the world we take for granted was, until very recently, frozen solid. As I write this in Massachusetts, the evidence surrounds me, plain to see. Massive boulders unceremoniously dropped by the glaciers dot the deep woods, town centers, and beaches throughout New England. Kettle ponds mark the spots where large solitary hunks of ice, orphaned by the great ice sheets, were left behind to melt in their tracks. The winter world is evident in the grooved lines, called striations, etched in the bedrock of the mountains of New Hampshire, where mile-thick grindstones of ice advanced and retreated,
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