Geograph - photograph every grid square

The rocks here are layers of red sandstone dipping towards the south. As it follows the dip the Afon Giedd (a 'consequent' stream) occasionally crosses more resistant layers of sandstone and forms waterfalls at these points; this is the third marked on the 1:25000 O.S. map. The pool at the base of the fall is a 'plunge pool' and the whole waterfall is slowly retreating upstream, leaving behind a gorge (off to bottom right of photograph). On meeting the limestone further south the Afon Giedd mysteriously disappears underground at the base of a cliff.