Referred to collectively as the Longmyndian Supergroup, the rock sequence is divided into two groups; the older Stretton Group comprising five named formations and the younger Wentnor Group formed of two formations. The entire 7000m thick succession was folded into an NE-SW aligned syncline, the Long Mynd Syncline. The axis of the syncline lies to the west of Long Mynd itself.

The 180m thick sequence of mudstones,