over, salt deposits in the Arctic regions indicate an ancient desert climate.
Either the climate in the past altered dramatically or the continents shifted
positions with respect to the equator.
During the early part of the glacial epoch, the maximum glacial effects
were in South America and South Africa. Later, as the continent drifted
southward, the chief glacial centers moved to Australia and Antarctica,
clearly showing that the southern continents that comprised Gondwana
hovered over the South Pole. Continents residing near the poles is often the
cause of extended periods of glaciation. This is because land at higher lati-
tudes has a high albedo (reflective quality) and a low heat capacity, encour-
aging the accumulation of ice.
Ice sheets covered large portions of east-central South America, South
Africa, India, Australia, and Antarctica. In Australia, marine sediments were
interbedded with glacial deposits. Tillites were separated by seams of coal.
These indicate that periods of glaciation were interspersed with warm inter-
glacial spells, when extensive forests grew. In South Africa, the Karroo Series,Figure 113Ice shelves of
Daniell Peninsula,
Victoria Land, Antarctica.
(Photo by W. B. Hamilton,
courtesy USGS)
Historical Geology