e same
area, in accordance with the fluctuations of temperature which
have been shown by Mr James Geikie to have characterised the
Glacial period as a whole. We can thus readily account for the
intermixture which is sometimes found of northern and southern
types of Mammalia in the same deposits, or in deposits apparently
synchronous, and within a single district. Lastly, at the final close
of the arctic cold of the Glacial period, and the re-establishment
of temperate conditions over the northern hemisphere, a reversal
of the original process took place--the northern Mammals retiring
within their ancient limits, and the southern forms pressing
northwards and reoccupying their original domains.

The _Invertebrate_ animals of the Post-Pliocene deposits require
no further mention--all the known forms, except a few of the shells
in the lowest beds of the formation, being identical with species
now in existence upon the globe. The only point of importance in
this connection has been previously noticed--namely, that in
the true Glacial deposits themselves a considerable number of
the shells belong to northern or Arctic types.

As regards the _Vertebrate_ animals of the period, no extinct
forms of Fishes, Amphibians, or Reptiles are known to occur,
but we meet with both extinct Birds and extinct Mammals. The
remains of the former are of great interest, as indicating the
existence during Post-Pliocene times, at widely remote points
of the southern hemisphere, of various wingless, and for the
most part gigantic, Birds. All the great wingless Birds of the
order _Cursores_ which are known as existing at the present day
upon the globe, are restricted to regions which are either wholly
or in great part south of the equator. Thus the true Ostriches are
African; the Rheas are South American; the Emeus are Australian;
the Cassowaries are confined to Northern Australia, Papua, and the
Indian Archipelago; the species of _Apteryx_ are natives of New
Zealand; and the Dodo and Solitaire (wingless, though probably
not true _Cursores_), both of which have been exterminated within
historical times, were inhabitants of the islands of Mauritius
and Rodriguez, in the Indian Ocean. In view of these facts, it
is noteworthy that, so far as known, all the Cursorial Birds
of the Post-Pliocene period should have been confined to the
same hemisphere as that inhabited by the living representatives
of the order. It is still further interesting to noti