I have hardly the space to repeat here my argument about the extremely fanciful way in which geologists classify the various members of the Tertiary group and the Pleistocene. And yet I must say a few words. I have tried to show the utter nonsense of the common custom of classifying these beds according to the percentage of living and extinct forms which they contain, when the real fact is that the number and kinds of the ancient life-forms which have survived into the modern era is a purely fortuitous circumstance, being limited solely to those lucky ones which could stand the radical change from a tepid water or a genial air to the ice and frosts which they now experience, to mention only one circumstance of that cosmic convulsion which we now know to have really intervened between that ancient world and our own. =YET IT IS ON SUCH EVIDENCE ONLY= that these Pleistocene forms are separated from the Tertiaries, or that the Tertiaries themselves are classified off--at least as far as the invertebrates and the plants are concerned. No one claims that the so-called Glacial beds can be sharply distinguished from other deposits on purely mechanical make-up. Indeed, I am strongly of the opinion that very many Archaean soils, totally unfossiliferous themselves, and resting on unfossiliferous rocks, have been assigned to the "Glacial age," merely because their discoverers did not know what else to do with them. When beds contain fossils, the latter are the one and only guide in determining age; but in view of the purely arbitrary character of this method of classifying off the Tertiary and post-Tertiary rocks, I do not see where we are going to =draw the line= when we once admit that the post-Tertiary beds contain only "derived fossils." It seems to me truly astonishing that shrewd reasoners, like Howorth and Dr. Woodward, have not seen the dangerous character of this precedent which they have admitted. For with that marvelous climate of all geological time continuing right up to that fatal day when it was "abruptly terminated," and the mammoth and his fellows were caught in the merciless frosts which now hold them, the percentage of all the lucky forms of life, plants, invertebrates, or mammals, which could stand such a change and "persist" into our modern world, must be =utterly nonsensical as a test of age= even from their standpoint. In resuming the main argument of this chapter, I need only summarize by saying that the evidence is conclusive that all geological time down to this sharp "dividing line" was characterized by a surprisingly mild and uniform climate over all the earth. The modern period is characterized by terrific extremes of heat and cold; and now little or nothing can exist where previously plant and animal life flourished in profusion.