But if the Mediterranean area has been depressed to an amount of from 2,000 to 3,000 feet since the pleistocene age, we have proof that the region to the south has been elevated to that extent in comparatively modern times. Mr. Maw,[258] in his journey in 1873 to the Northern Sahara, observed raised beaches at a height of 2,000 feet, and loam and shingle-beds as high as 2,700 feet. He therefore concludes that the part of the Sahara which he explored had been raised at least 3,000 feet above the sea. These changes of level, the same in amount, but in opposite directions, were probably compensatory and simultaneous. Northern Africa may have been cut off from the central and southern portions of the continent by the sea extending over the Sahara, during the time that the Mediterranean was represented by the two inland salt lakes figured in the accompanying map (Fig. 129). And while the region of the Sahara was being elevated, that of the Mediterranean was probably being depressed. These changes in the relation of sea to land, and the greater elevation of the mountains in the neighbouring countries, must have affected not merely the climate of southern, but also of north-western Europe, and ought not to be left out of account in any theory relating to pleistocene climate. CHAPTER XI. THE EUROPEAN CLIMATE IN THE PLEISTOCENE AGE. The evidence of the Mammalia as to Climate.--The Southern Group.-- The Northern Group.--Probable cause of Association of Northern and Southern Groups.--The Temperate Group.--Species common to Cold and Tropical Climates.--Extinct Species.--Two Periods of Glaciation in Britain.--Three Climatal Changes represented on the Continent.--Europe invaded by Pleistocene Mammals before the Glacial Period.--Mammals lived in Britain during the Second Ice or Glacial Stage.--The Glacial Period does not separate one Life-era from another.--Relation of Palæolithic Man to Glacial Period.--Age of Contents of Caves in Glaciated Districts. _The Evidence of the Mammalia as to Climate._ In the last three chapters we have seen that the cave-mammalia throw great light on the pleistocene geography of Europe, and that there is reason for the belief that the land surface then extended northwards and westwards, so as to include Ireland; and southwards to join Africa, in the direction of Sicily, Malta, and Gibraltar. We must now pass on to the consideration of the climate on this great continental area, which would allow of so large and varied a fauna existing in our quarter of the world. _The Southern Group of Animals._ The pleistocene fauna is remarkable for the mixture of species. It consists of forms now banished to South Africa, Northern Asia, and America, or to the severe climate of high mountains, mingled with those which lived in Europe in the historic age, and those which have wholly disappeared from the face of the earth. We will take the living species first.