The image is of the plunge pool of Thornton Force, Ingleton a classical example of a geological unconformity. In this example Carboniferous limestone rests on eroded Ordovician slates, once a wave-cut beach. An unconformity separates two rock masses of different ages and clearly indicates that sediment deposition was not continuous. Normally the rocks above an unconformity are younger than the lower rocks but geological strata, unlike archaeological ones, can be overturned. Ordovician slates are also found at White Scar Cave and there is a small exposure near Malham Tarn. These are the oldest Yorkshire rocks and as a general rule Yorkshire geology gets younger as you move east.