In this survey of aboriginal America we have been impressed by the contrast between two diverse aspects of the control of human activities by physical environment. We saw, in the first place, that in our own day the distribution of culture in America is more closely related to climatic energy than to any other factor, because man is now so advanced in the arts and crafts that agricultural difficulties do not impede him, except in the far north and in tropical forests. Secondly, we have found that, although all the geographical factors acted upon the Indian as they do today, the absence of metals and beasts of burden compelled man to be nomadic, and hence to remain in a low stage of civilization in many places where he now can thrive. In the days long before Columbus the distribution of civilization in the Red Man's Continent offered still a third aspect, strikingly different both from that of today and from that of the age of discovery. In that earlier period the great centers of civilization were south of their present situation. In the southern part of North America from Arizona to Florida there are abundant evidences that the Indians whom the white man found were less advanced than their predecessors. The abundant ruins of Arizona and New Mexico, their widespread distribution, and the highly artistic character of the pottery and other products of handicraft found in them seem to indicate that the ancient population was both denser and more highly cultured than that which the Europeans finally ousted. In the Gulf States there is perhaps not much evidence that there was a denser population at an earlier period, but the excellence of the pre-Columbian handicrafts and the existence of a decadent sun worship illustrate the way in which the civilization of the past was higher than that of later days. The Aztecs, who figure so largely in the history of the exploration and conquest of Mexico, were merely a warlike tribe which had been fortunate in the inheritance of a relatively high civilization from the past. So, too, the civilization found by the Spaniards at places such as Mitla, in the extreme south of Mexico, could not compare with that of which evidence is found in the ruins. Most remarkable of all is the condition of Yucatan and Guatemala. In northern Yucatan the Spaniards found a race of mild, decadent Mayas living among the relics of former grandeur. Although they used the old temples as shrines, they knew little of those who had built these temples and showed still less capacity to imitate the ancient architects. Farther south in the forested region of southern Yucatan and northern Guatemala the conditions are still more surprising, for today these regions are almost uninhabitable and are occupied by only a few sickly, degraded natives who live largely by the chase. Yet in the past this region was the scene of by far the highest culture that ever developed in America. There