Severa years ago I deduced from the distribution of the mammalian cave-fauna of Ireland that an unknown extent of Older Drift existed in the southern part of that country and that the end-moraine of the Newer Drift, bordering it on the north, ran somewhere to the south of the Central Plain. During a series of excursions into the Dublin and Wicklow Hills in the company of Mr. A. W. Stelfox, of the National Museum, Dublin, this moraine was readily detected skirting their flanks; subsequent researches led to its complete mapping from coast to coast.