129
Agassiz was the first to suggest
that large erratics, such as these in the
Caher Valley of Ireland, were deposited
by ancient glaciers.See also: WIlliam Smith 115 ■ Alfred Wegener 222–23
A CENTURY OF PROGRESS
could not explain was why such
features were found in areas on
Earth that had no glaciers. One
theory argued that rocks were
moved by repeated flooding. Floods
could explain the “boulder drift”
(the sands, clays, and gravels that
included erratic boulders) that
overlay much of the bedrock of
Europe. The material might have
been deposited when the last flood
retreated. The largest erratics could
have been caught up in icebergs,
which deposited the rocks when
they melted. But the theory could
not explain all of the features.
The ice age revealed
During the 1830s, Swiss geologist
Louis Agassiz spent several
vacations in the European Alps
studying glaciers and their valleys.
He realized that glacial features
everywhere, not just in the Alps,
could be explained if Earth had
once been covered in far more
ice than at present. The glaciers
of today must be the remnants of
ice sheets that had at one time
covered most of the globe. But
before he published his theory
Agassiz wanted to convince others.
He had met William Buckland, a
prominent English geologist, while
excavating fossil fishes in the Old
Red Sandstone rocks in the Alps.
When Agassiz showed him the
evidence for his theory of an ice
age, Buckland was convinced,
and in 1840 the two men toured
Scotland to look for evidence of
glaciation there. After the tour,
Agassiz presented his ideas to
the Geological Society of London.
Although he had convinced
Buckland and Charles Lyell—two
of the leading geologists of the
day—the other members of the
society were unimpressed. A nearly
global glaciation seemed no more
probable than a global flood.
However, the idea of ice ages
gradually gained acceptance, and
today there is evidence from many
different fields of geology that ice
has covered much of Earth’s
surface many times in the past. ■Louis Agassiz
Born in a small Swiss village
in 1807, Louis Agassiz studied
to be a physician, but became
a professor of natural history
at the University of Neuchâtel.
His first scientific work, under
the French naturalist Georges
Cuvier, involved classifying
freshwater fish from Brazil,
and Agassiz went on to
undertake extensive work
on fossilized fish. In the late
1830s, his interests spread
to glaciers and zoological
classification. In 1847, he took
a post at Harvard University
in the US.
Agassiz never accepted
Darwin’s theory of evolution,
believing that species were
“ideas in the mind of God”
and that all species had been
created for the regions they
inhabited. He advocated
“polygenism,” a belief that
different human races did not
share a common ancestor, but
were created separately by
God. In recent years, his
reputation has been tarnished
by his apparent advocacy of
racist ideas.Key works1840 Study on Glaciers
1842–46 Nomenclator
Zoologicus