In this illustrated lecture, the more prominent phases of the geological history of Ireland were pointed out, mainly as an explanation of the existing scenic features of the country. Probably very little remains in Ireland of the old Huronian continent, unless portions of it have appeared again in the cores of Caledonian folds. The stratified, but metamorphosed, Dalradians of the west may be Cambrian, or older; and gneiss is included in the granite of eastern Tyrone, the latter being probably of Caledonian age. The gneiss of the ancient moorland between Omagh and Cookstown is, moreover, very possibly pre-Cambrian. The Silurian sea must have covered all the Irish area ; and the subsequent Caledonian folding, with its axes running north-east and south-west, marked out the first distinct lines of the existing country.