ASYMMETRICAL FOLD

A fold whose limbs are unequal in length, and axial plane is inclined, dipping in the same direction as that of the gently dipping limb. Degree of asymmetry is given as the ratio of length of short to that of long limb. Thus, the smaller the ratio, greater is the degree of asymmetry. Folds whose axial plane is rotated clockwise from the normal to their enveloping surfaces are termed Z folds or dextral or negative asymmetrical while those in which the axial plane is rotated anticlockwise from the normal to their enveloping surfaces are termed S folds or sinistral or positive asymmetrical. Z and S folds normally occur on the left and right limbs of an antiform respectively. The photograph is of Z folds from the Ghisauli gneisses of Central India.