And now, just as a point is reached when at length we think we shall see our present British flora emerging fully from the obscurity of the ages, a dramatic interruption occurs, which confuses the record and brings us into difficulties of many sorts, giving rise to controversies which are still far from being settled. The climate becomes suddenly colder, and Europe is plunged into the rigours of the Ice Age. Ice Ages there had been before in the long history of the world. Rocks of late Permian or early Carboniferous times bear ample witness to the existence of great ice sheets extending over wide areas in several continents where temperate or warm conditions now prevail: and puzzling deposits of later age--Cretaceous, Eocene, Miocene--have been interpreted by some geologists as the relics of subsequent Glacial Periods. But these are only distant echoes as compared with the Quaternary Ice Age, from the effects of which our country and its fauna and flora are still in process of recovery. At the close of the Pliocene Period, then, snow began to extend on the higher grounds, and glaciers to fill the mountain valleys; these conditions were intensified until all Northern Europe, including the British Isles as far south as the Thames valley, lay under a mantle of ice. The plants which occupied the ground were forced southward as the ice advanced, or exterminated by the increasing cold. After long fluctuations of climate, the extent of which appears still in doubt, the ice at length slowly passed away, leaving the surface of our country greatly altered. The ancient soils which had been in process of accumulation since last the land rose above sea-level were swept away, the surface was strewn with materials formed by the grinding down of the hills or the pushing up of sea-bottom material, valleys were choked, rivers diverted, lakes formed by dams of glacial detritus, or by the scooping action of the ice; the whole surface of the country was remodelled on new lines. Into this new land the plants remigrated, and we now view on our hills and plains the results of this repopulation. The difficulties of which I have spoken arise especially in connection with the manner of this recolonization. On a continental area one can conceive of a gradual retirement of the flora before the advance of the ice, and its subsequent remigration northward into its old haunts as the ice retired. But on an insular area like Great Britain no such line of retreat was open. The ice-free area of Southern England and possibly Southern Ireland does not appear adequate to harbour the crowd of refugees throughout the cold period. There is good evidence that the time of maximum glaciation was also one of elevation of the land, and possibly this persisted for a while after the passing away of the ice. If this were so, some relief from the congestion might have been afforded to the refugees during the cold period, and an opportunity