In the field of minor arts and ornaments, the people of this period reached a high degree of achievement. _Olivella_ shell beads were still widely used as well as stone beads and stone and shell pendants carved in the forms of birds and animals. Turquoise, which first seems to have been used in late Basketmaker times, was used extensively for some of the finest ornaments, not only for beads and pendants but also in beautiful mosaics. [Illustration: Chaco-style pottery bowl. Maximum diameter, 9″; Height, 4¼″.] However, it is the large multistoried pueblos of the Chaco Canyon and the great cliff dwellings of the Mesa Verde that attract the most attention. The native sandstone at Chaco Canyon made an excellent building material—it was easily obtainable, it fractured along natural cleavage planes into thin slabs, and it could be ground and pecked into large rectangular blocks. Both the availability of sandstone and the relative ease with which it could be worked were important factors in developing the Chaco style of architecture. Some of these pueblos may have been as high as five stories; most were at least three or four stories. All show signs of constant alteration in individual rooms and in their general layout, as though some feverish urge was forcing the people to keep shifting the arrangement of their dwellings. Not all the rooms in any of the large pueblos were occupied simultaneously; usually the rooms toward the rear were used for storage or, in many cases, as dumps for refuse and garbage. Occasionally, burials are found in them. All the great Chaco pueblos form self-contained units—that is, they were built around central plazas or courtyards, as in the case of Pueblo Bonito, with a low row of single-storied rooms closing off the formerly open side of the plaza, or they were roughly rectangular with closely knit contiguous rooms and internal kivas as in Yellow House. This closure, plus the fact that the doors and windows which formerly had opened outward at the rear or sides are now sealed up, has led many people to believe the later parts of this period were marked by trouble and strife and that this self-containment was a defensive measure.