Philip Kopper is an ex-Washington Post reporter with a penchant for beaches and the knack of sounding like John Leonard cross-examining himself or Loren Eiseley cross-examining the Universe. But he isn't peddling thoughts; he's produced an introduction to the commonplaces of Atlantic beaches from Maine to the Outer Banks. With due attention to Linnaeus and the intricacies of taxonomy (""Think of it as an unspeakably big family tree""), he takes up in turn the crabs, the mollusks, the fishes, the birds, the incidental reptiles and mammals. Scallops, he observes, ""bounce about in the water like silent castanets clapping their valves."" Bird-brained or not, ""each bird is a virtuoso of instant reaction to every kind of natural physical circumstance."" And, in the did-you-know category, fish scales ""become marked with rings which, like a tree's, can be read to interpret age."" Still less conventional is Kopper's attention to the physical beach. A chapter explains how the shore persists despite constant buffeting. Another considers the bizarre ""mâ‰¤nage â€¦ trois"" of fertile ocean shallows, sterile beachsand, and fertile salt marsh. Later, with beach-going in mind, Kopper points out the hazards, beginning with the surf--here, his advisor is the chief lifeguard at Assateague. Interspersed among the casual, systematic examinations of one or another topic are ""Driftwords""--brief, elegant reflections on anything from the Big Bang to nude bathing. With meticulous drawings by Anne E. Lacy, a truly personal reference that's informative and seductive in equal parts.