The main types of folds are syncline and anticline, and the fold structure includes a curved shaft ridge and two wings. The axis of the fold is parallel to the axial ridge area and overlaps with the axial plane of this area. Geometrically, folds can be divided into the following types: parallel folds, similar folds, concentric folds, open folds, isometric folds and so on. In order to accurately determine the inclination angle of folds, it is necessary to measure the direction of axial ridges and axial planes of folds. Different axial ridges and axes will cause different inclination angles of this fold, such as vertical, inclined (horizontal and inclined), upright, horizontal and recumbent, which are all distinguished according to different inclination angles.
Although folds have changed the original occurrence of rocks, they have not lost their continuity and integrity.