In the Mediterranean three stages are distinguished. The Sicilian has occasional rare forms, such as Cyprina islandica and Buccinum undatum, no longer liv ing in the Mediterranean, but found in colder seas. Deposits of this age are found in the basin of Palermo, Sicily, hence the name. The Tyrrhenian has no longer any extinct species, but several living now in warmer seas. At this period the level of the Mediter ranean seems to have been about 5o to loo ft. above its present level. The third stage is that of the present-day fauna of the Mediterranean. In the Baltic sea a detailed succession has been worked out in connection with the complex history of the area— at times a fresh-water lake, at times a sea salter than at the present day. It was in the Swedish lakes left after the retreat of the ice that De Geer worked out his famous chronology, by which the duration of the stages of the Pleistocene in years can be calculated.
The Quaternary mam mals fall into four groups : (a) tundra species such as the lem ming, arctic hare, arctic fox, reindeer and musk-ox; (b) steppe species, such as jerboa, steppe marmot, horse, etc.; (c) a group of southern species—a warm fauna—including some extinct and embracing rhinoceros (several species), cave lion and cave hyena; (d) a group of extinct species including Elephas antiquus, (early Pleistocene), and Elephas primigenius (the mammoth, late Pleisto cene). It is not easy to trace the movement of Quaternary faunas, but there were living in the British Isles and Europe before the oncoming of the Ice age a number of southern and extinct species (Elephas antiquus) which appear to have retreated to the con tinent with the oncoming of the cold. In this connection it may be noted that the Strait of Dover was probably not cut through till the close of the Glacial period. Other animals, including man, retreated to caves within the British Isles (cave lion, cave bear, cave hyena). Associated with the cold conditions are the arctic animals such as the mammoth and reindeer, followed as the ice ' retreated by the gradual re-establishment of the modern fauna.
This subject is discussed elsewhere. Older Palaeolithic man (Strepian, Chellean and Acheuleen cultures) lived in the open river valleys (River Drift man) before the oncoming of the cold; newer Palaeolithic man (Mousterian, Aurignacian, Solutrian and Magdalenian culture) lived in caves. Neolithic man, with his polished stone implements, was post-Glacial and belongs to the Holocene rather than the Pleistocene.
These deposits are discussed in the article GLACIAL PERIOD. Special interest attaches
to the succession of river terraces, such as the famous series of the Thames or Somme. The First terrace of the Thames lies about 13o ft. above the present level of the river and has remains of mammoth. The Second or High (Swanscombe) terrace lies about Ioo ft. above the Thames. It has implements of Chellean and Acheuleen and possibly Mousterian types, remains of mam moth and Elephas antiquus and a number of extinct mollusca (tinio littoralis and Neritina grateloupiana). The Third or Mid dle terrace lies about 5o ft. above the Thames and has Palaeolithic "floors" with Mousterian implements. Nearly all the Mollusca are still living but mammals include the mammoth. The South or Low terrace embraces the low-lying gravels of Kew, Richmond, etc., lying 10 to 25 ft. above sea-level. The Buried Channel rep resents a period when the level of the river must have been lower than at present. The latest deposits are the extensive stretches of alluvium (Holocene).
Turning to the coastal deposits, in pre-Glacial or early Pleisto cene times the sea seems to have been higher than at present and hence there is frequently a pre-Glacial raised beach round the coasts of Britain. With the oncoming of the Glacial period the sea rose still higher and during the retreat of the glaciers the Ioo ft. raised beach, 5o ft. raised beach and 25 ft. raised beach respectively were formed, especially in Scotland. At a later date the sea sank below its present level and this is the age of the Neolithic submerged forests and buried channels. For convenience one refers to the movement of the sea relative to the land; actually the change may have been of the land in relation to the sea-level. See also GLACIAL PERIOD.
general accounts may be noted W. B. Wright, The Quaternary Ice Age (London, 1914) ; C. Deperet, "Essai de co-ordination chronologique des temps quaternaires" (C. R. Acad. Sci., Paris, March 1918—July 192o) ; K. Olbricht, "Die Eiszeit in Deutschland" (Naturwiss. Wochenschrift, Band 21, No. 27, July, 1922) ; F. Wahnschaffe and F. Schucht, Geologie and Oberflachenge staltung des Norddeutschen Hachlandes (Stuttgart, 1921) ; H. F. Osborn and Chester A. Reed, ''Old and New Standards of Pleistocene Divisions in relation to the Prehistory of Man in Europe" (Bull. Geol. Soc. America, vol. 133, 1922) ; M. Boule, Les Hommes Fossiles (Paris, 2nd ed. 1922) ; G. Dubois, "Recherches sur les terrains quater naires du Nord de la France" (Mem. Soc. geol. Nord. viii.
In these works will be found references to classical authorities. Ref erence should also be made to the writings of E. Anteos in America.
(L. D. S.)