Returning to the British Isles we find that in the south the land was above its present level throughout the whole of the post-glacial period. On the other hand, a 25-foot beach is found in north-west England (Formby and Leasowe marine beds), but without any evidence as to climate; the same applies to the 25-foot beach of Scotland. It is only when we come to the north-east of Ireland that we find evidence of conditions appreciably warmer than the present, in the section of the Alexandra Dock, Belfast, where marine clays overlie beds of grey sand and peat. The lower estuarine clay is essentially a littoral clay, known as the _Scrobicularia_ zone. It is brownish-blue and sandy, and contains in abundance the roots and leaves of the grass-wrack (_Zostera marina_), and a vast number of shells of a few species which live between tide-marks, indicating that the land stood 10 feet or so above its present level at first, while the climate cannot have differed greatly from that prevailing at the present day. It must have been formed during a period of gradual depression, for throughout its six feet or more of thickness it preserves identical littoral characters. After a time this depression became more rapid, and the upper estuarine clay began to form—a light blue clay, very pure and unctuous, with a very rich and well-preserved fauna, known as the _Thracia_ zone. The fauna has a decidedly southern aspect, and indicates that the coasts of north-east Ireland had the present temperature of Bantry Bay—an increase of at least 3° F. in the mean annual temperature. The _Thracia_ zone is followed by a bed of yellow shore sand, indicating re-elevation to about seven feet above the present level. Corresponding to the upper estuarine clay are raised beaches at a height of 25 feet in north-east Ireland, falling to 15 feet at Dublin, and to only 6 or 7 feet in western Donegal and Sligo. The mollusca indicate a somewhat higher temperature than the present. In the beaches have been found flint scrapers and arrowheads of early Neolithic type. Looking further westwards, we find that Iceland, which had undergone a slight elevation during the continental phase, so that peat was formed below present sea-level, again subsided, falling to 10 or 12 feet below its present level. During this subsidence the temperature rose, the greatest warmth coinciding with the lowest level of the land. Species from the south-west shores, where the temperature of the water is directly influenced by the Gulf Drift, extended to the cold northern coast. In some places the marine clays of this period have been ploughed up by a subsequent readvance of the glaciers.