44 THE POPULAR SCIENCE MONTHLY, 



formed part of living bodies ; tljat they may be the " ash " of proto- 

 plasm ; that the " rujies saxel " are not only " temporis,^'' but " vitoe 

 JilicB y " and, consequently, that the time during wliich life has been 

 active on the globe may be indefinitely greater than the period tlie 

 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 ))reexisting forms. It is unde- 

 niable, for example, that the evidence in favor of the derivation of the 

 horse from the later tertiary Hipparion^ and that of the Hipparion 

 from Anchitherhcm, 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 accu- 

 mulation of evidence having the same tendency. So far from paleon- 

 tology 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 jialeontological discov- 

 eries 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 Ave go back in time. Hence, if the 

 period represented by the rocks is greater than, or coextensive Avith, 

 that during which life has existed, we ought, somewhere among the 

 ancient formations, to arrive at the point to which all these series con- 

 verge, or from Avhich, in other words, they have diverged the primi- 

 tive 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 re- 

 lation to tlie time occupied by the deposition of geological formations, 

 is extraordiuai-ily small. Of all animals the higher Vertehrata are the 

 most complex ; and among these the carnivores and hoofed animals 

 ( Ungxdata) are highly differentiated. Nevertheless, although the dif- 

 ferent lines of modification of the Carnivora and those of the Ungu- 

 lata, respectively, approach one another, and, although each group is 

 represented by less difterentiated forms in the older tertiary rocks 

 than at the present day, tlie oldest tertiary rocks do not bring us 

 near the primitive form of either. If, in the same Avay, the conver- 

 gence of the varied forms of rejitiles 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, be- 

 tween the i^resent time and the beginning of the tertiary epoch. And 

 it is a broad fact that, the lower we go in the scale of organization, 



