Out

on

a lim

b!

with thanks to Alan Richardson

Halesowen College

Pete Loader

WJEC Update

Symmetric

SymmetricAsymmetric

Asymmetric

What is the Fold Symmetry?

Limbs same dip

Limbs different dips

To quote a well known source:

Not a lot ofpeople know

that!

Symmetrical folds

• There exists a common misconception that the dips of limbs of a symmetrical fold must have equal dips in opposite directions. This need not be the case, but the lengths of the limbs must be equal.

• In a symmetric fold the enveloping surface (the surface describing the average dip of a folded bed) is at right angles to the axial surface.RJ Lisle – Geological Structures and Maps

• WJEC will accept this definition in the new spec. so will indicate the length of the limbs in questions.