Bedding mullions have been produced by compression parallel to bedding in the hinge region of a large recumbent fold. Geometrically, the mullions are a combination of parasitic folding, with characteristic gadrooned profile, and cleavage planes. The cleavage is not an axial plane structure, but where fully developed produces a perfect slate fabric in rocks of appropriate lithology. The mullions are found on both sides of a bed of inferior slate sandwiched between two beds of good roofing slate. Boudinage structure results where the mullions are exactly back to back, and the planes of separation provided by the cleavage are infilled with coarse calcite. The slates are interbedded and interlaminated with limestone. Such boudins are unusual in that they occupy the hinge region of a fold and result from compression parallel, rather than at right angles, to the bedding.

You do not currently have access to this article.