Between the mountains of North Wales and the sea, occur two terraces, an upper composed of Boulder-day sloping towards the sea, and a lower, consisting of peat and alluvium, but little removed above high-water mark, running far inland, wherebroad valleys like the Vale of Clwyd breach the coast, and where rocky headlands jut into the sea, as the Great and LittleOrmes Heads. The two terraces are almost entirely denuded away, but often the lower one has alone suffered, as between Penmaen Bach and Penmaen Mawr, where a bay in the rocks, so to speak, is filled up with Upper Boulder-clay. It is quite evident that before denudation of the coast took place, the peat plain had a far greater extension than at present, which is proved by the foot of the occurrence of peat and a submarine forest at Rhyl, in borings in the Dee, and around the whole coasts of Cheshire, Lancashire, and southern Cumberland. It is also evident that considerable denudation of Glacial beds had taken place before the period of the old forests, and that the sea-ward prolongations of these beds, which themselves rested on an old sea-bottom, had been denuded away, and that a great plain, or series of plains, formed much of what is now the Irish Sea, before the forests came into existence; the lower terrace now fringing the coasts being the landward edge of this plain. It is nowhere better seen than in the Birket plain, forming the northern portion of the Hundred of Wirral, in North Cheshire. It is bounded to the south by an old pre-Glacial cliff, which abruptly terminates the northerly prolongation of all the numerous longitudinal valleys running with the strike of the Triassic rocks, of which this district is composed, each valley having a steep escarpment facing the west, as described by Professor Hull and myself.