'Ancient glaciers did not travel alone. They carried within them pebbles, rocks, even boulders, sometimes for hundreds of miles. These migrating stones, once deposited, are called “erratics” — they stick out among their new surroundings. When the Cordilleran ice sheet worked its way down the mountains of Alaska and across western Canada, it melted to reveal a trail of angular stones now known as the Foothills Erratics Train.' (Introduction)