With the exception of the Hiroshima bomb and Darwin's voyage on the Beagle, few developments of science have had as great an impact upon the human imagination as Agassiz's announcement in 1837 that currently habitable portions of the earth had been covered in geologically recent times by ice sheets thousands of feet in thickness and covering millions of square miles. At first hotly contested, the postulate finally gained universal acceptance because of such indisputable evidence as typically glacial till, drift, and boulders transported hundreds of miles from their bed‐rock origins; deep abrasion markings on the surface of bed‐rock recording the grinding flow; moraines and hills of glacial deposits along with typical lakes, rivers, and so forth.

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