 The upper band is made up of whinstone, or dolerite, a hard igneous rock which the waterfall takes a lot of time to erode.The lower section is made up of Carboniferous Limestone, a softer rock which is more easily worn away by the waterfall.Between these two layers is a thinner layer of Carboniferous sandstone, which was baked hard when the Whin Sill was molten 295 million years ago.