This colonizing extension of the old Mexican race must have taken place at a remote period in the past; for what has been said of the antiquity of the Mound-Builders shows that a very long period, far more than two thousand years, it may be, must have elapsed since they left the Valley of the Ohio. Perhaps they found the country mostly unoccupied, and saw there but little of any other people until an irruption of warlike barbarians came upon them from the Northwest. In speculating on the causes of their withdrawal after centuries of occupation, absolute certainty is impossible, and we have no means of going much beyond mere conjecture. We may suppose as most probable that an influx of barbarians destroyed their border settlements, interrupted their mining operations, and caused them to retire gradually toward the Gulf. Fragments of their communities may have become incorporated with the barbarous tribes. This conjecture has been used to explain certain exceptional peculiarities noticed in some of the wild Indian tribes. For instance, it has been suggested that the Mandan Indians were a separated and lost fragment of the mound-building people, they being noticeably unlike other Indians in many respects, lighter in color, and peculiar in manners and customs. What is conjectured may be true, but we have no means of proving its truth. That the Mandans were like what a lost community of Mound-Builders might have become by degeneration through mixture and association with barbarians may be supposed, but the actual history of that remarkable tribe might give its peculiarities a very different explanation. The Mandans were supposed to be a branch of the Dacotahs. They may have been, like the Navajos, a changed community of Pueblos, but any attempt to explain them by means of conjecture is useless. The supposition that the Toltecs and the Mound-Builders were the same people seems to me not improbable. The reasons for it will be stated when we come to a discussion of the antiquities, books, and traditions of Central America. I will only say here that, according to dates given in the Central American books, the Toltecs came from “Huehue-Tlapalan,” a distant country in the northeast, long previous to the Christian era. They played a great part and had a long career in Mexico previous to the rise of their successors in power, the Aztecs, who were overthrown by the Spaniards. IV. MEXICO AND CENTRAL AMERICA.