The debate was at its height when one of the most talented scientists of his generation turned his attention to it. Louis Agassiz (see the sidebar "Louis Agassiz and the Great Ice Age" on page 62) had already made a reputation based on his studies of fossil fish. In Recherches sur lespoissons fossiles (Studies of fossil fishes) he classified more than 1,700 species.
Agassiz was born in Switzerland of French parents and was very familiar with Swiss glaciers. He was also in search of attractive places to
Jean-Louis-Rodolphe Agassiz (1807-73) was born at Motier, Switzerland. He attended schools at Bienne, near Bern, and Lausanne, and he studied at the universities of Zürich, Heidelberg, Munich, and Erlangen. He specialized in the classification of fishes, and in 1831 he moved to Paris where he continued his studies, classifying fossil fishes at the Natural History Museum. He was then appointed professor of natural history at the University of Neuchätel, Switzerland.
In 1836 he turned his attention to the study of glaciers. Boulders made from rocks quite different from the underlying bedrock lay scattered on the plain of eastern France and in the Jura Mountains, on the border between France and Switzerland. Some geologists thought these boulders, called erratics, might have been pushed into their present positions by glaciers. If this idea was correct, it meant glaciers must flow like rivers and that at some time in the past they must have extended much farther than they do now. In 1836 and 1837 Agassiz and some friends observed grooves and scouring in rocks on either side of the Aar Glacier, in Switzerland, that might have been made by rocks dragged across them by movements of the glacier ice. In 1839 they found that a hut built 12
years earlier at a known position on the glacier had moved about one mile (1.6 km) and they drove a straight line of stakes into the ice across the glacier. When they returned in 1841 they found the line was U-shaped, indicating that ice at the center of the glacier had moved more than the ice at the sides.
Agassiz concluded that a great sheet of ice, similar to the Greenland ice sheet, had covered all of Switzerland and those parts of Europe where erratics were found in the geologically recent past—that is to say, within the last few million years. He published his conclusions in his book Études sur les glaciers (Studies of glaciers, 1840).
In 1846 Agassiz visited the United States to continue his studies and also to deliver a series of lectures. He remained in the United States and was appointed professor of zoology at Harvard University in 1848. He became an American citizen, and in 1915 he was elected to the Hall of Fame for Great Americans.
Agassiz found that North America had also been covered by ice. This discovery showed there had been a time when most of both Europe and North America had lain beneath vast ice sheets. He called this period the Great Ice Age.
spend his vacations, so in 1836 and 1837 he spent his summer vacations with a group of friends on the Aar Glacier, where he proved that glaciers flow.
Later he visited other parts of Europe, including Scotland, where he found further evidence of past glacial action. His observations over the next few years convinced him that glaciers had once extended over all those parts of Europe where erratics were found. He published his findings in 1840. They attracted a great deal of interest and in 1846 King Friedrich Wilhelm IV of Prussia awarded him a grant to visit the United States. There, Agassiz found similar evidence of past glaciation and concluded that a vast ice sheet had once covered a large part of North America and northern Europe. He called this time the Great Ice Age.
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