Geology for the
Fold, in geology, means a bent or deformed arrangement of
stratified (layered) rocks.
These rocks may be of sedimentary or volcanic origin.
Although stratified rocks are normally deposited on the earth's surface
in horizontal layers, they are often found inclined or curved upward or
Arches, or upfolds, in stratified rock are called
Depressions or downfolds are called synclines.
Folds are commonly formed at some distance below the
surface, but complete folds or portions of folds are exposed by erosion.
Anticlines frequently have their crests eroded, till only
the worn-down stumps of the two limbs remain.
In a similar manner synclines may be eroded so that only the
edges of the limbs project above the surface.
The immediate cause of folding is generally conceded to be
the horizontal compression of the earth's surface, anticlines being
squeezed up by this compression and synclines formed between anticlines.
Porous and permeable rocks of anticlines often contain oil
and gas reservoirs.