In a single layer of an anticline, the dip isogons converge towards the inner surface (core). Which one of the following statements is correct for the curvature of the inner surface of this folded layer?
IIT JAM - 2026,
Answer: A
The inner surface has the greater curvature: curvature of the inner surface > curvature of the outer surface.
Dip isogons join points of equal dip on the two surfaces of a folded layer. In Ramsay's classification, isogons converging towards the core define Class 1 folds, in which the outer arc is more gently curved than the inner arc. In Class 1B, the parallel fold, the layer keeps a constant thickness, so the inner arc has the smaller radius and therefore the larger curvature; Classes 1A and 1C show the same inequality.
Equal curvature on both surfaces describes Class 2, the similar fold, whose isogons are parallel. A greater curvature on the outer surface describes Class 3, whose isogons diverge towards the core. The median surface is not what the question compares.
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