As in all the other ruins of Verde valley, circular kivas are absent in the Red-rock country, and this fact, which has attracted the attention of several observers, is, I believe, very significant. Although as yet our knowledge of the cliff houses of the upper Gila and Salado and their numerous tributaries is very fragmentary, and generalization on that account unsafe, it may be stated provisionally that no circular kivas have yet been found in any ruins of the Gila-Salado watershed. This form of kiva, however, is an essential feature of the cliff dwellings of Rio Colorado, especially of those along its affluents in southern Colorado and northern New Mexico. Roughly speaking, then, the circular kiva is characteristic of the ruins of this region and of certain others in the valley of the Rio Grande, where they still survive in inhabited pueblos. Circular ruins likewise are limited in their distribution in the Southwest, and it is an interesting fact that the geographic distribution of ancient pueblos of this form is in a general way the same as that of circular kivas. There are, of course, many exceptions, but so far as I know these can readily be explained. No ruins of circular dwellings occur in the Gila-Salado drainage area, where likewise no circular kivas have been observed. Moreover, the circular form of dwelling and kiva is distinctively characteristic of prehistoric peoples east of Tusayan, and the few instances of their occurrence on its eastern border can readily be explained as extra-Hopi. The explanation of these circular kivas advanced by Nordenskiöld and the Mindeleffs, that they are survivals of round habitations of nomads, has much to commend it; but whether sufficient or not, the geographic limitation of these structures tells in favor of the absence of any considerable migration of the prehistoric peoples of the upper Colorado and Rio Grande watersheds southward into the drainage area of the Gila-Salado. Had the migration been in that direction it may readily be believed that the round kiva and the circular form of dwelling would have been brought with it. The round kiva has been regarded as a survival of the form of the original homes of the nomad, when he became a sedentary agriculturist by conquest and marriage.