Long before the dawn of the Columbian era, therefore, the Amerind peoples had become, through the influences indicated, a world-race by themselves, existing in various stages of the same general culture, and with a rising and a declining of tribes and stocks directed by environment and circumstances. The great stocks surviving at the beginning of the Columbian era may be approximately traced by their languages, in layers, from Panama northward, about as they expanded mainly eastward of the Sierra Nevada in response to the gradual relief from the pressure of the cold. The Yucatec tribes had held the region south of the Tehuantepec isthmus, and owing to this slight barrier, and perhaps to another barrier of a strait through the land about on the line of the proposed Nicaragua canal, had developed somewhat differently from tribes to the north, and may also have preserved more of their original character. Thence stretching north far into the United States was the great composite Shoshone, or Uto-Aztecan family, in all its variations, with what appears to be an “island” of Athapascans or Boreal men preserved in its midst by glacial conditions lingering in the high regions near the Mexico-United States line; then follows the Siouan; then the widespread Algonquian stock; next the Athapascan; and finally the Eskimauan, which had always been held against the edge of the glaciers by the back pressure of the southern stocks, and being most remote was less affected by filtration from the development centre, and thus remains to-day a more differentiated stock than any other.[3] The western arm of these stocks was generally farther north than the eastern because the climate was and is milder in the west, the trend of the ice front being now, and apparently always having been, N.W. to S.E. Distribution of skill in pottery follows about the same lines, “petering” out with stocks farthest from the Yucatec centre. The Algonquins crowded the Athapascans off to the N.W., and together they crowded the Eskimo to the limits of human subsistence. In California many stocks found refuge in a climate kept comparatively mild by the ocean currents, where they secured subsistence on fish, and went no farther south. Along the Gulf coast were other tribes resting somewhat aside from the great continental ebb and flow, while in Florida and in the islands of the Caribbean region there was sufficient separation to produce a slight differentiation from the surging continental stocks. Remnants of other stocks were scattered here and there through the regions below the glaciated area. Mingled with all these developments there were probably certain traits and “tinges” derived from earlier ancestry, and these, with the similarity of development of all races under like conditions prevailing wherever human beings can live, fully account for resemblances to other-world tribes and peoples that have caused so much speculation.