含有泥质的碳酸盐胶体沉淀形成的灰岩，由于不同的矿物风化程度不同，较难风化的泥质呈眼球状凸现在岩石表面，故称“眼球状灰岩”，是二叠系栖霞组顶部的标志。The limestone was formed by sedimentation of mud-containing carbonate colloid. Different mineral compositions caused differential weathering, and the mud nodules that are more difficult to erode protrude from the rock surface, so the rock is called nodular limestone. It is the symbol of the top of Permian Qixia Formation.