126 THE CANADIAN NATURALIST. [June 



Supposing that Palgeotheriunij Hipparion and Equus arc links 

 in a chain extending from the Eocene Tertiary to the present 

 time, can we suppose that by tracing the same series further 

 back it might include any Mammjil. We must answer 

 decidedly not, for if the whole time from the Eocene to the 

 present has been required to produce the comparatively small 

 change required from Palaeotherium to horse, that in other 

 cases would carry us back to the iMesozoic period, long before we 

 have any evidence of the existence of " placental mammals." In 

 other words, the Tertiary and Modern Periods will give us 

 time enough only to effect changes of Mammals within the 

 order Pachydermata, and perhaps in only one section of that 

 order. The other orders must therefore constitute separate 

 series, and these series must have been advancing abreast of each 

 other. Had each series a separate origin, or is there any 

 Mammalian stock in the Mesozoic from which, at the beginning 

 of the Tertiary, these several lines of types hiay have diverged ? 

 Here our information fails. We know only a few small Mar- 

 supial Mammals in the Mesozoic. On our hypothesis it is 

 possible that these may have been the progenitors of the more 

 varied and advanced Marsupials of the Tertiary and Modern 

 periods, but scarcely of the placental Mammals of the Eocene. 

 There may have been placental Mammals, unknown to us, in the 

 Mesozoic, which may constitute the required stock. The reptiles 

 of the Mesozoic utterly fail to give us the necessary links. If 

 they were changing into anything it was into birds, not into 

 Mammals. 



Again, the time in which the horse and its supposed progenitors 

 have lived is one of continuous, unbroken succession of species. 

 More especially in the later Tertiary there seems the best 

 evidence of gradual extinction and introduction of species, without 

 any very wide-spread and wholesale destruction, and this not- 

 withstanding the intervention of that period of cold and of 

 submergence of land in the Northern hemisphere, which has given 

 rise to all the much-agit itcd glacial theories of our time. Can we 

 affirm that such piecemeal work has continued throughout 

 Geological time? At this point opens the battle between the 

 'Jatastrophists and Uniformitarians in lleology, a battle which I 

 am not about to fight over again here. I have ekewhcre stated 

 reasons for the belief that neither view can be maintained 

 without the other, and that Geological time has consisted of 



