Pueblos both ancient and modern can be placed in one or another of the above-mentioned types, although in some cases two of these types may be combined, making a composite building reaching a considerable size. In whatever type the pueblo is placed, the circular-form room also exists, either enclosed in the rows or free from the rows of secular rectangular chambers. The pyramidal, rectangular, and linear types are comparatively modern, having persisted to the present day, when many are inhabited; the circular type is confined wholly to ancient times and is no longer inhabited. Open pueblos are independent of cliffs as distinguished from those dependent or those built within caves. Dependent and independent buildings are morphologically the same, but the dependent or so-called cliff pueblos were not inhabited at the advent of the Europeans. An examination of the main features of the groups above mentioned reveals certain common features, an enumeration of which still further defines the pueblo type. All have both the terraced and the community form. They are all accompanied by a sacred room of circular form compactly enclosed in the mass of building or built separate from it. If we examine the distribution geographically of the pueblo type, ancient and modern, we find it limited to the area including the southern parts of Colorado, Utah, and the greater part of New Mexico, its highest development occurring in the mountains. It is preeminently limited to a plateau region, and theoretically we may suppose that it owes its peculiarities to the characteristic physiographic conditions of this environment. If we consider this type chronologically we find the oldest and best examples situated in the northern part of the area; the evidence is good that influence from that nucleus extended west and south, the architecture as we recede from the place of origin becoming inferior or losing some of its essential features, probably on account of contact with unrelated peoples. This modification and the accompanying departure from the type are especially marked in extensions that came in contact with people who constructed rooms compactly united, from southern Arizona, where environmental conditions show a great contrast to the mountain region in which the pueblo originated. The plains bordering the Gila and its tributaries are low and level, covered with a vegetation wholly different from that of the mountain canyons in which pueblo buildings originated. Climatically southern Arizona is very warm throughout the year; the mountains of Colorado are covered with snow from November to March, inclusive. These conditions have led in the former region to the separation of the dwellings or a more open life of the aborigines; the rooms are larger and not crowded together as in pueblos; the material used in their construction is also different; stone is not available; its absence led to the use of clay and mud as the only materials out of which man could construct