From the sky, the Mound of the Cross at Paquime, a 14th-century ruin in the Mexican state of Chihuahua, looks like a compass rose -- the roundish emblem indicating the cardinal directions on a map. About 30 feet in diameter and molded from compacted earth and rock taken near the banks of the Casas Grandes River, the crisscross arms point to four circular platforms. They might as well be labeled N, S, E and W...