Harmonic Folds

Harmonically folded multilayers in alternating marble and calc-silicate layers. The competent calc-silicate layers stand above the overall level of the outcrop surface because they are more resistant erosion and form class 1B or 1C folds, whereas the less competent marble layers form class 3 folds. The layers are considered to be harmonically folded because all share the same axial surfaces (blue), which are not necessarily planar. Photo credit: John Ramsay.