Eleven thousand years ago, a glacier rolled over what is now the Canadian border, strewing great granite boulders over the landscape carving a thousand crystal lakes in the wilderness. Later, the Chippewa Indians came and went, leaving red pictographs on the rock ledges French voyageurs, their canoes laden with furs from the Northwest, glided through on their way to Montreal.

Today, it is still possible to slip into northern Minnesota's Boundary Waters Canoe Area for 24 hours, turning back the clock to primeval America.

At first, city eyes, accustomed to the glare of pavement and the fine print of documents, see only a mass of green and a mass of blue. Slowly, within the green, dense forests spread out from open bogs. Within the forest, the narrow silver trunks of aspen and birch shine through the pine trees.

There are differences, it soon becomes apparent, between spruces and balsams, between red pines and white pines and jack pines. The needlesare long or short, light or dark, feathery or spindly. Each cone, bark, root is distinct. Some trees are dead from last year's drought.

The lake that glides under the canoe isn't really blue, except under the midday sun. In the morning it mirrors the white mist. It shines copper under the sunset. When the shadows fall a polished obsidian comes to mind.

City ears, dulled by the rush-hour din, hear nothing at first. There are no voices, no clacking typewriters, no honking horns, so it must be quiet. It takes a while, but soon the silence isn't silent at all. Water splashes against the rocks, mosquitoes whine, trees rustle. And, from every direction, an incomprehensible polpphony of birdsongs.

More than 100 species fly here from the tropics, covering 300 miles a day in their rush toward summer nesting grounds. People who care about such things have counted 22 species of warbler in the Boundary Waters, each one a freak of evolution. They can be told apart, not only by the different colors that camouflafe them from predators and the various sounds they make but by the fact that one feeds only in the top third of a certain tree, another, only in the bottom third for reasons man has yet to discover.

The wilderness seems immobile at first. It is, on a grand scale. But movements is everywhere if one looks for it. On the smooth surface of the lake, a centimeter-long whirlygig beetle waltzes from side to side, leaving a swooping pattern in his wake. Sunlight glimmers silver-green in the grooves of the ripples. A black spider crawls up the side of a pink granite boulder.

Except for a great blue heron feeding by the shore, and a turkey buzzard circling overhead, the animals and birds are in hiding. "Quick 0 three beers," as Minnesotans have labled the song of the olive0sided fly0catcher, peals out of the trees, but the bird is nowhere in ishgt. The wolves and bears don't come out until night-fall and the moose are shy of hunters. Even the beaver huts, carefully assmbled with twigs and mud, show no sign of life.

After a mile-long portage, the back is bruised from a heavy load. A swim at dusk is in order before setting up camp. A quarter mile out, the water is cool enough to absorb the stress of the day. A hundred feet away, a striped loon looks up and glides over with obvious curiosity. As we swim closer, curious, too, the bird shrieks with giddy laughter, a cry that has haunted many a camper in the wilderness. Bottom up; it pops quickly beneath the water and disappears.