Reaching and exploring these depths may well take longer than reaching and exploring the moon,"" says Mr. Weiss in reference to the undersea mountain ridges called continental shelves. This remark is the only departure from currency in a fine small book that eclipses other juvenile oceanographies in its directness, immediacy, and accessibility to quite young readers. Including even the summer-1969 voyage of silent-sub Ben Franklin in its tale of Sealabs I, II, and III, the study proffers scientific data without calling attention to it: pressure-control developments, the ocean's food-chain and its natural resources, the Piccards' ""underwater balloon"" invention known as a bathyscape, background on the International Conference on the Law of the Seas. Diverting stories--Scott Carpenter's transformation from astronaut to aquanaut; Tuffy the messenger-dolphin--and visual aids (photos, maps, diagrams, drawings) are combined in this responsible approach from a man with a good sense of humor and a nice way with descriptions. All addressed to the child who'd drown in less well-charted waters.