THE STORY OF THE HORSE 221 
gree, actually illustrated by real examples, following 
each other in time through the geological history. A 
few of these lines are gradually becoming plain, and 
none of them is clearer than the pedigree of our fa- 
miliar and much loved horse. The example is a par- 
ticularly interesting one, not only because of our af- 
fection for the animal, but because the horse origi- 
nated in all likelihood in North America on the land 
occupied to-day by our Western plains. As though 
he loved the country of his ancestors, he returned 
after having circled the globe, and once more went 
wild in the home of his forefathers. The problem 
was first worked out in Europe and later elaborated 
in this country. Now the history gets its finest ex- 
pression in the American Museum of Natural His- 
tory in New York City. The collection of fossil 
horses in that institution surpasses in completeness 
and in excellence of mounting and of sympathetic 
restoration any similar collection representing the an- 
cestry of any other animal in the world. 
In the table of Geological Times, given in chapter 
six, the era of recent life known as the Cenozoic is 
seen to occupy something like five million years. This 
figure, as was previously suggested, is very uncer- 
tain, and may be three or may be six, but is safely 
represented in millions. Through most of this time 
stretches what is known as the Age of Mammals, the 
