Two dozen mountains drape themselves diagonally across the middle of Acadia National Park on Mount Desert Island in Maine. The peaks start near Bar Harbor in the northeast, tumble down across Jordan Pond, Somes Sound, and Echo Lake, and end with Mansell and Bernard Mountains in the southwest. Every one of these mountains, like the state of Maine, all of New England, and much of the continent of North America, has been scoured by glaciers during multiple ice ages of the past. The most recent glacier began its retreat about 17,000 years ago.
In the mid-19th century, the Swiss-born geologist Louis Agassiz visited Maine on a vacation from Harvard University. The glacier-scoured bedrock formations on Mount Desert Island gave him plenty of evidence to support his theory of the Ice Age: that enormous glaciers, rather than a flood, had once covered much of Europe and North America. A few years after his visit, in 1867, Agassiz published two essays on “Glacial Phenomena in Maine” in The Atlantic (part I, part II). He used a French term to name what he saw, calling the glacially shaped formations roches moutonnées. The meaning of this term has caused confusion in geology ever since.
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To this day, many geologists follow Agassiz in considering all the rounded peaks and outcrops on Mount Desert Island to be roches moutonnées. Other geologists, including Duane and Ruth Braun, the co-authors of Guide to the Geology of Mount Desert Island and Acadia National Park, reserve this curious French term for the most distinctly asymmetrical of the mountains, ones with a long gradual slope along the northern “up-ice” side (the direction from which the glacier advanced) and cliffs on the lee or “down-ice” side. A mountain known as the Beehive, whose steep, plucked, south-facing cliffs terrify hikers with vertigo, illustrates the accepted American definition of roche moutonnée.