The rocks of the Parys Mountain, which lies about two miles to the south of the town of Amlwch in Anglesey, were described in 1878 by the late Mr. T. Fanning Evans, H.M. Inspector of Mines, who regarded the Parys Mountain “as an outlying piece of ground, geologically identical with the region in which the great slate-mines of Festiniog occur, and from which it differs only in being developed on a much smaller scale, and in being highly metalliferous.”