FLEUTY'S CLASSIFICATION FOLD HINGE
PLUNGE AXIAL PLANE DIP
Depending upon the dip of the axial surface and plunge of the fold hinge, Fleuty (1964) classified the folds into a whole range of orientational forms from perfectly upright on one end to perfectly vertical on
the other and from perfectly upright to perfectly recumbent and from perfectly upright through numerous plunging inclined to reclined orientations to perfectly vertical. His classification in shown by means of a right angled triangle in the fig. A perfectly upright fold with a vertical axial plane and horizontal hinge may be rotated about an axis parallel to the hinge line to give rise to progressively slightly asymmetrical, highly asymmetrical, overturned and finally perfect recumbent structures with perfectly horizontal axial places (abscissa in fig). In this case the axial plane is allowed to rotate and assume lesser and lesser dips about the hinge line as the axis of rotation. In the second case of rotation, a perfectly upright fold with vertical axial plane and horizontal hinge line, the axial plane itself rotates, yet remaining vertical about a pole to it so that fold becomes progressively gently plunging, moderately plunging and steeply plunging and finally the fold hinge assumes complete verticality, the axial plane also remaining vertical to give rise to a vertical fold (ordinate in fig.). A vertical fold on rotation about a line which is the pole to axial plane will progressively give rise to steeply plunging, moderately plunging, gently plunging and finally recumbent structures (hypotenuse of triangle in fig). Thus Fleuty's diagram, although it takes only two entities into consideration, i.e. the fold hinge plunge and dip of axial plane is in fact a triangular diagram which encompasses almost all kinds of fold orientations. Diagonally across the diagram an upright fold may rotate about the point of intersection of the fold hinge and fold profile in such a manner that both the plunge of the hinge line and dip of the axial plane change and we get gently moderately and steeply inclined and finally reclined folds (from the right angle towards hypotenuse in figure).
