Dr. Halliday's liberally bubbling fascination with caves is heady enough to get casual readers out exploring, for there are caves everywhere in the States within weekend driving distance. There are commercial caves, and then there are caves. These are of the hair-raising variety, both in beauty and black abysses of danger. Halliday covers all the major cave systems in the country. The most difficult cave to negotiate is Virginia's Schoolhouse Cave, whose 200-foot drop-offs demand mountain-climbing equipment and whose hellish elaboration into the bowels of the earth takes up to 20 hours to penetrate. Cave exploration has only recently come into its own, as well as cave discovery. Many are found by sheer accident. The story of Mammoth Cave, of Carlsbad Cavern, of crystal caves, sandstone caves, windy and breathing caves, and of as yet unplumbed monsters, justifies Halliday's sometimes hyperbolic style. There is also an excellent chapter for gentle beginners which will help them wind up in the right direction; i.e. back out again. Most of the books about caves have been at the juvenile level, with the exception of Roy Pinney's worldwide Complete Book of Cave Exploration (Coward-McCann-1962). Mr. Pinney was more authoritative. Halliday is more dramatic.