SIDEWALK FOSSILS

If there's a case for studying the leaf, shoe and paw prints, the sketches, street names and graffiti to be found embedded in sidewalks, Sommer doesn't make it. Nor will urban naturalists be enlightened to learn that ""different sneakers have different patterns on their soles."" Instead of peering down to determine whether a pointed toe and small heel indicates a woman's shoe, we'd just as soon play hopscotch.