s of the animal
kingdom. The impulse is natural, and, if the resulting tables are not
accepted with too much confidence, the result is not undesirable. The
truth of the matter is that all of these pedigrees are more or less
hypothetical. They simply show what connection seems most likely. In
all of them are spaces filled with doubtful names. Each addition to
our acquaintance with the past history of animals necessitates
revision of our tables. The student of fossils, trying to rebuild in
imagination the world of the past, finds himself often strangely
unable to link these animals together. The result is that the more we
know of fossils, the more distrustful we become of the easy
connections we have been making between groups. Accordingly we are
more than commonly pleased when we find the clear indication of a
genuine pedigree, 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 familiar and much loved horse. The example is a
particularly interesting one, not only because of our affection for
the animal, but because the horse originated 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 expression
in the American Museum of Natural History 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 ancestry 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
uncertain, 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 Tertiary Age. Its close, occupying only the last
few hundred thousand years, is known as the Age of Man, the
Quaternary. Through perhaps three or four millions of these years
stretches the known pedigree of the horse.

When we go back to the early Ter