A lyrical meditation on the scientific and philosophical meaning to be found in one short stretch of Delaware coastline. This may be Ackerman's first book, but she is no novice to the art of nature writing. ``The way in to a new landscape is to pull at a single thread,'' she begins, and with quiet, acute observation and an admirable economy of style, she pulls her reader after her. The threads form a single fabric, interweaving the life of the town of Lewes with the past and future of the beaches and marshes that surround it. The impact of the man-made harbor is felt by the tiniest micro-organisms swarming in the sand. The mud flats exposed at low tide teem with life that Ackerman makes us see: razor clams and ribbon worms, mud snails and sanderlings, diatoms and rotifers. The rhythms here are ancient and mysterious, explained with reverence and some awe. The migrating red knot pauses here on its way to Arctic breeding grounds just in time to gorge on the millions of horseshoe crab eggs that have been laid under the wet sand at the spring tide. But not all of the fabric is original; this ecosystem, like most in our ever-shrinking world, has become a patchwork of native species and aggressive immigrants from the old world to the new. Nature is not the equilibrium we would like it to be--change is the only constant, and ``the wonder is that there is order or structure at all, likenesses or rules, universals on a giant scale.'' Ackerman is entranced by ``the thunder-suck of waves'' near her seaside home, and her careful, ingenuous exploration of biology and history makes the most landlocked reader appreciate it too. Poetic, precise, intelligent, thoughtful. A lovely book.