14 THE PROBLEM OF ANTIQUITY OF MAN IN AUSTRALIA 
sheets and glaciers, and fluvio-glacial sands and gravels (outwash- 
aprons) spread beyond the moraines. Lowering of sea level 
changed parts of the continental shelves into dry land and exposed 
large areas of sand which was then blown by the wind and gave 
rise to dunes. In cold dry areas thick beds of dust (loess) accumu- 
lated, as they are doing to-day on the steppes of Southern Russia 
and Siberia; other regions, now arid, had abundant rainfall. River 
erosion became active and river valleys were deepened in response 
to low sea level. 
During interglacial phases sea level rose, low-lying country was 
submerged, and new coast lines were established at higher levels. 
The flow of rivers was checked and alluvium was deposited in 
their valleys. 
In response to these climatic and geographic changes, plants 
and animals, including mankind, migrated to and fro. Some 
species died out; of the genus Homo only H. sapiens survived. 
Daly (1925) considered that in post-glacial times a world-wide 
strandline at about 10-20 ft. above present sea level was formed 
during a slight general fall in temperature about 4,000 years ago 
when water was abstracted from the oceans to thicken existing 
ice-caps; Milankovitch’s radiation curve indicates about 10,000 
years. Wright (1937), however, has brought forward evidence to 
show that the 15-foot raised shoreline of Western Europe is pre- 
glacial, not post-glacial nor interglacial. 
In many regions evidence of the early glacial and interglacial 
phases has been obliterated wholly or in part by erosion during 
succeeding phases, and correlation of raised beaches with river 
terraces, and of drowned valleys with glacial phases consequently 
presents many problems. The highest raised beaches due to eustatie 
changes are not necessarily the oldest, but they must rather be 
correlated with the mildest interglacial phase.® 
If climate is governed by periodic changes in the orbit of 
the earth, there are astronomic data for estimating Pleistocene 
chronology in years (Zeuner, 1935); the method is based on 
detailed stratigraphical investigations of glacial deposits, river 
terraces and loess in Central Europe, and on Milankovitch’s 
(1930) solar radiation curve (Fig. 1). This curve (Fig. 1) is the 
mathematical solution of a problem in astronomy concerning 
periodic changes in some elements of the earth’s orbit that cause 
corresponding fluctuations in the total radiation received by the 
earth from the sun. The period covered is the past 600,000 years. 
Changes in Pleistocene climates indicated by the full geological 
5. For general accounts of the Pleistocene, see Boule (1923), Soll 92 
and Wright (1937). ee er a ee) 
