Gr 6-9-- Two titles that will attract readers' interest. Both assemble, organize, and simplify material from a wide range of sources, but their in-text references to names and events are chiefly signposts to novices for further searching. Arvey's book examines real and imagined threats to continued life on Earth or to the planet itself. Brief chapters survey prophecies and predictions; comets, earthquakes, and glaciers; pollution; and nuclear winter. Cohen's Prophets of Doom (Millbrook, 1992) adds plagues, emphasizes prophecies, and has more information on the Millerites, Nostradamus, etc. (The Swift-Tuttle comet is too recently in the news for inclusion in either.) O'Neal offers one chapter on the possible reality of Arthur's existence, but considers other facets of the legend, with good sections on the Round Table and the Holy Grail that supplement Andronik's Quest for a King (Atheneum, 1989).) Inviting in format and appealing for browsers, these books provide a jumping-off place for report writers and debaters. --Ruth M. McConnell, San Antonio Pub . Lib .