Unlike the scientists who at that time conducted the Geological Survey of California and who believed that cataclysmic eruptions had given birth to the valley, Muir was the first to realize that glaciers – slowly moving giants of ice – had carved it out over thousands of years. Muir began to read the glacial footprints and scars on the rocks. When he found a living glacier, he proved his theory of glacial motion in Yosemite Valley by placing stakes into the ice which moved several inches over a period of forty-six days.
