That the pre-Columbian peoples of Mesoamerica were familiar with the property of magnetism has been suggested by several researchers, among them the geographer Robert Fuson and the anthropologist Michael Coe. Indeed, a flattened oblong piece of hematite discovered during Coe’s excavation of the Olmec site of San Lorenzo in southern Veracruz state in 1966 has been thoroughly examined by John Carlson, who suggests that it probably was fashioned for use as a compass. (In tests, however, it never aligned more closely than about 35° with the Earth’s magnetic field.) In 1975, a basaltic sculpture at the site of Izapa, on the Pacific coastal plain of Mexico near the Guatemalan border, was found to possess a strong magnetic field. Variously described as being the representation of either a frog (Norman, 1976) or a turtle’s head (Malmström, 1976), it has a north-seeking pole in its snout and a south-seeking pole at the back of its head. The discovery led the latter researcher to speculate that...