To transform themselves into a globe or ball of fire was, as we have seen (antè, p. 21), a power claimed by expert nagualists, and to handle it with impunity, or to blow it from the mouth, was one of their commonest exhibitions. Nothing so much proved their superiority as thus to master this potent element. =30.= The same name above referred to, “the Heart of the Town,” or “of the Hills,” was that which at a comparatively late date was applied to an idol of green stone preserved with religious care in a cavern in the Cerro de Monopostiac, not far from San Francisco del Mar. The spot is still believed by the natives to be enchanted ground and protected by superhuman powers.[46-§] These green stones, called _chalchiuitl_, of jadeite, nephrite, green quartz, or the like, were accounted of peculiar religious significance throughout southern Mexico, and probably to this day many are preserved among the indigenous population as amulets and charms. They were often carved into images, either in human form or representing a frog, the latter apparently the symbol of the waters and of fertility. Bartholomè de Alva refers to them in a passage of his Confessionary. The priest asks the penitent: “Dost thou possess at this very time little idols of green stone, or frogs made of it (_in chalchiuh coconeme, chalchiuh tamazoltin_)? “Dost thou put them out in the sun to be warmed? Dost thou keep them wrapped in cotton coverings, with great respect and veneration? “Dost thou believe, and hold for very truth, that these green stones give thee food and drink, even as thy ancestors believed, who died in their idolatry? Dost thou believe that they give thee success and prosperity and good things, and all that them hast or wishest? Because we know very well that many of you so believe at this very time.”[47-*] Down to quite a recent date, and perhaps still, these green stones are employed in certain ceremonies in vogue among the Indians of Oaxaca in order to ensure a plenteous maize harvest. The largest ear of corn in the field is selected and wrapped up in a cloth with some of these chalchiuite. At the next corn-planting it is taken to the field and buried in the soil. This is believed to be a relic of the worship of the ancient Zapotec divinity, Quiegolani, who presided over cultivated fields.[47-†] They are still in use among the natives as lucky stones or amulets. In the Zotzil insurrection of 1869, already referred to, one was found suspended to the neck of one of the slain Indians. It came into the possession of M. Maler, who has described and figured it.[47-‡] It represents a human head with a curious expression and a singular headdress.