We may sooner know the secrets of the moon than of Stonehenge…. Setting up ["The Mystery of Stonehenge"] as an informal inquiry, Franklyn Branley carefully sifts through archeological findings, scientific data and informed speculations, picking out the clues that shed a little light on Stonehenge's shadowed past. How did Stone Age men haul granite slabs, weighing 40 tons, without the wheel? And without metal tools, how did they cut and carve and then erect them vertically and horizontally? Was the site an ancient sun temple, or a sepulchral ground, or an astrological observatory? Mr. Branley doesn't come up with final answers to these centuries-old questions nor does he take a stand on present-day controversy. Still he has ably described the way primitive people may have achieved an engineering feat that in its time rivals today's space program.