A leisurely tour of the coral reefs of Grand Turk Island, where novelist Harrigan (Jacob's Well, 1984) learns about nature and himself. Diving has always meant a great deal to Harrigan, but now, living far from the sea and worried that the activity is becoming nothing more than a hobby, he decides to spend an extensive period diving in the Caribbean. There, he will ``study the natural history of the coral reef, but the motivation was not as clear or, perhaps, as worthy. I wanted to be, at least for a time, my underwater self.'' He checks into a local motel on the island--a desolate and relatively unspoiled place where salt was once collected from inland pans--and begins his diving explorations. As he explores the reefs, dives down part of the great wall that edges the nearby 7,000-foot-deep channel, and chats to locals, Harrigan relates old diving adventures as far apart as Australia and Mexico. He observes the variety of fish and plant life, explains that coral is actually an animal, not a plant, and includes such diving lore as the story of the development of the aqualung--an invention that, as Jacques Cousteau wrote, meant that ``From this day forward we would swim across miles of country no man had known.'' Catching conches for his dinner, Harrigan laments the decline of the sea-turtle, ``a great being, venerable, unknowable,'' and admits to being angry with dolphins because he fails to interest them. Hoping to be transformed by the reef, his underwater destiny acknowledged, he ruefully realizes how indifferent the teeming underwater world is to his presence. He is ready to go home. A graceful and low-keyed celebration of diving and the dazzling underwater world it reveals, as much for the underwater enthusiast as for the armchair traveler.