[Footnote 10: As this term has been already defined, it is here used without further explanation. For a full discussion of these structures, see “A Study of Pueblo Architecture,” by Victor Mindeleff, in 8th. Ann. Rep. Bur. Eth., 1886-87, Washington, 1891.] The circular kiva is a survival of an ancient type--a survival supported by all the power of religious feeling and the conservatism in religious matters characteristic of savage and barbarous life; and while most of the modern pueblos have at the present time rectangular kivas, such, for example, as those at Tusayan, at Zuñi, and at Acoma, there is no doubt that the circular form is the more primitive and was formerly used by some tribes which now have only the rectangular form. Still the abandonment of the circular and the adoption of the rectangular form, due to expediency and the breaking down of old traditions, was a very gradual process and proceeded at a different rate in different parts of the country. At the time of the Spanish conquest the prevailing form in the old province of Cibola was rectangular, although the circular kiva was not entirely absent; while, on the other hand, in the cliff ruins of Canyon de Chelly, whose date is partly subsequent to the sixteenth century, the circular kiva is the prevailing, if not the exclusive form. But notwithstanding this the Hopi Indians of Tusayan, to whom many of the Canyon de Chelly ruins are to be attributed, today have not a single circular kiva. The reason for this radical departure from the old type is a simple one, and to be found in the single term environment. The savage is truly a child of nature and almost completely under its sway. A slight difference in the geologic formations of two regions will produce a difference in the arts of the inhabitants of those regions, provided the occupancy be a long one. In the case of the Tusayan kivas the rectangular form was imposed on the builders by the character of the sites they occupied. The requirement that the kiva should be under ground, or partly under ground, was a more stringent one than that it should be circular, and with the rude appliances at their command the Tusayan builders could accomplish practically nothing unless they utilized natural cracks and fissures in the rocks. Hence the abandonment of the circular form and also of the more essential requirement, that the kiva should be inclosed within the walls of the village or within a court; the Tusayan kivas are located indiscriminately in the courts and on the outskirts of the village, wherever a suitable site was found, some of them being placed at a considerable distance from the nearest house.