Cape Cod's vast outer coast, named The Great Beach by Henry David Thoreau, is little changed since the Pilgrim's first landfall almost 350 years ago. Today a plane can skim its fifty miles in a matter of seconds, and in the summer bathing areas are so crowded with cars and people they take on a continental flavor. But the long, desolate, windswept stretches can still be found, and the National Park Service has been taking steps to preserve the original character of the beach and its rolling dunes back from the water, designating it a National Seashore.