AbstractNew road cuttings have exposed a large part of the Merioneth Series. The rocks are low‐grade thinly layered metasediments which have undergone extensive buckling resulting in tectonic ripples, mullions, and crenulations. It is suggested that the periclinal form of these structures may be the result of buckling layered sequences with longitudinal and transverse zones of constraint (heterogeneities). The process is analogous to ‘quilting’ of thin metal sheets and the heterogeneities are perhaps due to layer thickness variation. There are two foliations; which may form a progressive sequence of cleavage development during the evolution of the fold