Another souvenir of he Ice Age, though of quite a different sort, is preserved at Sleeping Bear Dunes National Lakeshore. There, on the eastern coast of the Lake Michigan, winds have piled up enormous dunes of glacier - made sand. Some of the dunes tower more than 450 feet above the lake and command majestic views of the twin Manitou Islands far offshore. According to Indian legend, the area took shape when a mother bear and two cubs tried to flee a forest fire by swimming across Lake Michigan. The mother, it is said, made it to shore, where, transformed into a gigantic dune, she still awaits her offspring. But the hapless cubs drowned before reaching land, and can seen today as the two islands.

AN ECOLOGICAL BALANCING ACT.

Isle Royale, the largest island in Lake Superior, is more than a scenic national park. It is also a unique natural laboratory where animals, cut off from the mainland, play out the drama between predator and prey and, in the process, enable scientists to observe nature's ecological balancing act.

As late as the 1940's, foraging herds of moose on the island had no natural enemies. As a result, they multiplied so rapidly that they almost wiped out the stands of yew and the balsam that provided their food.

When the animals' very existence seemed threatened, salvation came along in an unexpected form: a pack of predatory wolves that crossed the frozen lake to the island around 1949. Since then, wolves have consistently thinned the moose population, usually attacking those weakened by age or disease. At the same time, healthy moose have kept the wolves in check with they lethal hooves. The result: naturally controlled populations of moose and wolves, with survival assured for both.