The application of the hypothesis to the map brings out some interesting results. In the first place, it may be seen that in the lowest mounds, such as those in the northwestern corner of the sheet, on the southern margin, and southwest of the well-marked mound on the eastern margin, the contours are more flowing and the slopes more gentle than in others. This suggests that these smoothed mounds are older than the others, and, further, that their present height is not so great as their former height; and again, under this hypothesis, it suggests that the remains do not belong to one period, but that the interval which elapsed between the abandonment of the structures whose sites are marked by the low mounds and the most recent abandonment was long. In other words, this group, under the hypothesis, affords another illustration of a fact constantly impressed on the student of southwestern village remains, that each village site marks but an epoch in the history of the tribe occupying it--a period during which there was constant, incessant change, new bands or minor divisions of the tribe appearing on the scene, other divisions leaving the parent village for other sites, and the ebb and flow continuing until at some period in its history the population of a village sometimes became so reduced that the remainder, as a matter of precaution, or for some trifling reason, abandoned it en masse. This phase of pueblo life, more prominent in the olden days than at present, but still extant, has not received the prominence it deserves in the study of southwestern remains. Its effects can be seen in almost every ruin; not all the villages of a group, nor even all the parts of a village, were inhabited at the same time, and estimates of population based on the number of ruins within a given region, and even those based on the size of a given ruin, must be materially revised. As this subject has been elsewhere[1] discussed, it can be dismissed here with the statement that the Casa Grande group seems to have formed no exception to the general rule, but that its population changed from time to time, and that the extent of the remains is no criterion of the former population. [Footnote 1: See pp. 179-261 of this Report, "Aboriginal Remains in Verde Valley."]