How the Scientist Thinks

Darwin and a fellow scientist were searching for fossils in the north of England. They were not aware of the glacial theory at the time. Years later Darwin revisited the area, and he was now astonished to discover how clearly marked were the glacial ridges on the rocks. He had not noticed them on his earlier visit because he was not looking for them.... Darwin was able to appreciate the glacial markings only after he became aware of the glacial theory.

Lionel Ruby, "How the Scientist Thinks." In From Paragraph to Essay. Ed. Woodrow Ohlsen and Frank L. Hammond. New York: Charles Scribner's Sons, 1966.

• Glacial Theory
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