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In the conclusions of the paper it was suggested that similar folds were formed from curved surfaces that were either in existence within the rock before the plastic deformation or that might have been developed by flexure-folding of competent beds. Perfect similar folds would, however, only be developed if these curved surfaces already possessed a ‘similar’ shape. Structures made from flexure-folds could never have a perfect similar’ geometry and it should always be possible to detect flexure components in any fold by making measurements of thickness of individual beds in a direction parallel to the axial plane of the fold ; these measurements would always show a maximum value on the fold limbs and a minimum value at the fold hinges, no matter how intense the modification by homo-geneous plastic change of shape. The speaker had found that when such measurements were made on naturally occurring folds of similar type a very different geometry was discernible, and that either a maximum or a minimum value occurred on the fold hinges. This suggested that folds might be produced by inhomogeneous plastic deformation, a mechanism that must produce a component of de-formation by simple shear. At any point within a fold of similar type the total deformation was a
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This 250-word extract was created in the absence of an abstract.
