In addition to these, there was also a large number of animals
whose home is in the temperate regions of the earth--animals
that thrive in neither extremes of heat and cold. This includes
a great many animals of the deer kind, several varieties of
bears and horses; in fact, the majority of those with which we
are acquainted.<13>

Now, what conclusion follows from this assemblage of animals?
Many theories have been put forward in explanation. It has been
suggested that Europe at that time had a climate not unlike that
of some portions of the earth at present; that is, a long and
severe Winter was followed by a short but warm Summer.
During the Winter reindeer and other northern animals would
press from the north in search of food, but would retire on the
approach of Spring, when their feeding grounds would in turn be
occupied by bisons and animals of a southern habitat.
In confirmation of this view it is pointed out that a vast
collection of bones, from the bottom of a sink-hole or pond in
Derbyshire, England, conclusively show that in the summer-time
it was visited by bisons with their calves, and in Winter by
reindeer.<14> This theory is open to a great many objections.
As is well known, some animals make quite extensive migrations
annually, but we can scarcely believe that heavy, unwieldy
animals like the hippopotamus, were then such industrious
travelers as to wander every year from Italy to Northern England
and return.<15> But the very ground on which this theory rests,
that of strongly contrasted summers and winters, could not be
true of Europe or the western portions of it, owing to the
presence of the Atlantic Ocean, and the influence which it