The data here published should not be interpreted to mean that the author regards the builders of the towers and great houses here described as evidences of a race other than the Indians. Indeed he believes that in both blood and culture they have left survivals among the modern Pueblos. He also does not hold that as a whole they necessarily belonged to a radically different phase of culture, notwithstanding the buildings they constructed show a greater variety of form and masonry superior to that of their descendants. The evidences are cumulative that there existed and disappeared in a wide geographical area of the Southwest a people whose buildings differed so much from those of any other area in North America that the area in which they occur may be designated as a characteristic one. The variety and type of buildings have a bearing on social organization. A large building composed of many units is probably but not necessarily later in time than a single house; an isolated single house would probably be of earlier construction than a collection of several single houses of the same character compactly arranged in a village; a complete consolidation of several houses of such a village into a community house would naturally be more modern than a group of isolated single houses. City blocks postdate hamlets. Between a stage indicated by single houses and one characterized by consolidated building, there is a phase in which the buildings are grouped in clusters and are not united. We may theoretically suppose that the single house was inhabited by one social unit as a clan or family. As the food quest became more intensified and defense more urgent, social units, as indicated by single houses, would be brought together, and as the population increased the amalgamation would be more complete. This social organization, in the beginning loose, in the course of time would become more homogeneous, and as it did so the union of these separate social units would have been closer; and if we combine with that tendency the powerful stimulus of protection, we can readily see how a compact form of architecture characteristic of the buildings here described was brought about. The element of defense in the villages with scattered houses does not appear to have been very important, but might be adduced to explain the consolidation of these into large community houses.