These caves, which were first described by the present Bishop of Norwich in 1832, and have since been more fully explored by Dr cumming of Denbigh, were visited by the author in the autumn of 1837. The principal cave is a fissure in a grand mural escarpment of the mountain limestone of Wales, about two miles and a-half south-west of St Asaph, and occurs half-way down the precipice, which seems to be about 250 feet in height. It forms at that point the southern boundary of the limestone, which constitutes the basis of the Vale of Clwyd; and is divided from the extensive greywacke slate formation of that county by the narrow picturesque Vale of Cyffredin, through which the river Elwy flows.