapter dealt with planar geological surfaces. A geological surface which is curved is said to be folded. Most folding is the result of crustal deformation whereby rock layering such as bedding has been subjected to a shortening in a direction within the layering. To demonstrate this place both hands on a tablecloth and draw them together; the shortening of the tablecloth results in a number of folds.

The structure known as folding is not everywhere developed equally. For example the Upper Carboniferous rocks of southwestern England and southernmost Wales show intense folding when compared to rocks of the same age further north in Britain. The crustal deformation responsible for the production of this folding was clearly more severe in certain areas. Zones of concentrated deformation and folding are called fold belts or mountain belts, and these occupy long parallel-sided tracts of the earth’s crust. For example, the present-day mountain chain of the Andes is a fold belt produced by the shortening of the rocks of South America since the end of the Cretaceous times. <...>