In the collections of the Museum of the American Indian, Heye Foundation, are three mirrors faced with highly-polished marcasite on their original matrices, apparently slate--the only specimens of this character that we have seen. Two of these mirrors, which were collected by William Niven from ancient graves near Iguala, Guerrero, are perforated for suspension, and all three average five inches in diameter and a quarter of an inch in thickness. With these mirrors were found numerous little unpolished cubes of iron pyrites, which may have been intended for use in mosaic-work. There are, however, a number of rather thin, flat, irregularly shaped pieces, with very thin matrix of stone, and with beveled edges, which unquestionably have been parts of mirrors made in mosaic fashion similar to those found in the Cuilapa grave, the only difference being that the inlays from Iguala are larger and thicker than those on the Cuilapa specimens, which are simply thin sheets of hematite. The region where the Iguala specimens were discovered was probably the seat of a people of Nahuan culture. [Illustration: PL. XVIII MASK OF HUMAN SKULL WITH MOSAIC DECORATION ETHNOGRAPHICAL MUSEUM, BERLIN] In 1908 Dr. Manuel Gamio conducted an important excavation of an ancient building at the site known as the monuments of Alta Vista, near Chalchihuites, Zacatecas, in northern Mexico. In a large chamber called the Hall of the Columns, Gamio found two mosaics in a small circular compartment in the concrete floor. One of these was a disc of yellow pottery encircled by a ring of wood, the entire object being about two and three-quarters inches in diameter and three-eighths of an inch thick. The wooden ring bore traces of a coating of resin, and many tiny bits which formed the mosaic incrustation were found with it, although not in place. The bits that had formed the mosaic were thin plates of worked turquois, beryl, and steatite. From the fact that the disc contained perforations, evidently for suspension, Gamio described it as a breast ornament. The other mosaic piece Gamio believes to have been a labret. He writes that “at first glance its shape may be described as resembling the bridge of a violin.... Its nucleus is wood, carved to represent two symmetrical figures of an alligator (_caiman_), united at the belly. Crowning the head are two head plumes, each having two branches. Above the point of union of the two reptiles there is a square projection with a perforation.”[78] The surface of the ornament had been covered with small spherical plates of turquois, beryl, and steatite. Near these two mosaic ornaments were found numerous small pieces of turquois and beryl of different shapes.