It seems that at the top of St. George's Down we are standing on what was once the floor of an old valley. In the course of denudation the bottom of a river valley often becomes the highest part of a district. For the bed of the valley is covered by flint gravel, and flint is excessively hard, and the bed of flints protects the underlying rock; so that, while the rocks on each side are worn away, what was the river bed is eventually left high above them. Thus the highest points of a district are often capped by flint gravel marking the beds of old streams. Tracing up this old valley to the southward, at a few miles distance it will have reached the chalk region on the south of the anticline: and the flints carried down the valley may have come from beds of angular flints already dissolved out of the chalk such as we find on St. Boniface Down. But how have these great masses of flints been swept along? Can the land have been down under the sea; and have sea waves washed the stones along? But these flints, though water-worn, are not rounded as we find beach shingle. What immense rush of water can have spread these flints 30 feet deep along a river valley? We must go to mountain regions for torrents of this character. And then, mountain torrents round the stones in their bed while these are mostly angular. The history of these gravels is a difficult one. I can only give what seems to me the most probable explanation. It appears to me probable that in the Ice Age, south of the ice sheet, the ground must have been both broken up by frosts, and also held together by being frozen hard to some depth. Then when thaws came in the short but warm summers, or when an intermission of the severe cold took place, great floods would flow down the valleys in the country south of the ice sheet, and masses of ice with frozen earth and stones would be borne along in a sort of semi-liquid flow. In this way Mr. Clement Reid explains the mass of broken-up chalk with large stones found on the heads of cliffs on the South coast, and known by the name of "combe-rock" or "head." The Ice Age was not one simple period, and it is still difficult to fit together the history we read in different places, and in particular to correlate the gravels of the south of England with the boulder clays of the glaciated area. There were certainly breaks in the period, during which the climate became much milder, or even warm; and these were long enough for southern species of animals and plants to migrate northward, and occupy the lands where an arctic climate had prevailed. There were moreover considerable variations in the relative level of land and sea. So that we have a very complex history, which is gradually coming into clearer light.