Some of the most enigmatic human-made objects from Europe's late Stone Age — intricately carved balls of stone, each about the size of a baseball — continue to baffle archaeologists more than 200 years after they were first discovered. More than 500 of the enigmatic objects have now been found, most of them in northeast Scotland, but also in the Orkney Islands, England, Ireland and one in Norway. Archaeologists still don't know the original purpose or meaning of the Neolithic stone balls, which are recognized as some of the finest examples of Neolithic art found anywhere in the world. But...