as to that period of cold which occurs at
the close of the Tertiary and beginning of the Modern period, it can
not be held to have constituted any such break as to be considered, as
it was at one time, an equivalent for the Biblical chaos. This is
proved by the survival through this period of a very large proportion
of the animals and plants still existing in the northern hemisphere.
The chronological system of animals and plants has been continuous, as
the Bible represents it, since their first appearance on earth.

It is further remarkable that while there is geological evidence of
climates colder than the present in the temperate regions, there is
equally good proof of warmer climates even within the arctic circle
than those of the cold temperate regions at present. It is difficult
to account for these vicissitudes of climate, and much controversy
exists on the subject; but it seems certain that in the earlier
Tertiary and Cretaceous periods, for example, the supplies of heat and
light were so diffused over the earth as to permit the growth of a
temperate vegetation in Greenland, and even in Spitzbergen.
Geologists, however unwillingly, have been obliged to admit this as
one of those great possibilities, altogether unexpected beforehand,
which have been developed in the history of our planet. Various modes
of explaining this succession of cold and warm periods have been
adopted, all more or less hypothetical. Lyell has argued that it may
be explained by a different distribution of land and water and of the
ocean currents. Croll accounts for it by the varying eccentricity of
the earth's orbit, in connection with the precession of the equinoxes.
Evans by a shifting of the axis of rotation of the earth. Drayson,
Bell, Warring, and others, by a change in the inclination of the
earth's axis. Others by the secular diminution of the internal heat of
the earth, and of that of the sun. Others by the supposed recurrence
of periods in which the sun gives more or less heat, or in which the
earth is passing through colder or warmer regions of space. As the
subject is of interest with reference to possible correspondences of
these great summers and winters of the earth with the stages of the
creative work, it may be well to notice shortly the relative merits of
these theories.

(1.) The hypothesis of Croll is one of the most ingenious and
elaborate of the whole; but it has two great defects. One is that the
causes alleged are so