Folded rock strata. Rock strata folded up into a pointed shape or anticline. The rock at the base of the anticline has been eroded away to form a cave. These strata were formed from horizontal layers of sediment which became compressed into rock whilst deep underground. The rock became folded in this way because of the huge forces generated when the plates in the Earth's crust move against each other. Photograph of the Lady Cave in Saundersfoot, Great Britain.