Geologists are still discovering the extent to which the rocks of the earth are mobile. Movements that take place within the earth generate stresses which can be capable of deforming rocks, that is, changing their overall shape. This deformation can occur in a brittle way, where the rocks change shape by fracturing, or in a ductile way. In the latter case, because of factors that come about at depth in the earth, such as increased pressure and temperature and longer times of deformation, the rocks respond to any stress by flow, and there is no fracture. The common way in which bedded sedimentary rocks deform in a ductile way is by warping into the wave-like shapes known as folds.
KeywordsFold Axis Axial Surface Hinge Zone Namurian Series Axial Trace
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