Then again, it occurs to us, that this method, of attaching a time-value to percentages of extinct or living species, would make the sub-fossil remains of the bison on the Western prairies almost infinitely =older= than those of the lion, hippopotamus, etc., in the Pleistocene beds of Europe; for (except for some few specimens artificially preserved, and which may be ignored in this connection) the bison is to-day absolutely extinct, while the Pleistocene mammals are found by the thousand in the proper localities and show no signs of surrender in the struggle for existence. Similar comparisons might be made between the great wingless birds of Madagascar, Mauritius and New Zealand, and the many cases of "persistent" forms which have survived unchanged from Carboniferous, Silurian, or Cambrian times, a period of time which, in the language of the current geology, means quite a large fraction of eternity. But all of these considerations show that the mere fact of certain species being extinct and others being now alive, is no trustworthy guide in determining the relative age of their remains, until we first find out =how they happened to become extinct=. The inquiry as to the =how= and the =when= (relatively) is an absolutely essential preliminary in any such investigation; and is inseparably united in nature with the general question of how the great geological changes have taken place in the past. Of course, if everything like a world-catastrophe is =a priori= denied; if, in other words, it is settled from the first that all these fossils living and extinct did not live contemporaneously with each other, the living ones being simply the lucky survivors of stupendous changes in which the others perished, then all pretense of a scientific investigation of the subject is at an end. If a coroner has it settled beforehand that an accident or a murder could not possibly have occurred, then his profession of a candid _post mortem_ examination is only a farce; for he does not hold it to find out anything, since he knows everything essential about it beforehand. Uniformitarians would certainly make poor coroners, or for that matter poor investigators of law or history, or anything else. Will some one please give us a reasonable explanation of why the lion, hippopotamus, rhinoceros, and elephant shifted from England to the tropics? Or will they explain how, at this same general time, some elephants and rhinoceroses got caught in the merciless frosts of Northern Siberia so suddenly that their flesh has remained untainted all these centuries, and is now, wherever exposed, greedily devoured by the dogs and wolves?