More or less speculation regarding the origin of pueblo culture is the usual and perhaps proper accompaniment of nearly all treatises bearing on that subject. Early writers on the Aztec culture, aided by a vague tradition of that tribe that they came from the north, pushed the point of emigration farther and farther and still farther north, until finally the pueblo country was reached. Pueblo ruins are even now known locally as "Aztec ruins." Logically the inhabited villages should be classed as "Aztec colonies," and such classification was not unusual when the country came into the possession of the United States some fifty years ago. As our knowledge of the pueblo culture increased, a gradual separation between the old and the new took place, and we have as an intermediate hypothesis many "Aztec ruins," but no "Aztec colonies." Finally, as a result of still further knowledge, the ruins and the inhabited pueblos are again brought together; several lines of investigation have combined to show the continuity of the old and the present culture, and the connection may be considered well established. But there is still a disposition to regard the cliff ruins as a thing apart. The old idea of a separate race of cliff dwellers now finds little credence, but the cliff ruins are almost universally explained as the results of extraordinary, primitive, or unusual causes. The intimate relation between the savage and his physical environment has already been alluded to. Nature, or that part of nature which we term physical environment, enters into and becomes part of the life of the savage in a way and to an extent that we can hardly conceive. A change of physical environment does not produce an immediate change in the man or in his arts, but in time such must inevitably result. Twenty-five years ago the savage of the plains and the savage of the pueblo country were regarded as distinct races, "as different from each other as light is from darkness;" yet the differences which appeared so striking at first have become fewer and fewer as our knowledge of the Indian tribes increased, and those which remain today can almost all be attributed to a difference in physical environment.