ITS ANCESTORS AND RELATIONS 



17 



coveries in North America announced by Professor 

 Marsh ; but we know as yet too little of these to be 

 able to form any satisfactory opinion as to their 

 affinities, or to pronounce with any certainty whether 

 they carry back the pedigree of the perissodactyle group 

 beyond the commencement of the Tertiary period. At 

 present the balance of evidence is rather in favour of 

 their relationship with the earlier and more primitive 

 forms just mentioned. We have, however, certain 

 knowledge that when the land which formed the 

 bottom of the great cretaceous ocean which flowed over 

 a considerable part of the present continents of Europe 

 and North America was lifted above the level of the 

 water and became fitted to be the abode of terrestrial 

 animals, it was very soon the habitation of vast numbers 

 of herbivorous and hoofed mammals. 



The remains of animals to which it is possible to 

 trace back the modern horse by a series of successive 

 modifications without any great break are found in 

 abundance in the lower strata of the great lacustrine 

 formations assigned to the Eocene period spread over 

 considerable portions of the present territories of New 

 Mexico, Wyoming, and Utah, in North America. 

 Similar animals also existed in other parts of the 

 world, but in Europe the hitherto-discovered fragments 

 which prove their existence are in a less complete and 

 satisfactory condition for investigation. Negative evi- 



c 



