SONGS OF THE NORTH by Sigurd Olson, edited by Howard Frank Mosher (Penguin: $11.95, 267 pp., illustrated). Naturalist Olson celebrates the beauty of the Quetico-Superior region in a well-chosen collection of essays drawn from six of his books. Evoking the memory of the voyageurs, the bold woodsmen who crisscrossed North America in the heyday of the fur trade, he describes the woods, streams, lakes and animals of northern Minnesota. Reveling in the silence of the remote forests, Olson savors "the feeling of a great waterway and the men who traversed it long before our time. Theirs was a slow pace with time to absorb the terrain itself, its smells and sights and sounds, the intangible impressions that come only when a man moves slowly under his own power across the face of the Earth."