When Pre-Chellean man appeared, we shall see that the river-valleys of the Somme and Marne, in northern France, as well as of the Thames, in southeastern England, were closely similar to what they are at present in respect to their water-levels; in other words, the inland geography of Europe in the north in Chellean times and in central and southern France in the immediately succeeding Acheulean times was very much like it is at present. The superficial characters of the valleys were different; the streams in Chellean times flowed through gravels and sands, partaking of a glacial aspect; one or more of the 'river terraces' composed of sands and gravels were still sharply defined, for the soft covering of 'loam' and alluvial soil from the surrounding uplands and hills had not yet washed down to soften the outlines of the 'terraces.' Neither were the 'terraces' covered with the newer deposits of 'loess.' [Illustration: FIG. 56. Restoration of the geography of western Europe during the Third Interglacial Stage, showing the ancient land areas (dots) and the ancient river channels now submerged by the sea. Modified after Avebury's _Prehistoric Times_ by permission of Henry Holt & Co. The six white crosses (X) indicate the location of the principal Pre-Chellean stations of Piltdown on the Ouse, and Gray's Thurrock on the Thames, in England; of Abbeville, on the north bank, and St. Acheul, on the south bank of the Somme, and Chelles on the Marne, in France; and of Helin in Belgium. It will be observed that the English stations are separated from the others only by the ancient broad valley corresponding with the present English Channel.] SECULAR CHANGES OF CLIMATE IN LOWER PALÆOLITHIC TIMES We find evidences of four climatic and life phases during the long period of Lower Palæolithic evolution, as follows: 4. _Cold Moist Climate._--Advent of the fourth glaciation. Arrival of the 'full Mousterian' culture and of the Neanderthal race in Belgium and France. Repair of men to the warmer shelters, grottos, and entrances to the caverns. Final disappearance of the hardy Merck's rhinoceros and the straight-tusked elephant. Arrival of the tundra fauna, the reindeer, the woolly mammoth, and the woolly rhinoceros. Refrigeration of western Europe as far south as northern Spain and Italy. Wide distribution of cold alpine, tundra, and steppe mammals all over Germany and France, and into northern Spain. Cold tundra flora in the Thames valley, and at Hoxne, in Suffolk. Migration of the tundra mammals, the reindeer, mammoth, and rhinoceros all over southern Britain, Belgium, France, Germany, and Austria.