An anticline is also called an antiform and is a convex-up fold, where the limbs are the sides of the fold that dip away from the hinge. The oldest beds are in the centre, and the youngest beds are on the outside. Secondary anticlinal folds can develop and be superimposed on large anticlines and this type of feature is called an anticlinorium. In cross-section, secondary folds are fan-shaped. Anticlines and synclines are the basic components of folds. There are many types of anticlines: (1) linear anticlines (linear folds), which tend to form in active compressional orogenic belts; (2) dome anticlines, which form in stable platform areas; and (3) box anticlines and comb anticlines, which are typical features of anticlinal folds in transitional regions. Studies of anticlines can help to determine the mechanism and environment of folding. In a practical sense, anticlines are the main type of structure containing oil and gas, and they are the main targets for oil and gas exploration.