now
living in the Mediterranean is still considerable; but it no longer
predominates, as in the South of Italy and part of Sicily, over the
unknown species. Although occurring in localities which are removed
several degrees farther from the equator (as at Sienna, Parma, Asti,
&c.), the shells yield clear indications of a warmer climate. This
evidence is of great weight, and is not neutralized by any facts of a
conflicting character; such, for instance, as the association, in the
same group, of individuals referable to species now confined to arctic
regions. Whenever any of the fossil shells are identified with living
species foreign to the Mediterranean, it is not in the Northern Ocean,
but nearer the tropics, that they must be sought: on the other hand, the
associated unknown species belong, for the most part, to _genera_ which
are now most largely developed in equinoctial regions, as, for example,
the genera Cancellaria, Cassidaria, Pleurotoma, Conus, and Cypraea.

On comparing the fossils of the tertiary deposits of Paris and London
with those of Bourdeaux, and these again with the more modern strata of
Sicily, we should at first expect that they would each indicate a higher
temperature in proportion as they are situated farther to the south.
But the contrary is true; of the shells belonging to these several
groups, whether freshwater or marine, some are of extinct, others of
living species. Those found in the older, or Eocene, deposits of Paris
and London, although six or seven degrees to the north of the Miocene
strata at Bourdeaux, afford evidence of a warmer climate; while those of
Bourdeaux imply that the sea in which they lived was of a higher
temperature than that of Sicily, where the shelly strata were formed six
or seven degrees nearer to the equator. In these cases the greater
antiquity of the several formations (the Parisian being the oldest and
the Sicilian the newest) has more than counterbalanced the influence
which latitude would otherwise exert, and this phenomenon clearly points
to a gradual and successive refrigeration of climate.

_Siberian Mammoths._--It will naturally be asked, whether some recent
geological discoveries bringing evidence to light of a colder, or as it
has been termed "glacial epoch," towards the close of the tertiary
periods throughout the northern hemisphere, does not conflict with the
theory above alluded to, of a warmer temperature having prevailed in the
eras of the Eocene,