ent courses; and the fact that the
same species are to be met with in the caves of France, Switzerland and
Britain implies that our island formed part of the continent, and that
there were no physical barriers to prevent their migration from the Alps
as far to the north-west as Ireland.

The same conclusion may be gathered from the exploration of caves in the
south of Europe, which has resulted in the discovery of African species,
in Gibraltar, Sicily and Malta. In the first of these the spotted hyena,
the serval and Kaffre cat lie side by side with the horse, grizzly bear
and slender rhinoceros (_R. leptorhinus_)--see Falconer's
_Palaeontographical Memoirs_. To these African animals inhabiting the
Iberian peninsula in the Pleistocene age, Lartet has added the African
elephant and striped hyena, found in a stratum of gravel near Madrid,
along with flint implements. The hippopotamus, spotted hyena and African
elephant occur in the caves of Sicily, and imply that in ancient times
there was a continuity of land between that spot and Africa, just as the
presence of the _Elephas antiquus_ proves the non-existence of the
Straits of Messina during a portion, to say the least, of the
Pleistocene age. A small species of hippopotamus (_H. Pentlandi_) occurs
in incredible abundance in the Sicilian caves. It has also been found in
those of Malta along with an extinct pigmy elephant species (_E.
Melitensis_). It has also been discovered in Candia and in the
Peloponnese. For these animals to have found their way to these regions,
a continuity of land is necessary. The view advanced by Dr Falconer and
Admiral Spratt, that Europe was formerly connected with Africa by a
bridge of land extending southwards from Sicily, is fully borne out by
these considerations. The present physical geography of the
Mediterranean has been produced by a depression of land to the amount of
about 400 fathoms, by which the Sicilo-African and Ibero-African
barriers have been submerged, and Crete and Malta separated from the
South-European continent. It is extremely probable that this submergence
took place at the same time that the adjoining sea-bottom was elevated
to about the same amount so as to constitute that region now known as
the Sahara.

_Pleistocene Caves of the Americas and Australia._--The Pleistocene
caverns of the Euro-Asiatic continent contain the progenitors of the
animals now alive in some parts of the Old World, the extinct forms
being clo