Protagonists of early man have argued that Folsom must date far, far back, or there would not be time for the evolution of the modern bison of the High Plains. Lately, however, Eiseley has developed a theory which does away with the long period of evolution from _Bison antiquus_ into _Bison bison_, and yet pins down Folsom to the end of the glaciers. There is some evidence that the kind of bison Folsom man hunted migrated up into Canada when the glaciers melted, and that the “modern” variety, which we call “buffalo,” came up from the south and took over the High Plains. As the temperature moderated over the whole northern hemisphere the plains of Canada began to resemble the plains of the United States, where the prey of Folsom man had flourished. The climate and the vegetation of the High Plains, moving north behind the ice, took _Bison antiquus_ along. The same northward movement of climate and vegetation occurred from Mexico to the High Plains, and it carried to their historic habitat the buffalo that have left their bones in old soils south of the border. The only place where we meet the two varieties of bison together is a peat bog in Minnesota.[18] The evidence that _Bison antiquus_ moved to Canada is not complete, but it is suggestive. There are accounts of bison horns from Athabasca “nearly twice the length of the Plains’ ones and much straighter.”[19] Ernest Thompson Seton provides the same kind of evidence.[20] The Canadian bison and the Folsom variety seem “suspiciously similar,” says Eiseley. Unfortunately, in 1925, before the bison of Athabasca—the second surviving race, _Bison bison athabascæ_—had been properly measured and observed, _Bison bison_ from the High Plains were brought north to breed with the Canadian variety. Eiseley feels it is a possibility that the Athabascan animals “represented, at least in a mixed form, the last of the Ice Age bison which early man had hunted in the western plains.”[21] If this is true, it means that Folsom man was fully developed in the period before the melting of the glaciers drove his favorite game north to Canada. It means, further, that he or his immediate forebears may have entered the plains 50,000 years ago when a corridor opened through the western ice fields. (See illustration, page 26.) The Folsom bison may also have gone northeast to the edge of New England. Grasslands extend from the High Plains of the classic Folsom point northeast to Illinois and Indiana, and ancient steppes once ran through Ohio to New York State and probably to New Jersey and southern New England.[22] Antevs suggests that late bands of Folsom men pursued their bison across this area. Certainly they left their cruder form of point in this part of the Middle West and the East.[23] But where, in this area, are the fossils of the extinct bison? The Mystery of Extinction