re country without native flora; as to the other
species, we must imagine that the _migration during the gradual change
of climate has proceeded slowly and step by step across connected tracts
of country_. In that manner we may assume that our country has in the
course of time obtained its present covering of plants. Each of the
above-named elements in our flora has doubtless its corresponding
element in our fauna. The fauna and flora of a region stand in relation
of complicated dependence to each other. The animals live on the plants.
The fecundation of the plants takes place in a great degree by means of
insects; their seeds are often scattered by resident birds and
quadrupeds. Everything indicates that _conveyance to small distances is
the rule_, and that sudden and long migration is the exception."

The conviction which has been gained by zoologists and botanists, that
the British Islands once formed part of the Continent, is based on the
present British fauna and flora. The remains, however, of animals which
used formerly to live in these countries, such as the Mammoth, the Irish
Elk, the Cave Bear, and many others, tell us the same tale. They could
not have peopled England by swimming across the Channel, or even by
walking across solid ice, as has once been suggested. Nothing but a
land-connection induced them to explore this country more closely, and
finally to decide on settling there.

The origin of the British fauna will be discussed more in detail in the
third chapter. The methods of investigation adopted, along with a
general scheme of this book, will be found in the next.

The manner in which the origin of the fauna of any particular
continental area can be traced is very similar to that adopted in the
case of an island. Portions of the continent of Europe can be shown to
have been islands in former times. Thus the Crimea, now a peninsula
united to the mainland by the narrow isthmus of Perekop, must have been
an island in comparatively recent times. The absence of a number of
striking and familiar South Russian species of mammals and reptiles
proves this to have been the case. It was probably long after the
appearance of man, though before historic times, that these changes
took place.

We shall learn in the subsequent chapters, that by a careful study of
the fauna and flora the fact can be established, not only of the former
connection of an island with a continent, but also whether such union
existed