THE PROBLEM OF ANTIQUITY OF MAN IN AUSTRALIA 13 
THE PLEISTOCENE PERIOD 
The outstanding feature of the Pleistocene or Quaternary 
Period is the series of rhythmic alternations from cold to mild 
climates which gave rise to glacial and interglacial phases. During 
the maximum glaciation, ice-caps covered most of northern 
Europe, America and Asia, and also Tasmania. Most glaciologists 
consider that glacial and interglacial phases were contempo- 
raneous in both hemispheres. In Europe four glacial phases were 
separated by mild interglacial intervals and were succeeded by 
the present post-glacial phase. Some authorities, however, hold 
that there were more than four glacial epochs in North America; 
others consider that the two first glacial phases are Pliocene, not 
Pleistocene, in age (Boule, 1923), but this is merely a question of 
nomenclature. Interglacial phases probably lasted longer than 
glacial, and the second interglacial period greatly exceeds the 
others; to this period the oldest undoubted relics of mankind 
belong. 
Several theories have been advanced to explain these climatic 
alternations, but none is generally accepted. 
Changes in relative levels of land and sea are due to one of 
two causes or to a combination of both: increase or decrease in 
the volume of the oceans (eustatic changes), and local elevations 
or depressions of the earth’s crust (tectonic movements). In 
Pleistocene times tectonic movements have been negligible in con- 
siderable areas. 
During glacial phases, withdrawal of vast quantities of water 
from the oceans to form ice-caps and glaciers lowered sea level; 
in interglacial times ice melted and sea level rose. Interglacial 
climates must have been milder than the climate of to-day since 
strandlines then formed are now raised beaches owing to eustatic 
changes in sea level. 
Daly (1934) estimated that the melting of existing Antarctic 
and Greenland ice-caps and existing glaciers would cause sea 
level to rise about 130 ft., but he pointed out that change in level 
would not be equal throughout the oceans for three reasons: 
redistribution of load on the elastic terrestrial globe causing defor- 
mation; slow transfer of plastic deep-seated matter consequent on 
that deformation; and cessation of gravitational pull on adjacent 
ocean waters by ice-caps. For the same reasons, the estimated 
quantity of water withdrawn or set free during glacial and inter- 
glacial phases can give only a rough indication of corresponding 
changes of sea level in any particular locality. 
During glacial phases boulder-clay (tillite) accumulated beneath 
ice-caps, terminal moraines were formed at the margins of ice- 
