PLEISTOCENE , ingeology, the epoch which succeeded the Pliocene; it is the last of the
See also:Tertiary periods, and hence the
See also:lower subdivision of the
See also:quaternary or
See also:modern era . The name was introduced by
See also:Sir C .
See also:Lyell in 1839 (from Gr . 7r)^Ei(TTov, most, and uatvbs,
See also:recent), the rocks of this
See also:period containing a higher percentage of living forms than the youngest of the Tertiary formations . By many writers " Pleistocene " has been regarded as synonymous with " Glacial Period " or the " Diluvium " of some geologists . In the
See also:northern hemisphere the protracted period of glaciation, with its predominating influence upon modern topography and faunal distribution, was undoubtedly the outstanding feature of the
See also:time . The phenomena of the Glacial period (q.v.), which was by no means strictly limited to the northern latitudes, are dealt with under that
See also:head, but there are certain other characteristics of the Pleistocene period which bear no
See also:direct relationship to glaciation, and these will be dealt with here . The gradual inception of colder conditions in the northern hemisphere which lead up to the more extreme conditions of glaciation clearly began in the latter
See also:part of the Pliocene period, and the effects of this cooling are seen not only in northern
See also:Europe and
See also:America but as far south as the Mediterranean . The result of this is that there is a certain indefiniteness as to the exact
See also:line to be adopted for the Pleistocene formations; thus the
See also:Bed of Cromer and certain beds in
See also:Sicily and Italy are by some authors placed in this period and by others in the Pliocene (q.v.) . Again it is clear that in parts of northern Europe,
See also:Siberia and
See also:North America, the conditions characteristic of a glacial period are still existent; even in Scotland and Norway the last traces of glacial
See also:action are remarkably fresh, and the last remnants of
See also:great glacial centres still linger in the
See also:Alps and other lofty
See also:southern mountains . Many of the formations of this period can be shown by their fossil contents to belong to early quaternary time, but since so many of these deposits are strictly
See also:local in character, and since the
See also:fauna and
See also:present in any one spot have been determined by local
See also:geographical conditions which have assisted or retarded the
See also:migration of certain forms, it is a
See also:matter of extreme difficulty—one may say impossibility—to reduce the Pleistocene formations to any generally applicable
See also:order . For similar reasons it is impossible to define strictly the upper limit of the formations of this period, and to say where the Pleistocene ends and where the Recent or Holocene period begins .
Thecomposition and distribution of the Pleistocene fauna and flora present many points of extreme
See also:interest . The feature of greatest importance is that man existed somewhere and in some
See also:condition before and in this period; but no really satisfactory
See also:proof has so far been forthcoming which will set back his first appearance before the beginning of the glacial peripd (Pithecanthropus erectus found by E .
See also:Dubois in
See also:Java is regarded as of Pliocene age) . The presence of the remains o man or of his
See also:works might reason-ably be taken as a criterion of the Pleistocene age of a deposit—if we omit the remains of
See also:historical time . But here again it has to be
See also:borne in mind that historical time is continually being set back by archaeological
See also:research, and further, the difficulty of employing artefacs of
See also:stone as chronological indicators is shown by the fact that even at the present
See also:day implements of stone are still in use, and that different local races of early men must have been in diverse stages of development in Pleistocene as in later ages . It is, therefore, only with the utmost caution that chronological subdivisions of the period, such as those mentioned below, based' upon the
See also:form and degree of finish of stone implements, can be used in anything but local correlations unless the evidence is supported by satisfactory fossils . Next to the appearance of man the most striking characteristic of the
See also:land fauna was the existence of numerous large-bodied mammals; Elephas antiquus, for instance, attained a more excessive bulk than any other proboscidean either before or since, the woolly
See also:rhinoceros, the great hippopotamus, the cave bear, cave lion and
See also:deer were all larger than their living representatives . No less striking is the disappearance of these large forms together with highly specialized creatures such as
See also:Machaerodus within the same period, through the action of the same causes which had re-moved the bulky and specialized
See also:reptiles of an earlier
See also:geological period . The Pleistocene mammalia of Europe include Elephas antiquus, E. primogenius (
See also:mammoth), R. antiquitatis (tichorhinus) (the woolly rhinoceros), R. mercki (especially in
See also:Silesia), R. leptorhinus (south-east Europe), Elasmotherium (Silesia and south Russia), Hippopotamus major,
See also:Bos primigenius (aurochs,
See also:extinct in historical time), Bison
See also:priscus, Bison europaeus (still living in the
See also:Caucasus and Lithuania), Bos (Bubalus) pallasi (north Europe), camels in south Russia and Rumania, Equus fossilis and varieties, Cervus (Megaceros) giganteus (= hibernicus) (the great Irish "
See also:elk " and its varieties) ; Cervus elaphus, C. aleus, Rangifer tarandus and R. groenlandicus (
See also:reindeer), Capreolus caprea, Capra
See also:Saiga tatarica, Ovibos moschatus, Felis spelaeus, Hyaena spelaea, Ur-
See also:sus spelaeus,
See also:glutton, hare,
See also:lemming (Myodes torquatus and M. lemmus), Spermophilus, Alactaga, Arctomys,
See also:Castor fiber, Lagomys, Trogontherium . In North America there were numerous mammals
See also:common to Europe and North
See also:Asia, including the
See also:musk-ox, mammoth and
See also:horse ; the mastodon held on into this period in America but not in Europe; there were also lamas, tapirs, camels (Camelus auchenia), Machaerodus, Mylodon, Procyon, Alces . In South America there was at first a very characteristic endemic fauna including Megatherium, Mylodon, Grypotherium, Lestodon, Toxodon, Typotherium, Glyptodon,
See also:Rhea, to which were added later, Mastodon, Machaerodus, Lama and other North
See also:American forms . In
See also:Australia a very distinct assemblage of large marsupials and monotremes lived in the Pleistocene period; including Phascolus, Diprotodon, Thylacoleo, Nototherium and a large extinct
See also:Echidna; placental mammals were not then known in this region .
See also:Madagascar the Aepiornis, Megaladapis, and certain extinct lemuroid creatures have
See also:left their remains . The advance and retreat of glacial conditions in northern latitudes had a marked influence upon animal and plant
See also:life, and was the means of determining the present distribution of many of the living mammalia and
See also:plants; some were driven permanently southward, some northern forms still live isolated on the higher
See also:mountain regions, others like the reindeer and musk-ox returned northward as soon as the conditions permitted . The apparently curious admixture of what are now often regarded as tropical or sub-tropicalforms (lion,
See also:hyena, rhinoceros and elephants) with
See also:cold-temperate or arctic genera, presents no real difficulty, since their distribution was doubtless merely a matter of
See also:food supply; and some of these, like the woolly rhinoceros and mammcth, were provided with a thick hairy pelt . Although in the
See also:main the arrangement of land and
See also:sea was little different from that which obtains at the present time, one or two features existed in the Pleistocene period which had a considerable influence on faunal migration . For instance, the
See also:absence of the
See also:Bering Straits permitted
See also:free communication between Europe and North America, and the absence of the Straits of
See also:Dover allowed a similar interchange between Great Britain and France; while an extension of the sea in the
See also:Caspian region and of the Arctic Sea in northern Russia acted as a
See also:bar to free passage between Europe and Asia in those regions . The formations of Pleistocene age, other than those of direct glacial origin, include deposits on the floors of caves in
See also:limestone and dolomitic rocks, calcareous
See also:sinter (travertine or tufa) formed by springs,
See also:river and lake alluvial and lacustrine terraces, elevated marine beaches, submerged forests, ancient lake deposits and
See also:peat beds,
See also:loess and sand
See also:dunes . Some of the prevalent styles of classifying the deposits of the glacial formations of this period are mentioned in the article GLACIAL PERIOD . The following subdivisions are often employed by
See also:European geologists: a younger division, Reindeer time =Magdal6nieni stage; a
See also:middle division, Mammoth time=Salutreen2 stage; and an older division, Elephas antiquus time=Chell6en3 stage . While some authors include all the above in the " glacial period," others would place the Magdalenien in a
See also:post-glacial division . The. terms Magdal6nien, &c., are really archaeological, based upon the characters of the implements found in the deposits, and like the similar terms " eolithic " and " palaeolithic "they are of little value in geological chronology unless they are supported by palaeontological evidence . See E .
See also:Geinitz, Das Quartar von
See also:Europa (
See also:Stuttgart, 1904), with very full references; T .
C . Chamberlin and R . D .
See also:Salisbury, Geology, vol. iii . (New
See also:York, 1906), for references to American authorities . U . A .
PLEONASM (Gr. srAeovaoµbs, from 1rXeova?'ecv, to a...
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