Page:Popular Science Monthly Volume 7.djvu/54

44 formed part of living bodies; that they may be the "ash" of protoplasm; that the "rupes saxei" are not only "temporis," but "vitæ filiæ;" and, consequently, that the time during which life has been active on the globe may be indefinitely greater than the period the commencement of which is marked by the oldest known rocks, whether fossiliferous or unfossiliferous.

And thus we are led to see where the solution of a great problem and apparent paradox of geology may lie. Satisfactory evidence now exists that some animals in the existing world have been derived by a process of gradual modification from preëxisting forms. It is undeniable, for example, that the evidence in favor of the derivation of the horse from the later tertiary Hipparion, and that of the Hipparion from Anchitherium, is as complete and cogent as such evidence can reasonably be expected to be; and, the further investigations into the history of the tertiary mammalia are pushed, the greater is the accumulation of evidence having the same tendency. So far from paleontology lending no support to the doctrine of evolution—as one sees constantly asserted—that doctrine, if it had no other support, would have been irresistibly forced upon us by the paleontological discoveries of the last twenty years.

If, however, the diverse forms of life which now exist have been produced by the modification of previously-existing less divergent forms, the recent and extinct species, taken as a whole, must fall into series which must converge as we go back in time. Hence, if the period represented by the rocks is greater than, or coextensive with, that during which life has existed, we ought, somewhere among the ancient formations, to arrive at the point to which all these series converge, or from which, in other words, they have diverged—the primitive undifferentiated protoplasmic living things, whence the two great series of plants and animals have taken their departure.

But, as a matter of fact, the amount of convergence of series, in relation to the time occupied by the deposition of geological formations, is extraordinarily small. Of all animals the higher Vertebrata are the most complex; and among these the carnivores and hoofed animals (Ungulata) are highly differentiated. Nevertheless, although the different lines of modification of the Carnivora and those of the Ungulata, respectively, approach one another, and, although each group is represented by less differentiated forms in the older tertiary rocks than at the present day, the oldest tertiary rocks do not bring us near the primitive form of either. If, in the same way, the convergence of the varied forms of reptiles is measured against the time during which their remains are preserved—which is represented by the whole of the tertiary and mesozoic formations—the amount of that convergence is far smaller than that of the lines of mammals, between the present time and the beginning of the tertiary epoch. And it is a broad fact that, the lower we go in the scale of organization,