Folds may be symmetrical or asymmetrical. In a symmetrical fold (image at left), the axial plane is vertical and the limbs (sides) dip symmetrically from the axis. In an asymmetrical fold, the axial plane is tilted from the vertical with one limb dipping more steeply than the other.
By convention, plunge direction is expressed as a three-digit number, and the plunge by a two-digit number. Thus, a line plunging 35º toward the azimuth 35º will be noted: 45º->035
Monoclinal folding drapes strata as though over a ledge, whereas hinge folding wraps the limbs of a fold as though hinged around the fold axis.
However, the apparent shape of a fold may be distorted by the angle of erosional exposure relative to the fold axis (image at left).
(Try this with a stick of celery.)
├ .. On geological maps, the stike and dip of bedding, rather than axes and folds, are indicated.
▪ faulting ▪ fault attributes – net-slip, dip-slip, dip vector, strike-slip, vertical-throw, horizontal-throw, horizontal vector, heave, rake