56 THE GEOLOGICAL EVIDENCES 



mammals. The history of the horse furnishes, 

 perhaps, the most complete series of structural 

 modifications which permit us to trace the ances- 

 try of an animal in very nearly its minutest 

 details. The chart before you indicates these mod- 

 ifications in a series of horse-like animals which 

 carries the line of descent of our modern animal 

 back to the Eocene period, and to an animal 

 so very different, that were it known by itself 

 alone, it would be classified by zoologists, not only 

 as a species distinct from the modern horse, but 

 as a distinct genus, representing an entirely differ- 

 ent family, and even a wholly different sub-order. 

 The connecting ties, however, absolutely estab- 

 lish the serial line of progression, and indelibly 

 mark the pedigree. The history of the Euro- 

 pean horse is almost as complete as that of the 

 American, but remarkable though it may appear 

 on any but an evolutionary hypothesis, its first 

 ancestral forms include an animal different from 

 any of the earlier equine progenitors of the 

 New World, and one that holds equal claim to 



