If an anomalous thick competent layer is present in an otherwise uniformly bedded sequence, chevron folds may show bulbous hinge zones, limb faults or thrusts (B in Figure second below) or curved limbs. On the other hand if an anomalous thin layer is present it may develop extension cracks, boudinage or alternatively the layer could get thinned ( A in Figure below)  under ductile deformation. It is the competent layers that control the dominant limb dip in the system. The shape changes in 

It is the competent layers that control the dominant limb dip in the system. The shape changes in competent layers could be adjusted if sufficient incompetent material is available. The ratio t1/t2 is most significant in this respect where t1 is the competent layer thickness and t2 is the incompetent layer thickness. Saddle reef structures (C in Fig) are usually developed in the hinge areas of incompetent layers, essentially due to dilation. If t1/t2 is high then the amount of incompetent material available for space filling is insufficient, dilation spaces are therefore large (C in figure). If t1/t2 is low, the amount of incompetent material available for space filling is large so that the dilation spaces are insignificant (D in Figure). Sometimes hinge collapse areas are produced due to change in incompetent as well as competent layer thickness.